Peter Fischer1,2
Lawrence Berkeley National Lab1,University of California, Santa Cruz2
Peter Fischer1,2
Lawrence Berkeley National Lab1,University of California, Santa Cruz2
Topologically protected magnetic structures, such as skyrmions, are currently an intensely studied topic in the nanomagnetism community due to their scientific beauty and deep fundamental insight into nanoscale spin systems, but also with regard to potential future applications towards low-power, high-density and high-speed information technologies, which are required for the Internet-of-Things (IoT) and beyond [1-3]. <br/>Skyrmions are two dimensional chiral solitons where the magnetization smoothly covers a solid angle density of radians coherently from the center of the spin texture to the opposite magnetization outside of the spin texture [4-5]. Recently, it has been realized, that expanding into the third dimension opens a door to explore highlycomplex topological magnetic structures that can only exist in 3D [6]. Among those 3D textures are magnetic Hopfions [7], which are three-dimensional knot-solitons with a topological class defined by its linking number. Theory has predicted that magnetic Hopfions can be stabilized, e.g., in chiral magnets. Those systems can host target skyrmions (TSks) which are seen as precursors to Hopfions [8-9].<br/>Our recent research was able to stabilize magnetic Hopfions in tailored magnetic multilayers with a depth varying perpendicular anisotropy, and we confirmed the static properties of those Hopfion textures by a combination of two advanced x-ray spectromicroscopy techniques, specifically surface sensitive X-PEEM and bulk sensitive MTXM which allowed us to delineate Hopfions from TSks and torons [10].<br/>In this presentation, we will discuss our recent experimental studies of the static character of magnetic Hopfions, using advanced X-ay microspectrosopy techniques, as well as results from micromagnetic simulations with high-performance computing (HPC), where we identified a field-driven transition from a Hopfion texture to a toron with distinct dynamics for each of the spin textures [11].<br/><i>This work was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Materials Sciences and Engineering Division Contract No. DE-AC02-05-CH1123 in the Non-Equilibrium Magnetic Materials Program (MSMAG).</i><br/>[1] A. Fert, N. Reyren and V. Cros, Nature Reviews Materials <b>2</b> (7), 17031 (2017).<br/>[2] S. Woo, K. Litzius, B. Krüger, M.-Y. Im, L. Caretta, K. Ritchter, M. Mann, A. Krone, R. Reeve, M. Weigand, P. Agrawal, P. Fischer, M. Kläui, G.S.D. Beach, Nature Materials <b>15</b>, 501 (2016).<br/>[3] S. Woo, K.M. Song, H.-S. Han, M.-S. Jung, M.-Y. Im, K.-S. Lee, K.S. Song, P. Fischer, J.-I. Hong, J W Choi, B.-C. Min, H. C. Koo, J. Chang, Nature Comm 8:15573 (2017)<br/>[4] H.-B. Braun, Advances in Physics <b>61</b> (1), 1-116 (2012).<br/>[5] A. N. Bogdanov and U. K. Rößler, Physical Review Letters <b>87</b> (3), 037203 (2001).<br/>[6] A. Fernández-Pacheco, R. Streubel, O. Fruchart, R. Hertel, P. Fischer and R. P. Cowburn, Nature Communications <b>8</b>, 15756 (2017).<br/>[7] Y. Liu, R. K. Lake and J. Zang, Phys Rev B <b>98</b> (17), 174437 (2018).<br/>[8] P. Sutcliffe, Journal of Physics A: Mathematical and Theoretical <b>51</b> (37), 375401 (2018).<br/>[9] N. Kent, R. Streubel, C.-H. Lambert, A. Ceballos, S.-G. Je, S. Dhuey, M.-Y. Im, F. Büttner, F. Hellman, S. Salahuddin and P. Fischer, Applied Physics Letters <b>115</b> (11), 112404 (2019).<br/>[10] N. Kent, N. Reynolds, D. Raftrey, I.T.G. Campbell, S. Virasawmy, S. Dhuey, R. V. Chopdekar, A. Hierro-Rodriguez, A. Sorrentino, E. Pereiro, S. Ferrer, F. Hellman, P. Sutcliffe, P. Fischer, Nature Communications 12 1562 (2021)<br/>[11] D, Raftrey and P. Fischer, Phys Rev Lett 127, 257201 (2021)