Symposium Organizers
Eckhard Quandt University Kiel
Manfred Wuttig University of Maryland
Tomoyuki Kakeshita Osaka University
Sebastian Faehler IFW Dresden
G1: Fundamentals of Magnetic Shape Memory Alloys
Session Chairs
Monday PM, November 30, 2009
Hampton (Sheraton)
9:45 AM - **G1.1
Nature of Short and Long Range Magnetic Order in Ni-Mn-based Martensitic Heusler Alloys and their Relationships to Magnetic Shape Memory and Magnetocaloric Effects.
Mehmet Acet 1 , Seda Aksoy 1 , Eberhard Wassermann 1 , Pascale Deen 2 , Lluis Manosa 3 , Antoni Planes 3
1 Experimental physics, Duisburg-Essen University, Duisburg Germany, 2 , Institut Laue-Langevin, Grenoble France, 3 Departament d’Estructura i Constituents de la Matèria, Universitat de Barcelona, Barcelona Spain
Show AbstractTo understand the cause of magnetic field induced effects in shape memory alloys, it is necessary to understand the nature of the magnetic coupling, particularly in the temperature-vicinity of the martensitic transition. We present results on field-induced strain, neutron diffraction, and neutron polarization analysis experiments on Ni-Mn-based martensitic Heusler systems and show that at temperatures just below the martensitic transformation, the magnetic short-range correlations are antiferromagnetic, whereas they persist as mixed ferromagnetic and antiferromagnetic at temperatures above the martensitic transition; and well beyond the Curie temperature of the austenite state. The results of further ferromagnetic resonance studies show that antiferromagnetic exchange in the martensite state persists down to the lowest temperatures and coexists with the long-range ferromagnetism below the austenite Curie temperature. We discuss the relationship of the nature of magnetic coupling to magnetic superelasticity and magnetocaloric effects.
10:15 AM - G1.2
Thermal and Magnetic Field-Induced Phenomena in Ni-Mn-Sn Heusler Alloy.
Volodymyr Chernenko 1 , Jesus Rodriguez Fernandez 2 , Jose Barandiaran 1 , Patricia Lazpita 1 , Jon Gutierrez 1 , D. Rojas 2
1 Electricidad y Electronica, University of Basque Country, Leioa Spain, 2 Fac. Ciencias, CITIMAC, Univ. Cantabria, Santander Spain
Show AbstractMagnetic Heusler Ni-Mn-(Ga,Sn,In,Sb) shape memory alloys with excess of Mn exhibit a martensitic transformation (MT) accompanied by large and sharp changes of the lattice parameters, entropy, magnetization and resistivity. In these alloys, the magnetic field greatly influences the MT, whereby giant phenomena such as a giant field-induced strain, magnetoresistance and magnetocaloric effect (MCE) are observed at such point.A Ni1.86Mn1.31Sn0.83 Heusler alloy has been fabricated by induction melting and casting, followed by annealing at 900oC for 72h, and subsequent water-quench. DSC, specific heat, cp, and thermomagnetization measurements have shown that this alloy exhibits a Curie temperature at 318 K, a direct MT transformation at Tm = 234K and a reverse one at Ta=253K. According to X-rays and neutrons diffraction, it has a cubic L21-ordered structure (a = 5.976 Å) in the austenitic phase and a modulated orthorhombic structure in the martensitic phase. The influence of the magnetic field on the transformation temperatures was studied by extensive measurements of the temperature dependence of magnetization and cp under constant magnetic fields up to 14 T using a VSM and relaxation technique implemented in a Quantum Design PPMS platform, respectively. Magnetic field-induced linear shifts of Tm, dTm/dB0=-1.50 K/T, and Ta, dTa/dB0 =-1.26 K/T, are obtained for MT, while Curie temperature was proportional to B0^2/3 following the mean-field theory of phase transitions. An unusual low-field maximum on Tm/Ta versus magnetic field is found for the first time. Exchange bias has been observed in the metamagnetic martensitic phase below 50 K. The results are discussed in terms of magnetic clustering and competitive ferro - antiferromagnetic interactions.The cp (T) dependence exhibits a peak at MT and a λ-anomaly at the Curie temperature. The magnetic field-induced shifting of both two anomalies gives rise to a large MCE at TC and large inverse MCE at MT. The peak values of the isothermal magnetic entropy, ΔSm, in the vicinity of MT and TC have been determined from the total entropy to be equal to 3 J/Kmol and -1.5 J/Kmol at 8T, respectively. The former value of ΔSm is within the range of giant values of MCE observed in the manganites. In addition, we found that the Debye temperature and the electronic coefficient are 310±2 K and 16.9±0.3 mJ/K^2mol, respectively, and do not depend on the magnetic field within the indicated uncertainties. The latent heat at MT in zero field was estimated to be 4.5 J/g. The financial supports from Ikerbasque Foundation and Basque Government Department of Education (project IT-347-07) is acknowledged. Assistance of Dr.I. Orúe from SGIker (UPV/EHU) is also appreciated.
10:30 AM - G1.3
Influence of Degree of Order on Magnetic Field-induced Strain in Fe3Pt.
Masataka Yamamoto 1 , Takashi Fukuda 1 , Tomoyuki Kakeshita 1
1 , Osaka University, Suita-shi Japan
Show AbstractMartensite phase of Fe3Pt exhibits a large magnetic field-induced strain (MFIS) of several percent due to the rearrangement of martensite variants under magnetic field. Considering the fact that the martensitic transformation behavior of Fe3Pt is strongly influenced by the degree of order S, we can expect a significant effect of S on the MFIS of Fe3Pt. We prepared two single crystals with different degrees of order of S = 0.48, and 0.75 by changing heat-treatments. The specimen with S = 0.48 transforms to the bct martensite, and the specimen with S = 0.75 transforms to the fct martensite. Magnetization measurements in a single variant state have revealed that the c axis (short axis) of the martensite phase is hard to magnetize compared to a axis for S = 0.48, but vice versa for S = 0.75. A large magnetic field-induced strain due to the rearrangement of martensite variants is observed for S = 0.75 but not for S = 0.48. This difference in MFIS arises from the consequence of difference in uniaxial magnetocrystalline anisotropy constant Ku, twinning shear, and twinning stress between the fct and bct martensites.
10:45 AM - G1.4
Co-Al Ferromagnetic Shape Memory Alloys.
Toshihiro Omori 1 , Keisuke Ando 1 , Kodai Niitsu 2 , Yuji Sutou 1 , Katsunari Oikawa 1 , Ryosuke Kainuma 2 , Kiyohito Ishida 1
1 Department of Materials Science, Graduate School of Engineering, Tohoku University, Sendai Japan, 2 Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai Japan
Show AbstractAlthough the pure Co showing the Curie temperature at 1121°C undergoes martensitic transformation between γ phase (fcc) and ε phase (hcp) by the movement of a/6<112> Shockley partial dislocations at around 400°C, only a slight shape memory (SM) effect can be obtained. Recently, it has been reported that a metastable L12 phase (Co3Al) precipitates in the γ phase of Co-Al alloy with a high Al content (T. Omori et al. Mater. Sci. Eng. A 438-440 (2006) 1045). Such a tendency in atomic ordering seems to assist the reversible atomic movement during the forward and reverse martensitic transformations and to enhance shape memory properties. In this study, the martensitic and magnetic transformations and shape memory properties of the γ Co-Al alloys were investigated. The martensitic and bainitic transformations of β (B2) CoAl will also be presented.The γ/ε martensitic transformation temperatures decrease with increasing Al content and the transformation temperature hysteresis increases from 60°C (0Al ) to 150°C (16at%Al) in the Co-Al system. On the other hand, the SM effect is enhanced by the addition of Al over 10at% and is detected at high temperatures between 200°C and 300°C in the Co-14at%Al alloy. The Curie temperature and the saturation magnetization at 298K for the Co-14 at% Al are 690°C and 120 emu/g, respectively. The shape change controlled by magnetic field gradient may be expected to be used for practical applications.
G2: Metamagnetic Shape Memory Alloys
Session Chairs
Monday PM, November 30, 2009
Hampton (Sheraton)
11:30 AM - **G2.1
Phase Transformations in the Ni-Mn-based Metamagnetic Shape Memory Alloys.
Ryosuke Kainuma 1 , Wataru Ito 1 , Rie Umetsu 1 , Takeshi Kanomata 2 , Kiyohito Ishida 3
1 IMRAM, Tohoku University, Sendai, Miyagi, Japan, 2 Faculty of Engineering, Tohoku Gakuin University, Tagajo, Miyagi, Japan, 3 Dept. Mater. Sci., Tohoku University, Sendai, Miyagi, Japan
Show AbstractThe NiMn-based ordered bcc alloys, such as NiMnIn and NiMnSn alloys, show a unique transformation from a ferromagnetic parent (P) to a weak magnetic martensite (M) phase and that a magnetic field-induced transformation from the M to the P phase appears. Furthermore, the shape memory (SM) effect due to the magnetic-field induced reverse transformation, namely, metamagnetic SM effect, can be obtained using this transition. In these alloys, there are three kinds of transformations, B2/L21 order-disorder transition, magnetic transformation and martensitic transformation, which show some correlations one another. In the presentation, the atomic and magnetic ordering and martensitic transformations in the metamagnetic SM alloys will be reviewed and some recent works performed by our group will be introduced.
12:00 PM - **G2.2
Crystallographic Orientation and Heat Treatment Effect on Magnetic Field-Induced Phase Transformations of NiMnCoIn Metamagnetic Shape Memory Alloys.
Ibrahim Karaman 1 , Burak Basaran 1 , Ruixian Zhu 1 , Haluk Karaca 2 , Yuriy Chumlyakov 3
1 Department of Mechanical Engineering, Texas A&M University, College Station, Texas, United States, 2 Department of Mechanical Engineering, University of Kentucky, Lexington, Kentucky, United States, 3 , Siberian Physical Technical Institute, Tomsk Russian Federation
Show AbstractIn the present work, the magnetic field-induced reversible martensitic transformation in Ni45Mn36.5Co5In13.5 (in at.%) magnetic shape memory alloy (MSMA) single crystals was characterized as a new magneto-structural mechanism responsible for magnetic field-induced strain (MFIS) in MSMAs. This new mechanism demonstrates potential to result in significantly higher work outputs than that of conventional MSMAs such as Ni2MnGa in which field-induced martensite variant reorientation leads to MFIS. The effects of applied field on the phase transformation temperatures, magnetization, and superelastic responses were systematically investigated as a function of crystallographic orientation and heat treatments, and selected results will be presented. The magnetic work output of the NiMnCoIn alloy was determined to be more than 1 MJm^−3 per Tesla, which is one order of magnitude higher than that of the conventional MSMAs. In addition, the work output of NiMnCoIn is orientation independent, potentially surpassing the need for single crystals, and not limited by a critical field, thus by a maximum work output. Transformation strains and magnetostress levels were determined as a function of crystal orientation. The [001] single crystals in solution treated form resulted in 23 MPa/Tesla magnetostress level with transformation strain of more than 6% under compression near room temperature. Using the magnetic properties and structural information from the [100] crystals, we have theoretically shown that crystals with a [111] orientation can demonstrate a magnetostress level of 140 MPa/Tesla with 1.2% strain under compression. The experimental magnetostress values in few [111] crystals, however, were lower than the theoretical levels, on the order of 50 MPa/Tesla. The structural investigations revealed the potential reasons for this discrepancy and indicated that heat treatment and cooling rate after solution treatment plays a significant role on the crystal structure of the transforming phases, and thus, phase transformation temperatures and magnetic properties such as saturation magnetization. It was found that by controlling the cooling rate from solution treatment temperature, it is possible to obtain B2 or L21 austenitic phase or mixture of two, and L10, 6M or mixture of different modulated structures in martensite. Magnetic properties and thus magnetostress levels was found to depend on the structure of the transforming phases.
12:30 PM - G2.3
Hysteresis and Multiferroism in Cobalt Substituted Ni50Mn40Sn10.
Vijay Srivastava 1 , Xian Chen 1 , Richard James 1
1 Aerospace Engg and Mechanics, University of Minnesota, Minneapolis, Minnesota, United States
Show AbstractThe Heusler alloys Ni-Mn-Z (Z=Al, In, Sn, Sb), show a reversible martensitic transformation and unusual magnetic properties. Some examples of these alloys transform from strongly ferromagnetic austenite to a paramagnetic or antiferromagnetic martensite. As is consistent with the Clausius-Clapeyron equation, the martensitic phase transformation can be manipulated by a magnetic field, leading to possible applications of these materials for the magnetic shape memory effect, energy conversion and solid state refrigeration. These systems provide an interesting candidates for the exploration of the effect of compatibility on hysteresis [1,2,3], and lowered hysteresis would be beneficial for the applications mentioned above. By increasing the compatibility between two transforming phases, it has been shown in other cases [2,3] that one can significantly affect the hysteresis. The simplest procedure that has been shown to be relevant for lowering hysteresis is to tune the composition so that the middle eigenvalue λ2 of the distortion matrix equals 1. We report [4] results of such tuning of lattice parameters in cobalt substituted Ni50Mn40Sn10, while simultaneously achieving desirable Curie and martensitic transformation temperatures. Following these procedures we achieve minimum hysteresis for Ni43Co7Mn40Sn10, and we report structural and magnetic properties While the mother alloy Ni50Mn40Sn10 is reported to be non magnetic, the addition of cobalt leads to transition from antiferromagnetic martensite to ferromagnetic austenite and the appearance of a metamagnetic transition. We discuss also the possibility of satisfying further conditions of compatibility in this system. 1.R. D. James and Z. Zhang, A way to search for multiferroic materials with ‘unlikely’ combinations of physical properties, in Magnetism and Structure in Functional Materials (ed., Lluis Manosa, Antoni Planes, Avadh Saxena), Springer Series in Materials Science, vol. 79, Springer-Verlag (2005).2.J. Cui, Y. S. Chu, O. Famodu, Y. Furuya, J. Hattrick-Simpers, R. D. James, A. Ludwig, S. Thienhaus, M. Wuttig, Z. Zhang and I. Takeuchi, Combinatorial search of thermoelastic shape memory alloys with extremely small hysteresis width. Nature Materials 5 (2006), pp. 286—2903.Zhiyong Zhang, R. D. James and Stefan Müller, Energy barriers and hysteresis in martensitic phase transformations, Acta Materialia (Overview), accepted (2009).4.Vijay Srivastava and R. D. James, Hysteresis and multiferroism in cobalt substituted Ni50Mn40Sn10 , in preparation (2009).
12:45 PM - G2.4
Isothermal Martensitic Transformation Kinetics in Ni-Mn-Sn Ferromagnetic Shape Memory Alloys.
Patrick Shamberger 1 , Alexandre Pakhomov 1 , Fumio Ohuchi 1
1 Materials Science & Engineering, University of Washington, Seattle, Washington, United States
Show Abstract
Magnetic field-induced first-order martensitic phase transitions allow for large strain recovery at constant temperature by the metamagnetic shape memory effect [1]. This effect may lead to high-performance magnetic field-controlled actuators and sensors. One of the principle advantages of the metamagnetic shape memory effect is that it is not limited by the rate of thermal diffusion and dissipation, as are classical shape memory materials [2]. However, because the mechanism of strain recovery depends on a phase transformation, the kinetics of that transformation may limit the actuation rate in metamagnetic shape memory alloys. Therefore, a complete understanding of the phase transformation rate of metamagnetic shape memory alloys is important in order to evaluate their potential as actuators and sensors.
Here, we present observations on the time-dependence of the martensitic phase transformation in a suite of Ni-Mn-Sn alloys. We demonstrate that while the martensite to austenite transformation proceeds very rapidly (faster than the time-scale of our observations), the austenite to martensite transformation has a significant isothermal component – up to ~60% transformation over a period of 60 hours. This asymmetry suggests that the martensitic transformation may be nucleation-limited. Furthermore, we demonstrate that the transformation rate is driven primarily by the magnetic Gibbs free energy, and therefore is a function of both temperature and magnetic field [3]. We interpret our results in terms of an activated process with distribution of activation energies and propose a semi-empirical model to predict the extent of phase transformation as a function of time and temperature-magnetic field history.
[1] R. Kainuma et al., Nature, 439, 957-960 (2006).
[2] M.V. Gandhi and B.S. Thompson, Smart Materials and Structures (Chapman & Hall, London, 1992).
[3] P.J. Shamberger and F.S. Ohuchi, Phys. Rev. B., 79, 144407 (2009).
G3: New Aspects of the Ni<sub>2</sub>MnGa System
Session Chairs
Monday PM, November 30, 2009
Hampton (Sheraton)
2:30 PM - **G3.1
Magnetic and Crystallograhic Properties of Ni2MnGa based Alloys.
Klaus-Ulrich Neumann 1 , Kristin Neumann 1 , Kurt Ziebeck 1 , Tilmann Hickel 2
1 Physics, Loughborough University, Loughborough United Kingdom, 2 Department of Computational Materials Design , Max Planck Institut, Duesseldorf Germany
Show AbstractThe ferromagnetic shape memory alloy Ni2MnGa and related compounds have been intensely investigated. The magnetic and crystallographic properties of Ni(2+x)Mn(1-x)Ga compounds and of the isoelectronic alloy series Ni2Mn(1-2x) CrxFexGa are discussed. The notion of the number of valence electrons as a useful parameter for the discussion of changes in alloy series is examined. Structural information is obtained by neutron scattering. The low and high temperature phases are identified and characterised. The changes in the low temperature martensitic phase are examined as a function of alloying. The role of lattice distortions and defects is highlighted for determining low temperature crystallographic phase.
3:00 PM - G3.2
Effect of High Magnetic Field on Premartensitic Transition in Ni-Mn-Ga Alloys.
Jose Barandiaran 1 , Jon Gutierrez 1 , Volodymyr Chernenko 1 , Patricia Lazpita 1 , Jorge Feuchtwanger 1
1 Electricidad y Electronica, University of Basque Country, Leioa Spain
Show AbstractIt is well known that in the close-to-stoichiometric Ni2MnGa alloys, a premartensitic lattice instability evolves during cooling, and freezing of a soft mode with a wave vector q = [0.3, 0.3, 0](2π/a) occurs at some temperature TI , giving rise to a weekly first-order transition between the initial cubic phase and the modulated soft-mode condensed one. The cause of such phonon softening and condensation is still under intense study. Particularly, the influence of the magnetic field on TI was studied in several works but the results appear not conclusive.In order to clarify the premartensitic transition sensitivity to the applied magnetic field, we have performed precise measurements of the temperature dependence of resistivity under constant magnetic fields up to B0=14 T, using both polycrystalline (PC) and single crystalline (SC) Ni2MnGa alloys as model compounds. A low-field minimum on the transition temperature versus magnetic field dependence with a subsequent linear increase at high field is found in both alloys. The minimum is attributed to the magnetic anisotropy contribution to the Clausius-Clapeyron relationship, which describes the premartensitic transition. This contribution is confirmed by magnetization loops measurements. The slopes of the high field linear dependence of TI versus B0 were determined to be 0.55 and 0.27 K/T for PC and SC samples, respectively. These figures allow estimating the corresponding magnetization jumps at the transition as 0.32 and 0.17 Am^2/kg. The obtained data represent an important input to the theoretical modeling of the soft-mode condensation in the ferromagnetic media.
3:15 PM - **G3.3
Recent Development of the Magnetic Shape Memory Research in Finland.
Outi Soderberg 1 , Ilkka Aaltio 1 , Yanling Ge 1 , Alexandr Soroka 1 , Raisa Niemi 1 , Xuwen Liu 1 , Simo-Pekka Hannula 1
1 Department of Materials Science and Engineering, Helsinki University of Technology, Espoo Finland
Show AbstractNi-Mn-Ga based magnetic shape memory (MSM) materials have been studied in Finland at TKK since 1998. The large HUT-MSM-project resulted in several noteworthy discoveries, such as MSM-alloys with high service temperature, 10% field-induced-strain, several rules on when and how a Ni-Mn-Ga alloy is able to exhibit this phenomenon. Since the finish of the first MSM project in 2003, TKK research has been targeted to a few specific fields. Emphasis has been given to deepening the understanding of the structure and behavior of twin boundaries, and their role in the damping polymer composites. Twin boundary studies have been carried out by XRD and the high-resolution transmission electron microscopy (HRTEM). In-situ straining of Ni-Mn-Ga single crystals in TEM has been carried out in co-operation with the Institute of Physics in Prague, Czech. These studies have given further insight to the twinning mechanisms in NM martensites. Furthermore, the results obtained by neutron diffraction in co-operation with Institute for Metal Physics, Kiev, and ILL, Grenoble, have also given new crystallographic information. Research has been carried out also for searching alloys that can widen the stabile thermal property range of the MSM materials: alloys having a profound MSM effect temperature range being otherwise stable down to 4 K, have been established. Furthermore, modeling based on Ginsburg-Landau theory has been applied to evaluate aging and thermal fluctuations in the modulated Ni-Mn-Ga structures. However, as the main interest in the Finnish MSM research has been in the applied research, a lot of emphasis has been put on the service properties of these materials. Damping of Ni-Mn-Ga polymer composites has been proved to be excellent at high stiffness levels with the loss factor δ = 0.6 at E ≈ 1 GPa. In the fabricated polymer composites also sensing properties have been demonstrated showing promise for the use of these materials in sensor applications. Most of the efforts have been placed on the study of the long-term behavior of the MSM elements in the actuation. This basic information is still largely missing. So far, a fatigue life of 1x109 has been recorded for a five-layered modulated Ni-Mn-Ga structure. The evolution of the MSM parameters during the long-term actuation is recorded and they are used as input data for the models developed in the European MAFESMA co-operation.As a commercial target, Adaptamat Ltd develops technology to produce Ni-Mn-Ga magnetic shape memory material with improved quality, lower twinning stress, longer fatigue life as well as lower cost and better availability for use in research and development.
3:45 PM - G3.4
Effects of Surface Preparation and Mechanical Training on Twinning Stress of Ni-Mn-Ga Single Crystals.
Markus Chmielus 1 2 , Katharina Rolfs 1 , Cassie Witherspoon 2 , Nikki Kucza 2 , Walter Reimers 3 , Peter Muellner 2 , Rainer Schneider 1
1 GI-1, Helmholtz Centre Berlin for Materials and Engery, Berlin Germany, 2 Materials Science and Engineering, Boise State University, Boise, Idaho, United States, 3 Institut für Werkstoffwissenschaften und –technologien, Technische Universität Berlin, Berlin Germany
Show AbstractAchieving low twinning stresses, which requires highly mobile twin boundaries, is essential for the magnetic field driven shape change of magnetic shape memory alloys (MSMA). Surface preparation as part of the sample production influences the mechanical properties of MSMA. In this work, specimens were cut with spark erosion cutting, which is commonly used for Ni-Mn-Ga sample preparation. This cutting method produces a rough surface layer. Directly after cutting, Ni-Mn-Ga single crystals exhibit a high twinning stress. So far, the increased twinning stress of unpolished samples was attributed to defects in the surface layer. To characterize the impact of electro polishing on twinning stress, one sample set was electro polished and mechanically trained several times while a control set was trained without being electro polished. After each electro polishing and training step, the twinning stress reduces significantly. The stress-strain curves displayed significant serrations. The control set of unpolished samples shows a similar reduction of the twinning stress after each training step. In this case, however, the stress-strain curves are very smooth and a significant hardening sets in at higher strain (above 50% of the maximum strain). Comparing both sample groups, it is shown here that a reduction of the twinning stress is due to the mechanical training rather than the electro polishing. After these tests, the surface layer of the unpolished single crystals was mechanically removed, resulting in a reduction of the observed hardening in higher strain regions to nearly zero. For trained and mechanically polished samples, the twinning stress stayed at a very low level over the entire twinning strain range. Mechanical polishing reduces the twinning stresses especially in higher strain ranges in addition to the softening, which is due to mechanical training.
G4: Theory of Magnetic Shape Memory Alloys
Session Chairs
Monday PM, November 30, 2009
Hampton (Sheraton)
4:30 PM - **G4.1
New Functional Magnetic Shape Memory Alloys fromFirst-Principles Calculations.
Peter Entel 1 , Antje Dannenberg 1 , Markus Gruner 1 , Manfred Wuttig 2
1 Physics Department, University of Duisburg-Essen, 47048 Duisburg Germany, 2 Department of Materials Science, University of Maryland, College Park, MD 20742, Maryland, United States
Show AbstractAn overview will be given of new ferromagnetic Heusler alloys like Ni-Co-(Al, Ga, Zn) and Fe-Co-(Al, Ga, Zn) [1] or alloys arising from mixing of magnetic shape memory and spintronics materials [2] by comparison with today's mostly investigated systems, Ni-Mn-Z (Z = Al, Ga, In, Sn, Sb). For the new alloys, the valence electron number per atom varies between e/a = 6.75 (Fe2CoZn) and e/a = 8 (Ni2CoAl). The investigations are based on first-principles as well as Monte Carlo simulations. A detailed study of atomic structure, magnetism and electronic properties compared with corresponding features of prototypical Ni-Mn-Z materials shows that some of the new systems may have rather high Curie and martensitic transformation temperatures and may be distinguished for devices which exploit the magnetic shape memory effect. The magnetic behavior and high Curie temperatures are inferred from Monte Carlo simulations while the structural instability is obvious from local minima in the ab initio total energy curves as a function of tetragonal distortion. Supercell calculations show the tendency towards phonon softening in the austenitic phase above the martensitic transformation temperature, although the intability seems to arise mostly from electronic driving forces, which are enhanced by the low-energy lattice vibrations. [1] T. Takayama, S. Shinohara, K. Ishida, and T. Nishizawa, J. Phase Equlibria 16, 390 (1995).[2] P. Entel, M.E. Gruner, A. Dannenberg, M. Siewert, S.K. Nayak, H.C. Herper, and V.D. Buchelnikov, Contribution to 2nd International Conference on Ferromagnetic Shape Memory Alloys, July 1-3, 2009, Bilbao (Spain).
5:00 PM - **G4.2
A Mesoscopic Free Energy Approach for Thermo-Magneto-Mechanically Coupled Behavior of Magnetic Shape MemoryAlloys.
Stefan Seelecke 1 , Phillip Morrison 1
1 Department of Mechanical & Aerospace Engineering, North Carolina State University, Raleigh, North Carolina, United States
Show AbstractMotivated by the recent development of thin-film NiMnGa actuators, Kohl et al. [1,2], which, in contrast to conventional FSMA actuators, are driven by the Joule heating of an electric current, this paper presents a fully coupled thermo-magneto-mechanical model for magnetic shapememory alloys.A model for the macroscopic behavior of such materials is developed by mapping micro-scale mechanisms into a mesoscopic free energy formulation, which will subsequently be used to predict switching effects and phase transitions between different martensitic variants and austenite on the one hand and between ferromagnetic and paramagnetic states on the other.Based on the above free energy function, the transformations are formulated as time-dependent evolution laws motivated by the theory of thermally activated processes using standard arguments from Boltzmann statistics for the transition probabilities. The macroscopic behavior is obtained by suitable averaging procedures of magnetization and strain and naturally reproduces the hysteretic fully-coupled multi-field behavior.The model is finally validated by comparison to experiments from Straka et al. [3-5].[1] M. Kohl, D. Brugger, M. Ohtsuka, T. Takagi, 2004, A novel actuation mechanism on thebasis of ferromagnetic SMA thin films, Sensors and Actuators A, 114, pp. 445-450[2] M. Kohl, S. Hoffmann, Y. Liu, M. Ohtsuka, T. Takagi, 2003. Optical scanner based on aNiMnGa thin film microactuator, J.Phys.IV France, 112, pp. 1185-1188[3] Straka, L. and Heczko, O. Superelastic Response of Ni-Mn-Ga Martensite inMagnetic Fields and a Simple Model. IEEE Transactions on Magnetics 39(5), 3402-3404, 2003.[4] Straka, L., Heczko, O., Novák, V., and Lanska, N. Study of austenite-martensitetransformation in Ni-Mn-Ga magnetic shape memory alloy, Journal de Physique IV 112,911-915, 2003.[5] Straka, L., Heczko, O., and Hannula, S.-P. Temperature dependence of reversiblefield-induced strain in Ni-Mn-Ga single crystal. Scripta Materialia 54, 1497-1500, 2006.
5:30 PM - G4.3
Systematic Search of New Ferromagnetic Fe-Ni-Co-Zn-Ga Shape Memory Alloys by ab initio Investigations.
Antje Dannenberg 1 , Markus Gruner 1 , Peter Entel 1 , Manfred Wuttig 2
1 , University of Duisburg-Essen, Duisburg Germany, 2 Department of Materials Science and Engineering, University of Maryland, College Park, MD 20742, Maryland, Maryland, United States
Show AbstractIn order to enhance the potential for technological applications of magnetic shape memory alloys (MSMA), higher operating temperatures are required. The currently used ferromagnetic Heusler systems still have too low Curie temperatures as well as martensitic transition temperatures. Within this contribution we present results of a detailed study of electronic, structural and magnetic properties of various systems based on Fe-Ni-Co-Zn-Ga by using ab initio and Monte Carlo simulations. The new materials may be promising candidates for future magnetic shape memory alloys as our results promise rather high Curie temperatures and martensitic transformation temperatures. By calculating energy differences between structural and magnetic phases, tendencies of martensitic and magnetic phase transition temperatures of the new Zn-based Heudler systems may be predicted.
5:45 PM - G4.4
Ab initio Super-cell Calculations of Fe-based Magnetic Shape Memory Alloys.
Markus Gruner 1 , Peter Entel 1
1 Department of Physics, University of Duisburg-Essen, Duisburg Germany
Show AbstractThe face centered tetragonal phases of disordered off-stoichiometric Fe70Pd30 and ordered Fe3Pt exhibit considerable magnetic shape memory (MSM) behavior as it is observed for the widely discussed full Heusler system Ni-Mn-Ga. However, while showing the better mechanical properties, the martensitic transition temperatures of the Fe-based systems are far too low for practical application but addition of further components may help to stabilize the desired fct phase at ambient conditions. The prediction of suitable elements requires a proper understanding of the mechanisms leading to the martensitic transformation.Within this contribution we provide as a first step a comparison between stoichiometrically ordered Fe3Pd and disordered Fe-Pd alloys. First principles methods within the framework of density functional theory allow the determination of structural and electronic properties on the atomistic level and therefore ideally complement experimental investigations while the link to the electronic structure will help to understand the relevant properties and to predict improved materials. The disorder is modeled either implicitly within the coherent potential approximation (CPA) assuming the ideal lattice positions as well as explicitly within a super-cell approach. While being computationally expensive, the latter approach offers a straightforward way to take into account the relaxation of the atomic positions as a consequence of the chemical environment. Our calculations demonstrate that indeed local distortions provide an important contribution to the variation of the total energy along the Bain-path and are thus decisive for the correct description of the binding surface. In the light of these findings, possible candidates for ternary systems with improved MSM properties are discussed.This work is supported by the Deutsche Forschungsgemeinschaft through SPP 1239. Part of the calculations were carried out on the supercomputers of the John von Neumann Institute for Computing, Forschungszentrum Jülich.
Symposium Organizers
Eckhard Quandt University Kiel
Manfred Wuttig University of Maryland
Tomoyuki Kakeshita Osaka University
Sebastian Faehler IFW Dresden
G5: Twins, Modulations and Their Mobility in MSMA
Session Chairs
Tuesday AM, December 01, 2009
Hampton (Sheraton)
9:30 AM - **G5.1
Deformation of Hierarchically Twinned Martensite.
Peter Mullner 1 , Alexander King 2
1 Materials Science and Engineering, Boise State University, Boise, Idaho, United States, 2 , The Ames Laboratory, Ames, Iowa, United States
Show AbstractShape-memory alloys deform via the reorganization of a hierarchically twinned microstructure. In multiply-twinned microstructures of self-accommodated martensite, twin boundaries themselves present obstacles for twin boundary motion. In spite of a high density of obstacles, twinning occurs at a stress of only a few megapascal in self-accommodated martensite of Ni-Mn-Ga Heusler alloy single crystals. Neither atomistic nor dislocation based models account for such low yield stresses. Twinning mechanisms are studied here on a mesoscopic length scale making use of the disclination theory. Two approaches are taken where first a strictly periodic twin pattern is considered. Such microstructures contain periodic disclination walls with optimally screened stress fields and, thus, low strain energy density. The requirement for strict periodicity implies that the twin microstructure reorganizes homogeneously on a mesoscopic scale. The stress required for reorganization is obtained within the disclination quadrupole approximation. In a second approach, the condition of strict periodicity is somewhat relaxed. A discontinuity of the density of secondary twins is introduced and modeled as a disclination dipole or a superdislocation. The stress required for nucleation of this dipole is larger than the stress required for homogeneous reorganization. However, once the discontinuity is formed, it can move under a much smaller stress, which is in agreement with experimental findings.
10:00 AM - G5.2
Geometrically Constrained Metastable Modulated Martensite.
Stefan Kaufmann 1 2 , Ulrich Roessler 1 , Manfred Wuttig 3 , Robert Niemann 1 2 , Oleg Heczko 4 , Joerg Buschbeck 1 , Thomas Thersleff 1 , Ludwig Schultz 1 2 , Sebastian Faehler 1 2
1 , IFW Dresden, Dresden Germany, 2 Department of Physics, University of Technology, Dresden Germany, 3 Department of Material Science & Engineering, University of Maryland, College Park, Maryland, United States, 4 Institute of Physics, Academy of Science of Czech Republic, Prague Czechia
Show AbstractModulated phases occur in numerous functional materials like ferroelectrics and magnetic shape memory alloys. In order to understand the origin and consequences of this modulation, we examine the Ni-Mn-Ga magnetic shape memory alloy. We show that, according to the concept of adaptive martensite by Khachaturyan et al. [1], the modulated 14M martensite phase in Ni-Mn-Ga fulfils all requirements for an adaptive phase . In this approach, the 14M modulated martensite can be constructed from nanotwinned variants of the non-modulated (NM) martensite phase. In XRD diffraction patterns this nanotwinned structure appears as an orthorhombic phase [2], as already suggested by Pons et al. on the basis of high-resolution transmission electron microscopy imaging [3]. By means of epitaxial films, we could confirm this concept by integral XRD measurements and probe the transformation path in detail. The substrate constraint results in films where austenite, 14M and nonmodulated (NM) phases coexist over a very broad temperature range, while the corresponding (inter-)martensitic transitions in bulk are commonly sharper and completed in a narrow temperature interval. Using the rigid substrate as a reference frame we evaluated the transformation matrix from austenite to adaptive 14M martensite and show that the orientations of the 14M martensite variants agree with the Wechsler-Lieberman-Read theory. Pole figure measurements were used to demonstrate that the orientation of macroscopic NM variants is identical to the orientation of nanotwinned NM variants forming the 14M adaptive martensite phase. Combining the concept of adaptive martensite with branching of twin variants, we can extrapolate physical properties of the 14M phase from the properties of the NM martensite building blocks, e.g. the magnetocrystalline anisotropy of 14M, which agrees with measurements. The branching mechanism is directly visualized by cross section SEM micrographs prepared by Focused Ion Beam (FIB) cuts. Temperature dependent XRD measurements prove the pseudo-orthorhombic 14M phase not to be an intermediate, thermodynamically stable phase but an adaptive phase stabilized by the constraint of the substrate. Finally the coexistence of different martensite phases leads to characteristic orientations for phase boundaries and macroscopic twin boundaries. This complex microstructure is probed down to the nm range by high resolution SEM and AFM and explained by a compatible microstructure of the NM martensite.[1] Khachaturyan A.G. et al., Phys. Rev. B 43, (1991) 10832[2] Wang Y.U., Phys. Rev. B 74, 104109 (2006) [3] Pons J., Chernenko V.A, Santamarta R., Cesari E., Acta mater. 48, (2000) 3027
10:15 AM - G5.3
Compositional Dependence of Transformation Sequnce in NiMnGa Alloys.
Minoru Nishida 1 , Shingo Nakamura 1 , Masaru Itakura 1
1 , Kyushu Univerisity, Kasuga, Japan
Show AbstractIt has been reported that Ni-Mn-Ga alloys show a large change in the magnetic moment associated with a thermoelastic martensitic transformation from the L21 parent structure to 10M with the stacking sequence (3-2)2, 14M with the stacking sequence (5-2)2 or 2M with the stacking sequence (1)2 martensitic phases. The 10M and the 14M martensites can be characterized by a five-layered modulated structure and a seven-layered modulated structure, respectively. The 2M martensite is a non-modulated structure. It has been confirmed that there are several transformation sequences in Ni-Mn-Ga alloys depending on their composition such as P → I → 10M, P → 14M → 2M and P→ 2M, where I is the intermediate phase which has a six-layered modulated structure. However, no systematic study has been completed on the compositional dependence of transformation sequence. In the present study, we have prepared Ni50Mn25+XGa25-X alloys with X = 0 ~ 5. Their transformation sequence has been mainly investigated by in-situ heating and cooling TEM observations. Some of novel findings in the present study are summarized as follows:1) There are two new incommensurate phases of 10M’ and 14M’ corresponding to the 10M and the 14M, respectively.2) There is new intermediate phase of 14M with an eight-layered modulated structure.3) The variant boundary of the I-phase with a six-layered modulated structure has been observed for the first time.The morphological aspects during the transformation are also discussed on the basis of TEM observations.
10:30 AM - **G5.4
Determination of Twin Mobility in Composites.
Jorge Feuchtwanger 1 , Jose Barandiaran 1 , Patricia Lazpita 1 , Jon Gutierrez 1 , Jon Aurrekoetxea 2 , Javier Zurbitu 2 , Vilas Jose 3 , Volodymyr Chernenko 1
1 Electricidad y electronica, Universidad del Pais Vasco, Leioa, Vizcaya, Spain, 2 Mechanical and Manufacturing Department, Mondragon Goi Eskola Politeknikoa, Mondragon, Gipuzkoa, Spain, 3 Quimica Fisisca, Universidad del Pais Vasco, Leioa, Vizcaya, Spain
Show AbstractThe high mobility of twin boundaries in Ferromagnetic Shape Memory Alloys (FSMAs) is responsible for the field-induced strain they can exhibit while in the martensite phase, but this high mobility has also a large internal friction associated to it. While a drawback for actuators, the loss can be used to an advantage to absorb mechanical vibration. The use of composites, has a series of advantages over the use of single crystals for this application; they are less brittle and lighter than the single crystals, while still being able to dissipate a large fraction of the mechanical energy they are subjected to. The composites are fabricated by mixing particles of Ni–Mn–Ga with a polymeric matrix and placing them under a magnetic field while the matrix cures. The magnetic field aligns the particles in chains, and the high magneto-crystalline anisotropy of the particles causes them orient so that the easy axis is parallel to the applied field. We will show through different types of measurements that the mobility of the twin boundaries can be inferred form magnetic measurements and that that inference can be confirmed by the use of diffraction techniques. This has been done both under static conditions, where the pseudoplastic deformation of the particles can be seen, and also under dynamic conditions where it can be seen that the texture of the crystal dynamically follows the stress on the sample. The last part of the talk will show how the composites can respond both to low frequency deformation, but also to higher frequencies like the ones that correspond to impact loading conditions.
G6: Twins and Domains in MSMA
Session Chairs
Tuesday PM, December 01, 2009
Hampton (Sheraton)
11:30 AM - **G6.1
Observation of Magnetic Domain and Twin Boundary Dynamics in Magnetic Shape Memory Alloys.
Jeffrey McCord 1
1 , IFW Dresden, Dresden Germany
Show AbstractThe investigation of magnetic field induced strain during fast reorientation process provides vital information for the optimization of the properties for future devices in magnetic shape memory alloys (MSMAs). Using a dynamic actuation experimental set-up, the magnetic field induced reorientation of crystallographic and magnetic domains is imaged directly up to frequencies approaching the dynamic limit of MSMAs. The results provide significant information of twin boundary performance during static and high frequency actuation and give important input to the refinement of already existing models of twin boundary motion. From static magnetic surface domain imaging of different surfaces, using a magneto-optical indicator film technique (MOIF), a clear relation between surface and volume domains of NiMnGa MSMA single crystals is derived. With the occurrence of a twin boundary, the twin boundary acts as a magnetic domain mirror inside the MSM material. Starting from this analysis, it is demonstrated that a reorganization of the magnetic domains is not required for the occurrence of twin boundary motion. Based on these results, the actuation performance of different MSMAs single crystals at various excitation frequencies up to 600 Hz as well as corresponding pulse field applications is presented. Reversible twin boundary motion activated in the frequency range up to 600 Hz, respectively below 1 ms rise-time is observed. Independent of the dynamic excitation, the same onset of strain with field is found. The maximum field-induced twin-boundary motion increases with actuation frequency. Possible origins of the enhancement based on local eddy current heating at the twin-boundary are discussed. Moreover, a memory of increased twin boundary mobility over several hours occurs. Therefore a local temperature rise as the solely origin for enhanced twin boundary mobility can be neglected. From the observed after-effects and the long-term relaxation in the twin boundary mobility occurring following the dynamic experiments, additional accommodation contributions play an essential role in twin boundary dynamics. A consideration of all possible and simultaneously occurring contributions to the twin boundary mobility will be given.
12:00 PM - G6.2
Finite-temperature Anisotropic Elastic Properties of Ni-Mn-In Magnetic Shape Memory Alloy.
Kristen Williams 1 2 , Tahir Cagin 2 1
1 Materials Science & Engineering Graduate Program, Texas A&M University, College Station, Texas, United States, 2 Department of Chemical Engineering, Texas A&M University, College Station, Texas, United States
Show AbstractDesigning magnetic shape memory materials with practicable engineering applications requires a thorough understanding of their electronic, magnetic, and mechanical properties. Experimental and computational studies on such materials provide differing perspectives on the same problems, with theoretical approaches offering fundamental insight into complex experimental phenomena. Many recent computational approaches have focused on first-principles calculations, all of which have been successful in reproducing ground-state structures and properties such as lattice parameters, magnetic moments, electronic density of states, and phonon dispersion curves. With all of these successes, however, such methods fail to include the effects of finite temperatures, effects which are critical in understanding how these properties couple to the experimentally-observed martensitic transformation. To this end, we apply the quasi-harmonic theory of lattice dynamics to predict the finite-temperature mechanical properties of Ni-Mn-In magnetic shape memory alloy. We employ first-principles calculations in which we include vibrational contributions to the free energy. By constructing a free energy surface in volume/strain space, we are able to evaluate key thermodynamic properties such as entropy, enthalpy, and specific heat. We further report the temperature dependence of the elastic constants for the austenite and martensite phases and evaluate their role as a driving force for martensitic transformation.
12:15 PM - G6.3
A Study of Magnetomechanical Switching in Ferromagnetic Shape Memory Alloys.
Vesselin Stoilov 1
1 MAME, University of Windsor , Windsor, Ontario, Canada
Show AbstractA continuum thermodynamics formulation for micromagnetics coupled with mechanics is devised to model the evolution of magnetic domain and martensite twin structures in ferromagnetic shape memory alloys. The theory falls into the class of “sharp-phase-front” modeling approaches. In addition to the standard mechanical and magnetic balance laws, a continuity of the chemical potential is postulated. Nucleation of variants and propagation of twin boundaries were investigated under combined magneto-mechanical loading and compared to recent experiments. The analysis demonstrated that phase boundary motion results in significant deformation and allowed estimation of the overall deformation in a ferromagnetic shape memory material. It has been shown that the overall deformation in ferromagnetic shape memory alloys is accompanied by evolution of particular domain patterns. The choice of such configurations is dictated by the requirement that domains remain compatible during evolution, giving rise to a low-energy path for the overall switching. The construction of these patterns is achieved using multirank laminates. Finally, numerical solutions are presented to investigate the fundamental interactions between the magnetic domain wall and the martensite twin boundary in ferromagnetic shape memory alloys.
G7: Caloric Properties of MSMA
Session Chairs
Tuesday PM, December 01, 2009
Hampton (Sheraton)
2:30 PM - **G7.1
Multicaloric Effects in Magnetic Shape Memory Alloys.
Lluis Manosa 1 , Antoni Planes 1 , David Gonzalez-Alonso 1 , Maria Barrio 2 , Erell Bonnot 2 , Josep-Lluis Tamarit 2 , Seda Aksoy 3 , Mehmet Acet 3
1 Facultat de Fisica, Universitat de Barcelona, Barcelona, Catalona, Spain, 2 Fisica i Enginyeria Nuclear, Universitat Politecnica de Catalunya, Barcelona Spain, 3 Experimentalphysik, Universitaet Duisburg-Essen, Duisburg Germany
Show AbstractNi-Mn-based Heusler alloys exhibit an interesting variety of functional properties such as magnetic shape memory, magnetic superelasticity, giant magnetocaloric effects, magnetoresistance and kinetic arrest, among others. All of these properties are a direct consequence of the martensitic transition undergone by these materials within a certain compositional range. The coupling between different degrees of freedom (eg. structural and magnetic) enables the transition to be induced by tuning different external control parameters such as temperature, stress and magnetic field. While conventional shape-memory properties are typically related to uniaxial stresses, application of magnetic fields leads to magnetic shape-memory properties along with magnetocaloric and magnetoresistive functional properties. In the present talk we will explore the effect of an alternative external control parameter: hydrostatic pressure. It will be shown that relatively large entropy changes result from an isothermal pressure application. A comparison between the barocaloric effects arising from hydrostatic pressure and the largely studied magnetocaloric effects will be given.
3:00 PM - G7.2
The Magnetocaloric Effect and Martensitic Variant Reorientation in Ferromagnetic Ni-Mn-Ga Thin Films.
Yuepeng Zhang 1 , Robert Hughes 2 , John Preston 2 3 , Gianluigi Botton 1 2 , Marek Niewczas 1 2
1 Materials Science and Engineering Department, McMaster University, Hamilton, Ontario, Canada, 2 Brockhouse Institute for Materials Research, McMaster University, Hamilton, Ontario, Canada, 3 Department of Engineering Physics, McMaster University, Hamilton, Ontario, Canada
Show AbstractEpitaxial films of the magnetic shape memory alloy Ni–Mn–Ga have been deposited on (001) YSZ substrates using the pulsed laser deposition technique. The films show a well-defined reversible martensitic transformation that coincides with a ferromagnetic ordering of the austenitic phase. The overlapping transitions give rise to a large magnetocaloric effect which is particularly strong at low fields. The effect yields a magnetic entropy change as large as ΔS=1.4 J/kg-K for a magnetic field interval of only 0.5 T. Distinctive to the current observations is the fact that the maximum magnetic entropy change occurs for temperatures where equal percentages of the austenite and martensite phases coexist. The entropy change shows a 3 K temperature hysteresis between the cooling and heating sequences, a feature inherited from the first-order martensitic phase transformation. Associated with this hysteresis is a peak height that is significantly larger for the cooling sequence, an effect attributed to a more highly developed ferromagnetic ordering in the austenite phase at the peak temperature. The films also exhibit a magnetically induced reorientation of the martensitic variants, i.e. the MIR effect, which shows self-activated reversibility. The reversibility is a feature unique to these films, which originates from a magnetic domain structure comprised of MIR-active and MIR-inactive twin variants. The MIR-active variants are responsible for the detwinning, while the MIR-inactive variants exert a restoring force on the MIR-active variants during their reorientation. The results demonstrate that the magnetic domain structure formed in the films is inherited from a substrate induced crystallographic texture and microstructure, which suggests that a tailored MIR response could prove possible through an optimization of the film texture and microstructure.
3:15 PM - G7.3
Magnetocaloric Effect in Ni-Mn-Ga and Ni-Co-Mn-In Heusler Alloys.
Vasiliy Buchelnikov 1 , Mikhail Drobosyuk 1 , Vladimir Sokolovskiy 1 , Sergey Taskaev 1 , Viktor Koledov 2 , Vladimir Khovaylo 2 , Vladimir Shavrov 2
1 , Chelyabinsk State University, Chelyabinsk Russian Federation, 2 , Institute of radioengineering and electronics of RAS, Moscow Russian Federation
Show AbstractThe magnetocaloric effect (MCE) is the ability of magnetic materials to heat up or cool down when placed in or removed from an external magnetic field. It has great importance in the technology of magnetic refrigeration. The magnetic materials with large values of MCE can be applied as work bodies of magnetic cooling devices such as industrial and household refrigerators, air conditioners, heat pumps and etc. Recent experimental study have shown that the Heusler Ni-Mn-X alloys are attractive for the application in magnetic refrigeration. Moreover these alloys have unique properties such as the shape memory effect, the large magnetostriction, the large magnetoresistence and etc. Recent in Ni-Mn-X alloys were experimentally observed two types of MCE. There are negative MCE (DT<0) and positive MCE (DT>0) at the coupled metamagnetostructural (metaMS) phase transitions and magnetic one, respectively.In this work we study experimentally positive and negative MCE of Heusler Ni-Mn-X compounds undergoing magnetic and first order metaMS phase transitions. We have made the magnetocaloric measurements by using a Magnetocaloric Measuring Setup (MMS) produced by Advanced Magnetic Technologies and Consulting Ltd (AMT&C). In this setup adiabatic temperature change (DT) was measured by a direct method. The thermocouple junction was fixed directly on the sample, which was rigidly fastened to the sample placed on a fluoroplastic pad on a sample holder made from nonmagnetic metal. The sample holder was located in a chamber also made from non magnetic stainless steel and the chamber was sealed so the sample did not touch its sides. The magnetic fields (up to 2 T in the MMS) are created by a Halbach permanent magnet magnetic field source. Magnetic field was measured by a Hall probe. The thermocouple and the Hall probe signal were recorded simultaneously, which allowed measuring DT versus magnetic field strength (H). The temperature was changed by an electric heater. The next samples were prepared by arc melting: Ni45Co5Mn36.5In13.5, Ni2+xMn1-xGa (x=0.33, 0.36, 0.39). From experimental magnetic susceptibility results of Ni45Co5Mn36.5In13.5 we have obtained two phase transition temperatures: metaMS temperature is 255 K and the Curie one (Tc) is 400 K. Our MCE measurements of Ni45Co5Mn36.5In13.5 have shown that the maximum value of the negative MCE is 1.65 K at metaMS transition temperature T=255 K at ΔH=2 T. Because of the working range of our MMS from 78 till 370 K, we could not determine the maximum value of positive MCE at the Curie temperature.Also we have measured MCE of Ni2+xMn1-xGa (x=0.33, 0.36, 0.39) upon variation of the magnetic field DH=2 T. Our MCE results at Curie temperature are presented in Table 1.
3:30 PM - G7.4
Comparative Study of the Magnetocaloric Properties in Ni-Mn-X (X = Ga, In, Sn) by Magnetization and Specific Heat Measurements.
Vladimir Khovaylo 1 , Val Novosad 2 , K. Skokov 3 , H. Miki 4 , R. Kainuma 5 , G. Wang 6 , E. Palacios 6 , J. Bartolome 6 , R. Burriel 6
1 , Institute of Radioengineering and Electronics, Moscow Russian Federation, 2 Materials Science Division, Argonne National Laboratory, Argonne, Illinois, United States, 3 Faculty of Physics, Tver State University, Tver Russian Federation, 4 Institute of Fluid Science, Tohoku University, Sendai Japan, 5 Institute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai Japan, 6 CSIC, Universidad de Zaragoza, Zaragoza Spain
Show AbstractRecently, a considerable interest has been paid to magnetocaloric properties of novel ferromagnetic shape memory alloys Ni-Mn-X (X = Ga, Sn, In). Due to the difference in exchange interactions of the parent austenitic phase and the product martensitic phase, a peculiar transformation sequence from paramagnetic low-temperature phase to a ferromagnetic high-temperature phase can be realized in Ni-Mn-X (X = Sn, In) alloys of certain chemical compositions. This coupled magnetostructural phase transition is reversible on subsequent cooling and shows rather a small (~6 K) temperature hysteresis. Reported values of the isothermal magnetic entropy change ΔSm accompanying this first-order phase transition imply that |ΔSm| is comparable to or exceeds that of Gd5(Si1-xGex), La(Fe1-xSix)13, and other related compound demonstrating giant magnetocaloric effect. Judging by these reports, Ni-Mn-X are perspective materials for the use in the technology of room-temperature magnetic refrigeration. However, it must be noted that the isothermal magnetic entropy change in Ni-Mn-X has been evaluated using Maxwell relation which, strictly speaking, has limited applicability in the case of first-order transitions. In order to shed a light on this issue we undertook a comparative study of the magnetocaloric properties of Ni-Mn-X (X = Ga, Sn, In) by means of magnetization and specific heat measurements. Isothermal magnetic entropy change calculated from isofield [M(T)] and isothermal [M(H)] magnetization curves using Maxwell relation was compared with that obtained from temperature dependencies of specific heat. The experimental results clearly showed that ΔSm calculated from the specific heat data is lower then that estimated from the magnetization measurements.
3:45 PM - G7.5
Magnetocaloric Properties of Rapidly Solidified Ni51.1Mn31.2In17.7 Heusler Alloy Ribbons.
Jose Sanchez Llamazares 1 , Blanca Hernando 1 , Victor Prida 1 , Carlos Garcia 2 , Caroline Ross 2
1 Departamento de Fisica, Universidad de Oviedo, Oviedo, Asturias, Spain, 2 Dept. Material Science and Engineering, MIT, Massachusetts, Massachusetts, Massachusetts, United States
Show AbstractHeusler alloys in the Ni50Mn50-xInx system can be obtained as single-phase materials by rapid solidification using melt spinning technique [1]. In present contribution we report the basic magneto-structural and magnetocaloric properties of as-quenched Ni51.1Mn31.2In17.7 ribbons produced by this method. Samples were obtained in argon atmosphere with a surface speed of the copper wheel of 48 m/s. X-ray powder diffraction, scanning electron microscopy with energy dispersive spectroscopy microanalysis and magnetization measurements were used to characterize phase constitution, microstructure, average elemental chemical composition and magnetic properties. The ribbon flakes produced were fully crystalline with the following dimensions: 9-12 μm in thickness, 1.5-2.0 mm in width and 5-12 mm in length. The alloy crystallized in a ferromagnetic cubic austenite with the ordered L21-type crystal structure (a=0.5989(3) nmm at 250 K) and Curie temperature of TC=275 K. A similar phase constitution was previously reported for bulk alloys with 16 < x ≤ 20 produced by arc melting followed of high temperature homogenization annealing [2]. Magnetic entropy change has been determined from magnetization isotherms up to a maximum magnetic field of 20 kOe applied parallel to the ribbon length (i.e. rolling direction). The second order nature of the magnetic transition of austenite was confirmed by the Arrott plots method. The material shows a maximum magnetic entropy change of ΔSMmax=-1.6 Jkg-1K-1, a refrigerant capacity of RC=80 Jkg-1 and useful working temperature range of 45 K(δTFMHW). A short-time vacuum annealing (10 minutes at 1073 K) led to an improvement in these magnetocaloric parameters (ΔSMmax=-2.4 Jkg-1K-1, and RC=100 Jkg-1). The RC value obtained together with other advantageous characteristics such as the cheaper material cost in comparison rare-earth based alloys as well as the fabrication via a single-step process, make austenitic Ni-Mn-In ribbons of potential interest as magnetic refrigerants for room temperature magnetic refrigeration.[1] J.L. Sánchez Llamazares, B. Hernando, C. García, J. González, Ll. Escoda, J.J. Suñol, J. Phys. D: Appl. Phys., 42 (2009) 045002.[2] T. Krenke, M. Acet, E.F. Wassermann, X. Moya, L. Mañosa, A. Planes, Phys. Rev. B 73 (2006) 174413.
G8: Magnetic Shape Memory Films
Session Chairs
Tuesday PM, December 01, 2009
Hampton (Sheraton)
4:30 PM - **G8.1
Structural, Magnetic and Phase Transformation Properties of Ternary Ferromagnetic Shape Memory Thin Films Based on Fe-Pd.
Alfred Ludwig 1 , Sven Hamann 1 , Sigurd Thienhaus 1 , Alan Savan 1 , Robert Meyer 1
1 Institute for Materials, Ruhr-University Bochum, Bochum Germany
Show AbstractFerromagnetic shape memory alloys (FSMA) are attractive for the realization of new sensors and actuators, due to their magnetic field induced strain (MFIS) effect. This work focuses on the development of new ternary Fe-Pd-X FSMAs with enhanced intrinsic properties: high martensitic transformation temperatures Ms> 90°C, high Curie temperatures Tc > 250°C, thermal hysteresis width < 10 K and high saturation magnetization µ0Ms > 1 T. Therefore Fe-Pd–X thin films (X= W, Mn, Pt, Cu) were fabricated in the form of composition spread materials libraries using combinatorial magnetron sputtering and investigated with high-throughput measurement methods. All thin films were annealed (850°C for 30 min) and quenched in order to obtain transforming phases. Furthermore, micro-hotplates were used for quenching studies of binary Fe-Pd thin films. The materials were investigated by energy dispersive X-ray spectroscopy, electrical resistance versus temperature measurements and temperature dependent X-ray diffraction. Additionally vibrating sample magnetometry and transmission electron microscopy was performed on selected samples. All presented Fe-Pd-X systems showed increased transformation temperatures and met the above defined requirements. In this talk the similarities and differences between the investigated systems will be presented. E.g., the Fe-Pd-W system was found to decompose by forming Fe67W33 precipitates embedded into a transforming Fe70Pd30 structure; whereas the other systems did not show precipitates or decomposition. The reasons for the increased transformation temperatures will be discussed with respect to compositional and stress effects.Acknowledgments: The financial support from the DFG (Heisenberg programme, SPP1239) is acknowledged.
5:00 PM - G8.2
Non-contact Strain Measurements based on Magnetic Shape Memory and Magnetostrictive Thin Films.
Christoph Bechtold 1 , Claas Thede 1 , Iulian Teliban 1 , Steffen Chemnitz 1 , Eckhard Quandt 1
1 , Inorganic Functional Materials, Christian-Albrechts-University Kiel, Kiel Germany
Show AbstractFor the detection of mechanical quantities such as strain or torque in sensor applications, inverse magnetostrictive materials are widely used. These materials offer in addition to a high sensitivity the possibility to measure a change in magnetic properties, e.g. permeability due to strain in a non-contact mode. However, measuring permeability is in most cases strongly dependent on the distance of the sensing pick-up coil to the magnetic material and is furthermore easily influenced by environmental disturbances (eg. temperature, humidity, etc.). To overcome these measurement difficulties, a more complex signal processing needs to be put in place. In this contribution such a system implementing frequency mixing and subsequent Fourier transformation is presented. A simulation of the measurement signal containing the amplitude at four distinct frequencies of the FFT shows good agreement with experimental data. Furthermore it is shown that the measurement technique is capable of a distance independent detection of the permeability.The measurement range of most inverse magnetostrictive materials is restricted to rather low strains, however amorphous metals showing inverse magnetostrictive behaviour up to a few percent strain can be used. The measurement range can be further increased by using magnetic shape memory thin films that reveal a theoretical strain of up to 6%. Strain measurements on freestanding polycrystalline FePd thin films fabricated by magnetron sputter deposition and the dependence of their magnetic properties on strain are presented and compared to the measurements of the amorphous metal.Funding and support via the DFG priority programmes SPP1239 and SPP1299 is thankfully acknowledged.
5:15 PM - G8.3
Freestanding Ni-Mn-Ga films: Uniaxial Texturation and Epitaxial Growth.
Jeremy Tillier 1 2 , Daniel Bourgault 1 , Nathalie Caillault 2 , Laurent Carbone 2
1 , CNRS/I. NEEL/CRETA, Grenoble Cedex 09 France, 2 , Schneider Electric, Grenoble France
Show AbstractFreestanding Ni-Mn-Ga films in the austenitic and the martensitic states at room temperature have been obtained using the DC magnetron sputtering technique. Two elaboration processes have been studied.A first batch of samples was deposited using a resist sacrificial layer in order to release the film from the substrate before vacuum annealing. This process leads to polycristalline films with a strong out-of-plane texture along the [022] direction. Structural and physical properties have been analysed using different characterisation techniques. The surface of a 5 micrometers thick film has been observed by optical microscopy during the martensitic transformation. Observations have been realized with in situ measurement of the resistivity temperature dependence. The in-plane magnetization loops have also been analysed during this first order magnetic phase transition. A second batch of samples was grown epitaxially on MgO(100) substrates using different deposition temperatures. The texture has been analysed with four-circle X-Ray diffraction. The epitaxial orientation in the austenite state to the substrate is Ni-Mn-Ga(001)[100]//MgO(100)[011]. Epitaxial freestanding films crystallised in the martensitic state at room temperature have also been obtained. The physical properties of this biaxially textured freestanding martensite have been analysed by vibrating sample magnetometry and resistivity measurements, applying the magnetic field in different directions. The long axis, being perpendicular to the film surface, has been found to be the hard magnetization axis.
5:30 PM - G8.4
Tunability of Crystal Structure and Magnetism in Highly Strained Epitaxial Films of the Fe70Pd30 Magnetic Shape Memory Alloy.
Joerg Buschbeck 1 , Ingo Opahle 1 2 , Manuel Richter 1 , Ulrich Roessler 1 , Peter Klaer 3 , Michael Kallmayer 3 , Hans-Joachim Elmers 3 , Gerhard Jakob 3 , Ludwig Schultz 1 , Sebastian Faehler 1
1 IMW, IFW Dresden, Dresden Germany, 2 Institut für Theoretische Physik, Universität Frankfurt, Frankfurt/Main Germany, 3 Institut für Physik, Johannes Gutenberg-Universität Mainz, Mainz Germany
Show AbstractIn the magnetic shape memory alloy Fe70Pd30 softening of the crystal lattice occurs in the vicinity of room temperature. For this material we demonstrate how the resulting structural instability of martensitic materials can be exploited for to stretch a metallic single crystalline film over an exceptional range. Strained Fe70Pd30 films are produced by coherent epitaxial growth on metallic buffer layers with different lattice constants using sputter deposition at room temperature. Large strains up to 7.3% are obtained, which result in a large variation of tetragonal distortion by 27%. The series of films with pseudomorphically distorted lattice structures covers most of the Bain transformation path from fcc to bcc structure. The mechanism for the exceptionally soft behaviour of the crystal structure along the Bain path is justified by density functional calculations. The calculations reveal a very flat energy landscape along the Bain path. In addition, the consequences of these changes in crystal structure on the anisotropic magnetic properties are investigated. The distortion of the lattice along the Bain path results in a significant change of the magnetocrystalline anisotropy constants K1 from about zero to 1.5*10^5 J/m^3 and K3 from about zero to 1.4*10^3 J/m^3. The strain dependence of the magnetic anisotropy is accompanied by a related variation of the orbital magnetic moment. This has been probed by XMCD measurements of the ratio between orbital and spin momenta of the Fe 3d electrons. Our findings demonstrate that functional properties like magnetic anisotropy can be tuned in pseudomorphically grown films with martensitic-like lattice instabilities. Since similar softening of the crystal lattice occurs in a variety of functional materials, our approach opens a viable route to the synthesis of film systems with tunable and improved physical properties.
G9: Poster Session: Magnetic Shape Memory Alloys
Session Chairs
Wednesday AM, December 02, 2009
Exhibit Hall D (Hynes)
9:00 PM - G9.1
Field and Temperature Dependence of Magnetization and Moesbauer Effect in Nanocrystalline fcc-Fe0.5Cu0.5 Invar Alloy.
Khalid Bouziane 1 , M. Elzain 1 , A. Yousif 1 , H. Lassri 2 , M. Abid 2 , O. Nemraoui 3
1 Physics, Sultan Qaboos University, Muscat Oman, 2 Laboratoire de Matériaux et de Microéléctronique, Université Hassan II, Casablanca Morocco, 3 Department of Physics and Engineering, University of Zululand, Kwadlangezwa South Africa
Show AbstractThe investigation of the temperature and field dependence of the magnetic properties of ball-milled equiatomic Fe0.5Cu0.5 alloy is reported. X-ray diffraction data in the temperature range 300-500K were analyzed by Reitveld refinement method showing that the system has a single fcc (γ) phase with an average grain size of 15 nm without any sign of crystallization or decomposition up to 400K. Slightly above 400K, the nanocrystalline alloy seems to undergo some atomic rearrangement most probably occurring at the grain boundaries with an evidence of the initiation of formation of α-Fe(Cu) phase as inferred from Mössbauer spectroscopy study. The coefficient of thermal expansion is found to be 7×10–6 K–1, typical of Invar effect. A splitting between zero field cooling (ZFC) and field cooling (FC) magnetization curves was observed below 400K but suppressed for fields above H = 5 kOe. Furthermore, a change in the sign at H = 1 kOe of the slope dMZFC/dT versus H is observed. A broad maximum of MZFC(T) centered at T = 220K for H = 1 kOe is observed. This result indicates that some spin freezing of domain orientation is taking place as the temperature decreases. The isotherms M(H) recorded at different temperatures were well described in terms of the random-anisotropy model (RAM) while the thermomagnetization M(T) at H = 13.5 kOe was found to obey Bloch’s law. The deduced spin wave stiffness constant D = 69.6 meV.Å2 and the exchange constant A(T) = 23×10–8 erg/cm at 77 K are about one order of magnitude smaller than that of pure α-Fe. The RAM analysis gives an average exchange field Hex = 4.5±0.5 kOe delimiting the two field dependence regimes. The random local anisotropy constant KL shows strong temperature dependence, being about 1.3×106 erg/cm3 at room temperature and increasing up to 2.3×106 erg/cm3 at 77K but overall larger than that of elemental α-Fe. The ferromagnetic correlation length was deduced as Rf =19±1nm similar to the grain size indicating a rather short-range interaction. This spin disorder or randomness as reflected by the RAM description of the isotherms and compositional disorder as inferred from Mössbauer results were analyzed using ab-initio calculations by considering different Fe environments and spin orientation configurations. Ferromagnetic and partial antiferromagnetic orderings with some particular environment of Fe were needed to explain the Mössbauer and magnetic data. Overall the magnetic features of the nanocrystalline γ-Fe0.5Cu0.5 Invar alloy correspond to a ferromagnet with week random anisotropy and may be ascribed to a correlated spin-glass state.
9:00 PM - G9.10
Domain Mechanisms in Magnetic Shape Memory Alloys: Phase Field Modeling and Simulations.
Yongmei Jin 1
1 Materials Science and Engineering, Michigan Technological University, Houghton, Michigan, United States
Show AbstractDomain mechanisms for coupled magnetization and deformation processes in magnetic shape memory alloys are investigated by phase field micromagnetic microelastic modeling. The computer simulations show the details of coupled magnetic and elastic domain evolutions and reveal the effects of various factors that significantly influence the evolution kinetic pathways, including external magnetic field strength and direction, internal domain configurations, and domain boundary mobility. It is found that the long-range magnetostatic and elastic interactions lead to complex domain processes, and produce peculiar magnetomechanical behaviors in magnetic shape memory alloys.
9:00 PM - G9.11
Magnetostrictive Performance of a 〈110 Oriented Crystal Tb0.3Dy0.7Fe1.95 After Magnetic Annealing.
Tianyu Ma 1 , Mi Yan 1
1 Department of Materials Science and Engineering, Zhejiang University, Hangzhou China
Show AbstractTerfenol-D has attracted considerable interest due to its high magnetostrictive performance and low magnetocrystalline anisotropy at room temperature. The practical application of Terfenol-D always requires a large magnetostriction in a modest external field. Terfenol-D materials with <110> or <112> preferred crystal orientation are known to exhibit improved magnetostrictive performance when the initial demagnetization state is changed under the application of a uniaxial compressive pre-stress, which is usually called a magnetostriction “jump” effect. In this work, A <110> oriented rod of the alloy Tb0.3Dy0.7Fe1.95 was subjected to a magnetic heat treatment, cooling through its Curie temperature under 240 kA/m. Besides the improved magnetostriction under free conditions, the magnetically annealed rod still exhibited an obvious magnetostriction “jump” effect when subjected to a uniaxial compressive pre-stress. A giant magnetostriction of 2683×10-6 was achieved under 0.8T and 30 MPa, which became 60% larger than before magnetic annealing. Magnetic force microscopy (MFM) images present direct evidence to show the favor of magnetic domain configurations, which was contributed to the enhanced magnetostrictive performance.
9:00 PM - G9.12
Study of γ-Mn-Fe as Magnetostrictive Alloys.
Tianyu Ma 1 , JIngjing Zhang 1 , Aina He 1 , Mi Yan 1
1 Department of Materials Science and Engineering, Zhejiang University, Hangzhou China
Show AbstractGreat efforts have been taken on magnetostrictive materials to improve the field-induced-strain value as well as to reduce the material cost for applications in actuators, sensors, and transducers in recent decades. The well-known rare-earth iron intermetallic compounds Terfenol have attracted much attention due to their giant magnetostriction and low magnetocrystalline anisotropy, but their brittleness limits their applications [1]. The newly developed Fe-Ga alloys are regarded as potential candidates because of their high strength, good ductility and low saturation magnetostriction field [2]. Unfortunately, the cost of Ga element is high. More recently, it is found that an antiferromagnetic Mn42Fe58 alloy can possess a high magnetostriction of 169×10-6. This strain value is comparable to that of textured Fe-Ga alloys, but the field requested is two orders of magnitude higher than that needed for Terfenol or Fe-Ga alloys [3]. It is of interest to develop Mn-Fe alloy as a new kind of low-cost and ductile magnetostrictive material, and explore ways to reduce the magnetic fields required.This work investigates the influences of alloy composition, thermal treatment, and plastic deformation on the magnetostrictive performance of antiferromagnetic γ-Mn-Fe alloys. The results show that when x≤0.40, MnxFe1-x (0.30 < x < 0.55) alloys consisting of face-centered cubic (fcc) γ and hexagonal close-packed (hcp) ε phases possess poorer magnetostrictive property than the alloys with single γ phase when x > 0.40. The magnetostrictive performance of a fcc Mn0.42Fe0.58 alloy deteriorates after isothermal heat treatment at 1373K for 24 h due to the separation of the single γ phase into a mixture of γ, ε, and body-centered cubic (bcc) α phases. It demonstrates that a single γ phase in Mn–Fe alloys is essential for high magnetostriction. Through cold-rolling and subsequent annealing, magnetostrictive performance of a γ Mn0.5Fe0.5 alloy can be significantly improved. The single face-centered cubic γ phase is retained during deformation and recrystallization. Mixed textures of {011} <110>, {001} <110> and a weak {011} <100> component are observed in the as-rolled sheet, and are retained after annealing at 873K for 1 h. The preferred <110> orientation along the direction parallel to rolling is believed to be responsible for the improvement in magnetostriction. Our results suggest that γ-Mn-Fe can be a potential candidate in magnetostrictive applications.References[1] D.C. Jiles, Acta Mater. 51 (2003) 5907.[2] S. Guruswamy, N. Srisukhumbowornchai, A.E. Clark, J.B. Restorff, M. Wun-Fogle, Scripta Mater. 43 (2000) 239.[3] W.Y. Peng, J.H. Zhang, Appl. Phys. Lett. 89 (2006) 262501.
9:00 PM - G9.2
Heat Treatment Under Load of Polycrystalline Ni50Mn29Ga21 Alloy.
Claudia Huerrich 1 , Martin Poetschke 1 , Stefan Roth 1 , Bernd Rellinghaus 1 , Ludwig Schultz 1
1 Institute for Metallic Materials, IFW Dresden, Dresden Germany
Show AbstractThe alloy Ni-Mn-Ga arose great interest for its application as a magnetic shape memory material. This effect is caused by reorientation of twin variants by an external magnetic field. So far most of the experiments were concentrated on single crystals. But, this effect can also be realised in polycrystals which can be prepared much more efficiently. Here, polycrystalline samples were prepared by directional solidification with a <100> fibre texture of the high temperature cubic phase parallel to the heat flow. Afterwards a heat treatment was applied for chemical homogenization and stress relaxation in the austenitic state. Then the samples were heated up to the austenitic state and cooled down under load. The microstructure was analysed by Electron Back Scatter Diffraction (EBSD) before and after that treatment. Mechanical training in three directions was tracked by recording stress-strain curves. With increasing the number of training cycles the strain also increases.This work is supported by DFG within SPP 1239.
9:00 PM - G9.3
Thermal Annealing Influence on Magnetic and Structural Properties of Cu56Ga28Mn16 Microwires.
Victor Prida 1 , Victor Vega 1 , Jose Sanchez-Llamazares 1 , Maria Sanchez 1 , Blanca Hernando 1 , Joan Sunol 2 , Lluisa Escoda 2 , Carlos Garcia 3 , Caroline Ross 3
1 Física, Universidad de Oviedo, Oviedo, Asturias, Spain, 2 , Universidad de Girona, Girona, Cataluña, Spain, 3 Materials Science and Engineering, MIT, Cambridge, Massachusetts, United States
Show AbstractFerromagnetic glass-coated microwires based on Cu-Ga-Mn alloy have recently awoken an increasing scientific interest due to their high ductility and potential applications as ferromagnetic shape memory alloys related to the martensitic phase transformation exhibited by these materials, together with their promising features as magnetocaloric materials [1-3]. Here we report on the crystalline structure, morphology and magnetic properties of glass-coated magnetic microwires with Cu56Ga28Mn16 sample composition, as well as the thermal annealing influence on its magneto-structural properties. Cu-Ga-Mn glass coated microwires having an inner metallic nucleus diameter around 17 μm and glass-coating outer shell diameter about 26 μm, were produced by the Taylor-Ulitovsky method [1, 4]. Thermal annealing treatments of the microwires were performed in an open to air furnace at different temperatures ranging between 473 and 873K in order to evaluate its effect on both, the crystalline structure and magnetic properties of the samples. X-ray diffraction, Scanning Electron Microscopy (SEM) with Energy Dispersive Spectroscopy microanalysis (EDS) and thermomagnetic measurements in a PPMS platform with VSM module in the temperature range from 350 K down to 50 K and applied magnetic field values of 200 Oe and 50 kOe, were employed for studying the evolution of microstructure and magnetic properties of the alloy as a function of the annealing temperature. The main phase formed in as-cast CuMnGa microwires exhibits a cubic B2 crystalline structure with a lattice parameter a = 0.2939(6) nm. Moreover, a fcc Cu-rich minority phase with a = 0.3592(5) nm, together with the monoclinic CuO on the sample surface were detected [4]. Upon annealing at temperatures up to 573 K, (where the sample composition maintains its homogeneity), the samples' microstructure evolve at annealing temperatures above 373 K, where a new hexagonal phase appears coexisting with the cubic B2 major phase. Thermal annealing at higher temperatures (673-873 K) showed a similar structure with varying lattice parameters of the hexagonal phase and a migration of Mn atoms from the nucleus to the metallic surface of the microwires. ZFC-FC thermomagnetic curves at 200 Oe of the microwires in the as-cast state show a clear coexistence of two ferromagnetic phases with a Curie temperature of around 125 K for the major phase, while the samples annealed at temperatures over 573 K eshibits nearly vanishing of ferromagnetic phase. However, the FC curve of sample annealed at 498 K exhibits a magnetization decreasing below 150 K, indicating the coexistence of some antiferromagnetic and ferromagnetic interactions due to Mn-Mn atomic positions.[1] A. Zukov, Adv. Funct. Mater. 16 (2006) 267.[2] K. Oikawa et al, Mater. Transactions 45 (2004) 2780.[3] M. I. Ilyn et al, phys. stat. solidi (a) 205 (2008) 1378.[4] C. García et al, phys. stat. solidi (a) 206 (2009) 644.
9:00 PM - G9.4
Thickness Dependence of Structure, Micro Structure and Morphology in Epitaxial Ni-Mn-Ga Films.
Anja Backen 1 , Stephen Doyle 2 , Manfred Kohl 3 , Ludwig Schultz 1 , Sebastian Faehler 1
1 , IFW Dresden, Dresden Germany, 2 , Forschungszentrum Karlsruhe, Eggenstein-Leopoldshafen Germany, 3 , University of Karlsruhe, Karlsruhe Germany
Show AbstractThe magnetic shape memory (MSM) alloy Ni-Mn-Ga provides a broad application spectrum since high strains can be achieved by reorientation of martensitic variants when applying a magnetic field. The integration of Ni-Mn-Ga as smart material in Microsystems requires the production of thin films or foils. The deposition of epitaxial films is most suitable for this kind of application since the highest strains of up to 10 % have only been observed in bulk single crystals. Our previous studies [1,2] have been focused on temperature dependent properties such as structure, composition and magnetic behaviour of thin films with constant thicknesses of 500 nm. In contrast to those studies we report on the thickness dependence of the properties mentioned above. How does the film thickness affect the structure and morphology of the martensitic films? By decreasing the film thickness to a few nanometres, the interface between the substrate and the film should have an increasing influence on the properties of the Ni-Mn-Ga films. Furthermore the twin size as well as the domain size are commonly expected to depend on the film thickness d and scale with √d. It was recently predicted, that in case of very thin films, the variant size should increase again [3]. In order to get an answer to those questions, we deposited thin epitaxial Ni-Mn-Ga films on single crystal MgO(100) substrates using DC-sputter deposition from a non-stoichoimetric target Ni46Mn32Ga22. During the deposition the temperature was kept at a constant and optimized value of 400°C while the film thickness was varied from 1µm down to 5 nm. The structure of selected films was examined using X-ray diffraction at the synchrotron radiation source in Karlsruhe, Germany (ANKA). Furthermore the morphology of the films was investigated using Atomic Force Microscopy (AFM). The dependence of the twin size and twin periodicity on the film thickness is shown. [1]M. Thomas et al.: Magnetically induced reorientation of martensite variants in constrained epitaxial Ni-Mn-Ga films grown on MgO(001). New Journal of Physics 10 (2008) 023040[2]J. Buschbeck et al.: In situ studies of the martensitic transformation in epitaxial Ni-Mn-Ga filmsActa Materialia 57 (2009) 2516-2526[3]N.S. Kiselev et al.: .Theory of stripe domains in magnetic shape memory alloys. European Physical Journal-Special Topics 158 (2008) 119-124
9:00 PM - G9.5
Structural Characterization of PLD-grown Nanometer Size Ferromagnetic NiFeMo Films.
Mitali Banerjee 1 , Alak Majumdar 1 , Ram Choudhary 2 , D. Phase 2 , Sanjay Rai 3 , Pragya Tiwari 3 , G. Lodha 3
1 Materials Science, S N Bose National Centre for Basic Sciences, Kolkata 700098 India, 2 , UGC-DAE Consortium for Scientific Research, Indore 452017 India, 3 , UGC-DAE Raja Ramanna Centre for Advanced Technology, Indore 452013 India
Show Abstract Thin films of 3 different thickness each of Ni83.2Fe3.3Mo13.5 and Ni83.1Fe6.0Mo10.9 alloys have been grown using Pulsed Laser Deposition (PLD) technique. Our motivation is to investigate the magnetic properties of a few nm thick Ni alloys with mostly Mo (4d element) addition since the corresponding soft ferromagnetic bulk alloys have shown very small coercivity of ~ 0.1 Oe. Detailed structural characterization has been undertaken before probing the magnetic properties. Arc melted alloy buttons after homogenization are used directly as targets for the deposition. Films were deposited on single crystal Sapphire (0001) substrates using excimer laser. The structural characterization has been done by X-ray diffraction (XRD), X-ray reflectivity (XRR), Energy dispersive x-ray spectroscopy (EDS), and Atomic force microscopy (AFM). The X-ray diffraction pattern shows that the films are highly textured and grown along [111] direction of the alloys. They have high lattice strain which makes the films highly resistive and the resistance decreases with increasing thickness. The EDS measurements, using Scanning electron microscope (SEM), indicate that the compositions of the films are almost the same as those of the targets. Thickness, roughness, and density gradients are estimated using XRR measurements. The thinner films have higher roughness compared to the thicker ones for both the compositions. The films have density gradient across their thickness. The bottommost low density layer has high roughness which is supposed to be the result of initial non uniform coverage of the substrate. The density of the middle layer, having the lowest roughness, is approximately near the bulk value and it increases with increasing film thickness. The change in density is not due to the variation of composition; instead it is due to the variation of void densities in the layers. The topmost layer, having the lowest density and the highest roughness, is interpreted as a porous layer which is also evident from the AFM images. Detailed magnetic characterization of these thin films is in progress. Interestingly, the preliminary data suggest that their coercive field, initial permeability, and Curie temperature are larger than those of the bulk targets.We acknowledge Drs. V. Ganesan and A. Banerjee for their cooperation and guidance. M.B and A.K.M acknowledge UGC and DST for funding.1
[email protected], 2
[email protected] (Corresponding author)
9:00 PM - G9.6
Study of Magnetic Properties of Ni-Mn-X (X = Ga, In, Sn, Sb) Heusler Alloys by Monte Carlo Technique.
Vasiliy Buchelnikov 1 , Vladimir Sokolovskiy 1 , Sergey Taskaev 1 , Peter Entel 2
1 , Chelyabinsk State University, Chelyabinsk Russian Federation, 2 , University of Duisburg-Essen, Duisburg Germany
Show AbstractToday a large number of laboratories and universities in Europe, South and North USA, Canada, China and Russia carry out the intensive theoretical and experimental works devoted to search optimal refrigerants used in a magnetic cooling technology. The magnetic cooling based on a possibility any magnetic materials to change its temperature (ΔT > 0 or ΔT < 0) after applying an external magnetic field. This effect is called the magnetocaloric effect (MCE).Recent experimental studies have shown that Heusler Ni-Mn-X (X=Ga, In, Sn, Sb) alloys are also the perspective materials by way of refrigerants in cooling devices. The gigantic MCE observed in these compounds has same values as well as in some other ferromagnets, e.g. Gd-Ge-Si, Mn-As, La-Fe-Si etc. Moreover these alloys more cheaper, non-toxically, environmental friendly and they have unique properties such as the shape memory effect, the large magnetostriction, the large magnetoresistence and other magnetic properties. In this work we present the theoretical investigation of phase transitions and the MCE of the Ni-Mn-X (X=Ga, In, Sn, Sb) alloys undergoing first order magnetostructural and metamagnetostructural phase transitions by a classical Monte Carlo technique [1]. Theoretical study has been carried out at two types of three-dimensional model lattice. For the first type of it we have used the simple cubic lattice with Mn and Ni atoms that are randomly set on it. Since the magnetic moment of Ni and X atoms is less then one of Mn atoms we have neglected the contributions from the Ni and X atoms and considered only the interactions between the magnetic Mn atoms. For the second type of model lattice we have taken the cubic lattice with real unit cell of the Heusler alloys with Ni, Mn and X atoms. Since the ab initio calculations of magnetic exchange constants between Mn, Ni and X atoms have shown that the Mn-Ni interaction played an important role in a formation of ferromagnetism in Heusler alloys [1], so in our work we have taken into account interactions between all atoms and the values of magnetic integrals was taken from ab initio calculations for Ni-Mn-X alloys. In both cases whole system can be represented as by two interacting magnetic and structural contributions. For the magnetic part we have chosen q state Potts model and Heisenberg model which allow to simulate the magnetic phase transition [1]. The structural part is described by the three-state Blume-Emery-Griffiths model allowing for a structural phase transformation from the austenitic phase to the martensitic one [1].By the help of theoretical model the temperature dependences of the magnetization, heat capacity, positive and negative MCE for Ni-Mn-X alloys are obtained. It is shown that theoretical results are in good qualitatively agreement with the available experimental one.[1] Buchelnikov V et al. Phys.Rev. B 78 (2008) 184427.
9:00 PM - G9.7
Magnetic Correlations in Ni-Mn Based Ferromagnetic Shape Memory Alloys Studied by Neutron Polarization Analysis.
Seda Aksoy 1 , Mehmet Acet 1 , Pascal Deen 2 , Lluis Manosa 3 , Antoni Planes 3 , Eberhard F. Wassermann 1
1 Experimental Physics, Duisburg-Essen University, Duisburg Germany, 2 , Institut Laue-Langevin, Grenoble France, 3 Departament d'Estructura i constituents de la Matèria, Universitat de Barcelona, Barcelona Spain
Show AbstractNi-Mn-Z (Z=In, Sn and Sb) based Heusler alloys exhibit martensitic transformations, whereby the magnetization decreases just below the martensite start temperature (Ms). The hydrostatic pressure plays a big role on transformation temperature which is shifted to higher temperatures (1). The temperature-dependent neutron polarization analysis shows that ferromagnetic correlations exist above Ms and antiferromagnetic correlations appear just below Ms (2). We have performed the neutron polarization analysis under hydrostatic pressure up to 10 kbar in off-stoichiometric Ni-Mn-Sb and Ni-Mn-In Heusler alloys to discuss the existence of antiferromagnetic exchange below Ms. (1) Manosa et al., Appl. Phys. Lett., 92 (012515) 2008.(2) Aksoy et al., Phys. Rev. B, 79 (212401) 2009.
9:00 PM - G9.8
Dispersion Both `Heat-Exchange' by Similarity Effect `Chemical Pressure' and `Heat Dissipative.'
Ahmad Yazdani 1 2 , Baozhi Cui 2 , Wanfeng Li 2
1 Department of Basic Science, Tarbiat Modares University, Tehran Iran (the Islamic Republic of), 2 Department of Physics and Astronomy, University of Delaware, Newark, Delaware, United States
Show AbstractWhile Si+4 and Ge+4 belong to the same column of periodic table the magnetic state of the substituted Gd5(Si,Ge)4 compounds are different .The cause\source of effective parameter which has so much different influence on the conversion substitution is not well known. The reported phase impurity which may be related to the phase diagram is not much more clear. The aim of this paper is to study the response of the magnetic and crystal structure of Gd5Si4 to both ‘isothermal’ and ‘thermo mechanical’ processing to determine the effect of’’latent heat’ and ‘dissipative heat’ on the exchange fluctuation which is believed to be the cause of the Gd5Si4 meta-stability. The correspondence of the chemical pressure, (which is defined by the size effect of RGe+4>RSi+4 on the band width) with the dissipative heat (which is define by the thermo mechanical process) is manifested by measurements of X-ray diffraction, DTA and VSM at room temperature. It is evidente that, the magnetization of the high energy ball milled Gd5Si4 is similar to the magnetization of the annealed Gd5Si2Ge2 . The XRD patterns show individual peaks in three distinct groups to merge to each other and collapse to three broadened regions averaging to each group of intensities line of annealed sample .The correspondence between the three regions of X-ray patterns can be reflected by the entangle of the strong fluctuation of atomic position, due to the high heat exchange energy dissipative by the high energy ball milled process which can be the cause of cluster formation in the sample. The cluster formation which is reflected on the SEM may be intrinsic and characteristic of the three group of Gd nearest neighbor. The cluster formation is the result of topological atomic position of disordering due to strong distortion of the unit cell. The created distortion energy can deform the unit cell lowering the free energy of the crystal while increasing the exchange fluctuation. This can be considered as a kind of topological distortion which depends on the energy of band modulation and in some part on the exchange which is due to the lack of hybridization. The distortion can change the sign and the strength of the phase transition and also the spin atomic site dispersion, which is associated with both the magnetic and crystal structure of the affected Gd4Si4 similar to that of Gd5Si2Ge2 .However, it could be concluded that the similarity of magnetic structure of high energy milled Gd5Si4 with the annealed Gd5Si2Ge2 could be due to the loss the long –range crystalline orientation. This is the cause of cluster formation due to the short –range magnetic order of the exchange coupled of nearest neighbor magnetic ions.
9:00 PM - G9.9
Development of an Air-Gap Free Disk Spring/MSMA Actuator Assisted by a Conventional Voice Coil.
Jan Guldbakke 1 , Arno Mecklenburg 2 , Rainer Schneider 3 , Annika Raatz 1
1 Institute of Machine Tools and Production Technology, TU Braunschweig, Braunschweig Germany, 2 , MSM Krystall GbR, Berlin Germany, 3 , Helmholtz-Centre Berlin for Materials and Energy, Berlin Germany
Show AbstractIn the field of micromechanics smart materials are actively used. They offer a high resolution and distributed actuation. A barely new smart material is the class of Magnetic Shape Memory Alloys (MSMA). The alloys offer a large strain (about 10%) like conventional thermal shape memory alloys (SMA), but can provide a 100 times shorter response time. The main disadvantages of the MSM alloys are the brittleness of the single-crystals, strong magnetic field which has to be applied to overcome the twinning stress and to generate a sufficient strain. Furthermore common magnetic shape memory crystals can only provide small blocking stresses of 2-3 MPa which are smaller than these of SMAs (150-200 MPa). The here presented actuation concept has the advantage that the twinning stress is compensated and much higher output forces can be achieved. The disk spring/MSMA actuator can be divided in two parts. The first part consists of a conventional voice coil and the second part of a MSMA element and a magnetic circuit. Both parts are connected over a nonlinear disk spring combination. Furthermore the MSM element is preloaded with a second spring disk spring combination perpendicular to voice coil-MSMA element. With the voice coil a mechanical pulse can be generated which compresses the disk spring system. This mechanical pulse is then used to overcome the blocking stress as well as the preload of the MSM element and provide work. As soon as the blocking stress is overcome, the inductance of the magnetic circuit changes. This change of inductance is detected and the magnetic circuit is energized. If the compression of the MSMA element is finished, the second disc spring combination carried the crystal back into its initial state. The function of the MSM element in the actuator can be described as a transmission which additionally generates work by means of the MSM effect. The work output is therefore the sum of the work that is generated by the Voice Coil/Disk Spring system (minus the work required to compensate the blocking stress) and the work which is provided by the MSM element.As an actuation element a 5M-Ni-Mn-Ga single crystal is used. The MSM crystal was produced at the Helmholtz Centrum Berlin and has a size of 2x10x 10mm3. The integrated MSM alloy exhibits a stress induced strain of approximately 5 % and can be activated with magnetic fields less than 1 T. For the layout of the coil system to generate the required magnetic field the finite element program ANSYS was used. The transmission ratio of MSM element is 1:5 and an overall displacement of 0.6 mm can be achieved by the actuator.
Symposium Organizers
Eckhard Quandt University Kiel
Manfred Wuttig University of Maryland
Tomoyuki Kakeshita Osaka University
Sebastian Faehler IFW Dresden
G10: Galfenol: From Fundamentals to Applications
Session Chairs
Wednesday AM, December 02, 2009
Hampton (Sheraton)
9:30 AM - **G10.1
Unraveling the Magnetostriction in Galfenol: Neutron Scattering Explorations.
Mark Laver 1 2 3 , Chaitanya Mudivarthi 1 , James Cullen 1 , Alison Flatau 4 1 , Wangchun Chen 3 , Shannon Watson 3 , Manfred Wuttig 1
1 Materials Science and Engineering, University of Maryland, College Park, Maryland, United States, 2 Laboratory for Neutron Scattering, Paul Scherrer Institut, Villigen Switzerland, 3 , NIST Center for Neutron Research, Gaithersburg, Maryland, United States, 4 Aerospace Engineering, University of Maryland, College Park, Maryland, United States
Show AbstractMany materials exhibit magnetostriction but in the iron-gallium alloys (Galfenol) the effect can be exceptional. The magnetostrictive behavior of bulk Galfenol is well-characterized, but the microscopic properties and origin of the large magnetostriction have attracted much controversy and debate [1,2]. Here we report on exciting neutron scattering measurements which reveal nanoscale heterogeneities whose average magnetic moment is quite distinct from the bulk. Further, our sample’s magnetostriction is observed to be intimately related to the reorientation of the moments within and in the neighborhood of these nanostructures.
While pure bcc iron experiences changes in shape of ~20 ppm with saturating magnetic fields, single-crystal FeGa alloy (Galfenol) can exhibit saturation magnetostriction in excess of 250 ppm for quenched samples. In conjunction with low hysteresis, favorable material costs and ductile properties, magnetostrictive Galfenol offers auspicious and prominent applications in transducers and micro-actuators.Although considerable effort has been undertaken successfully to improve the magnetostriction of this class of alloys, our understanding of the underlying mechanism is far from complete. Here we first focus on a 19 at.% Ga sample that was quenched from high preparation temperatures and irradiated with electrons, with aim to proliferating D022 inhomogeneities that have been suggested by one of the competing theories to effect to large magnetostriction [2].Using small-angle neutron scattering to probe directly the nanoscale landscape within this single-crystal, we first uncover heterogeneities with an average spacing of ~15 nm. By analysis of the neutron polarization, we find these heterogeneities are magnetically distinct from the matrix. Portentously, their magnetization vector is observed to rotate not only with applied field, but also with applied uniaxial compressive stress.
We subsequently present further results from neutron scattering explorations across a range of samples differing in Ga contents and preparation schemes. The general significance of the observed heterogeneities to the extraordinary magnetostriction exhibited by the macroscopic material is discussed.
[1] J. Cullen, P. Zhao, M. Wuttig, J. Appl. Phys. 101, 123922 (2007).[2] A. G. Khachaturyan, D. Viehland, Metall. Mater. Trans. A 38A, 2317 (2007).
10:00 AM - **G10.2
Magnetic Domain Imaging in FeGa.
Chaitanya Mudivarthi 2 , Mark Laver 2 , James Cullen 2 , Manfred Wuttig 2 , Alison Flatau 1 2
2 Material Science & Engineering, University of Maryland, College Park, Maryland, United States, 1 Aerospace Engineering, University of Maryland, College Park, Maryland, United States
Show AbstractIn ferromagnetic materials with negligible magnetostriction the magnetic domain structure is dictated by the balance of crystalline anisotropy, exchange, magnetostatic, and Zeeman energies. In addition to these energies, the domain structure of magnetostrictive ferromagnetic materials is dictated by the magnetoelastic energy – meaning the domain structure depends not only on the applied magnetic fields but also on the elastic fields. Therefore, magnetostrictive materials both deform and change their magnetization in response to external magnetic and elastic fields. These properties of magnetostrictive materials can be used for sensing and actuation purposes.Recent discovery of large magnetostriction (lambda-sat ~400 ppm) in Fe100-xGax alloys [1] is attracting much attention due to their ductile-like behavior with higher tensile strengths (~400 MPa) compared to other magnetostrictive materials. In conjunction with their large magnetostriction, machinability, and low saturation fields, they offer immense potential as robust transduction materials. The magnetostriction in these alloys monotonically increases from 36 ppm to ~400 ppm at x=20 with the addition of Ga. Measurements of anisotropy constants K1 and K2 showed a gradual decrease of the magnitude of these constants with the addition of Ga, both changing signs at x = 20 [2]. It was also observed that the [100] crystalline direction was the easy axis for x < 20 while [100], [110] and [111] crystalline directions were equally easy or hard for x = 20 [2].It is expected that the domain structure of FeGa is hugely dependent on the elastic fields because of its large magnetostriction. In this work, we studied magnetic domains in Fe100-xGax for x = 17,18, and 19 in real-time using magneto-optic Kerr effect microscope. An in-situ stress application device was built so as to image the domains while applying simultaneous magnetic and elastic fields. The intensity of the images at low magnifications was used to estimate the magnetic state of the sample while a strain gage was used to measure its elastic state. The estimates of the magnetoelastic energy from the domain structure change were compared with those obtained from the bulk measurements in literature.References[1]A. E. Clark et al., Magnetics, IEEE Transactions on, 36, 3238-40, 2000.[2]S. Rafique et. al., Journal of Applied Physics, Vol. 95, Issue 11, 2004
11:00 AM - G10.3
Decomposition and Ordering in the Fe-Ga bcc Alloys: Atomic Phase Field Modeling and Diffuse Scattering Study.
Julien Boisse 1 , Armen Khachaturyan 1
1 Materials Science, Malcolm G. McLaren Center for Ceramic Research (MGMCCR) , Piscataway, New Jersey, United States
Show AbstractThe Fe-Ga bcc alloys within the 15-20 at% Ga composition range have abnormally high magnetostriction. There is growing evidence that this effect is associated with the formation of a dispersion of nanoscale DO3 ordered particles, which undergo cubic-->tetragonal displacive transformation transforming these particles into three orientation domains of the tetragonal phase. Large magnetomechanic effect is caused by The reorientation of these domains under the magnetic field. In this study we investigated the structural, ordering and clustering processes within this composition range by using the computer modeling in the Atomic Density Field approximation. The first, second and third atomic interaction model was used. The parameters of this model were fitted to the known solubility limits of the bcc and DO3 ordered phases. The computer modeling of the equilibration of the compositionally homogeneous bcc solid solution resulted in a heterogeneous microstructure consisting of DO3 ordered nanoparticles. The geometry of this nanostructure is in excellent agreement with that observed in the HREM images. Using the kinematic theory of the x-ray scattering and the microscopic crystal lattice statics, we calculated diffraction patterns of the diffuse scattering generated by such a nanostructural state for the cases wherein the nanoparticles have the DO3 atomic structure obtained in the modeling and the case wherein the nanoparticles undergo the cubic--> tetragonal confined martensitic transformation. These cases were compared with the experimental observations.
11:15 AM - G10.4
Short Range Ordering of Fe-Ge and Fe-Ga Single Crystals.
Mianliang Huang 1 , Tom Lograsso 1
1 Institute for Physical Research and Technology, Iowa State University, Ames, Iowa, United States
Show AbstractThis study reports on the short range ordering (SRO) in Fe-18.4 at.% Ga and Fe-9 at.% Ge alloys. Short range ordering was measured by x-ray θ-2θ scans on slow cooled (100) and (111) single crystalline specimens. Single crystalline samples were used to maximize diffracted intensities of the weak, diffuse scattering exhibited by these alloys. A diffuse (100) peak was observed in (100) crystals for both Fe-Ga and Fe-Ge alloys. However, a diffuse scattering peak at the (½, ½, ½) reflection was observed (from the (111) crystal) only for the Fe-Ga alloy, consistent with previous studies that the short range ordering of the Ga atoms in Fe-Ga assume has D03 chemical ordering tendencies. In contrast the absence of a diffuse scattering peak at the (½, ½, ½) in Fe-Ge rules out D03 character and only B2 chemical ordering tendencies are found for the Ge atoms in Fe-Ge alloys. The correlation length of the B2 and D03 SRO clusters is ~ 3.6 and 4.3 nm for Fe-9 at.% Ge and Fe-18.4 at.% Ga alloys, respectively. The B2 short range ordering found in Fe-Ge is not necessarily consistent with the mechanism of enhanced magnetoelasticity proposed by Khachaturyan and Viehland [A. G. Khachaturyan and D. Viehland, Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science 38A, 2308-2316 (2007)] which relies on the D03 -D022 displacive transformation that leads to magnetically active tetragonally distorted nanoclusters, suggesting an alternative mechanism is responsible for the increases in magnetostriction in Fe-Ge alloys.
11:30 AM - G10.5
Influence of Quench Rate on Magnetostriction in Iron-Gallium Alloys.
Qingfeng Xing 1 , Thomas Lograsso 1
1 Division of Materials Sciences and Engineering, Ames Laboratory, Ames, Iowa, United States
Show AbstractThe discovery of Fe-Ga alloys in 2000 opens a totally novel design paradigm for the devices utilizing magnetostrictive materials, mainly because the alloys are robust and machinable, and can operate under applied tensile stress at full magnetostriction (MS). Recently, we have experimentally clarified the phase dependence of the magnetostrictive behavior [Xing et al, Acta Mater 56 (2008) 4536–4546]. There are four magnetostriction-composition regimes. In regime I of disordered single phase A2 and regime III of well ordered single phase D03, the tetragonal MS, (3/2) λ100, increases with Ga content. In both regimes II and IV where two-phase mixtures of A2 + D03 and D03 + secondary phases respectively are found, the degree of second phase is known to be thermal history dependent. The D03 phase and secondary phases in small size do not influence the distribution of the magnetic domains in the alloys, unless the secondary phases at higher Ga content are pronounced and large in size. A corresponding variation of the rhombohedral MS (3/2) λ111 is also found over the same concentration range. In order to investigate whether higher MS can be obtained in single phase A2 phase field, we examined the influence of quench rate on retaining single phase near the phase boundary. The sample disks were made from Bridgman-grown single crystals, and were thermally processed in several ways, followed by the MS measurements after each thermal processing. The thermal processes are: cooling from 1000 °C at a well-controlled rate of 600 °C min-1 (slow cooling), quenching into ice-water from 1000 °C (ice-water quench), quenching into a Ga-In-Sn liquid metal at room temperature (metallic quench). Severe quench cracking in samples with high Ga contents limited the quench studies to Ga contents up to 21.4 at%. The MS was measured via a standard strain gage method under 20 kOe.Significant improvements in MS over slow-cooled samples was found as a result of quenching only for compositions > ~17 at% Ga. Between ~17 at% Ga and ~20 at% Ga, the degree of quench rate (room-temperature water quench vs ice-water quench) shows little change in the MS for a given Ga content. However, the metallic quench improves the MS slightly for Fe-19.8 at% Ga and Fe-21.4 at% Ga while a significant change was observed for Fe-25.2 at% Ga. The first maximum in MS corresponding to the boundary between regimes I and II was push to 21.4 at% Ga with a MS of 420 ppm via the metallic quench. The previously reported maximum MS in binary Fe-Ga alloys for the first peak was 390 ppm from a room-temperature water quenched Fe-20.6 at% Ga. This dependence of the MS on cooling rate is associated with the suppression of Ga ordering process and is in good accord with our previous transmission synchrotron x-ray scattering and electron microscopy studies of this alloy system. Our previous studies clearly show that occurrence of long-range ordering decreases the MS and are consistent to the current data set.
11:45 AM - **G10.6
Galfenol-based Sensor/Actuator Devices for Smart by-Wire Steering System for Automobile Technology.
Yasubumi Furuya 1 , Chihiro Saito 2 , Teiko Okazaki 1 , Kazumi Okada 1 , Yusuke Sado 1 , Kakeo Chinen 1 , Naoki Ogasawara 1 , Muneaki Shimada 3
1 Intelligent Machines and System Engineering, Hirosaki University, Hirosaki Japan, 2 NJC Research Center, Namiki Precision Jewel Co.,Ltd , Tokyo Japan, 3 Technical Research Institute, NISSAN Motor Co.Ltd, Yokosuka Japan
Show AbstractPolycrystalline Galfenol (Fe-Ga-X, X=Al, C, Zr etc.) alloys were fabricated as a bulk sample from rapid-solidified powders or ark-melted and annealing process method for enhancing various engineering applicability. (Fe-Ga0.15-Al0.05)99.0-Zr0.5-C0.5 [at.%] sample showed a maximum magnetostriction of λmax=90ppm to 150ppm as well as a tensile stress over σ=800MPa. This large magnetostriction is caused by non-precipitating of the ordered A2 phases without the excessive precipitation of ordered phases such as fcc ordered L12 and bcc ordered D03 phases, the release of considerable large internal stresses in as-spun ribbon and the remained [100] oriented strong textures by a heat treatment. Based on the improvements of properties in strength, toughness, hardness, wear resistance in the developed bulk Galfenol alloys FeGaAlX. Secondarily, we will introduce an application as a smart torque sensor by utilizing Galfenol-ring around the steering shaft for steering-by-wire system of automobile. In this system, a torque sensing system by using the magnetostrictive ring of FeGa (Galfenol) alloy was developed and magnetic flux leakage from the Galfenol ring attached on the rotating shaft was experimentally measured by using two differential Hall probe sensor. As a result , the sensitivity in FeGaAl-C alloy increased by about six times at rotations speed 250rpm in comparison with SK-105, and an almost linear relationship between pick-up voltage and applied toque value was obtained. In conclusion, our developed Galfenol alloys will be applicable for a simple structured ring-type torque-sensor for near future steering-by-wire system in automobile technology.
12:15 PM - G10.7
Growth and Physical Properties of Magnetic Shape Memory Alloy Thin Films.
Tobias Edler 1 , Iris Kock 1 , Lisa Kuehnemund 1 , Guido Mahnke 1 , Stefan Mayr 2 3
1 I. Physikalisches Institut, Universität Göttingen, Göttingen Germany, 2 , Leibniz-Institut für Oberflächenmodifizierung e.V., Leipzig Germany, 3 Fakultät für Physik und Geowissenschaften und Translationszentrum für Regenerative Medizin, Universität Leipzig, Leipzig Germany
Show AbstractMiniaturization of magnetic shape memory alloys is an important issue for their application in micro actuation. To ensure adequate functionality a profound knowledge of the impact of reduced dimensionality, surfaces and substrate constraints, as well as the underlying physics are essential. To obtain a comprehensive overview of the impact of preparation conditions and to identify structure - property - correlations, NiMnGa and FePd samples prepared by sputtering, physical vapor deposition and ultra rapid quenching were characterized experimentally. NiMnGa films were optimized with respect to crystal structure and transition temperature. A microscopic model explaining the influence of substrate constraints on the distribution of martensite variants observed in TEM studies is presented. FePd films can be grown epitaxially on MgO substrates for thicknesses up to several hundred nanometers due to concurrent relaxation of misfit stresses. The stress relaxation mechanism and the influence of precipitates were compared with classical MD simulations on a model system and revealed agreement with high resolution TEM measurements.