Takamasa Usami1,Shumpei Fujii1,Yu Shiratsuchi1,Amran Yatmeidhy2,Shinya Yamada1,Takeshi Kanashima1,Ryoichi Nakatani1,Yoshihiro Gohda2,1,Kohei Hamaya1
Osaka University1,Tokyo Institute of Technology2
Takamasa Usami1,Shumpei Fujii1,Yu Shiratsuchi1,Amran Yatmeidhy2,Shinya Yamada1,Takeshi Kanashima1,Ryoichi Nakatani1,Yoshihiro Gohda2,1,Kohei Hamaya1
Osaka University1,Tokyo Institute of Technology2
The use of ferromagnetic/ferroelectric interfacial multiferroic heterostructures in spintronics devices is expected as a highly efficient method for controlling magnetization vectors by an electric-field (<i>E</i>) [1]. To incorporate the multiferroic heterostructure into the low-power consumption devices, a giant converse magnetoelectric (CME) effect is needed, where the CME coupling coefficient over 10<sup>-5</sup> s/m is required. In this study, we report giant CME coupling coefficients over 10<sup>-5</sup> s/m in the multiferroic heterostructures with ferromagnetic Co<sub>2</sub>-Heusler alloys that are famous as spintronic materials having high spin polarization [2,3].<br/>30-nm-thick Co<sub>2</sub>-Heusler-alloy films (Co<sub>2</sub>FeSi, Co<sub>2</sub>FeAl<sub>0.5</sub>Si<sub>0.5</sub>, Co<sub>2</sub>Fe<sub>0.4</sub>Mn<sub>0.6</sub>Si, and Co<sub>2</sub>MnSi) were grown on (011)-oriented Pb(Mg<sub>1/3</sub>Nb<sub>2/3</sub>)O<sub>3</sub>-PbTiO<sub>3</sub> (PMN-PT) substrates with inserting a 0.3-nm-thick Fe layer by molecular beam epitaxy at 300 °C. As a reference, ferromagnetic Fe<sub>3</sub>Si (Fe<sub>2</sub>FeSi) was also grown on PMN-PT(011). XRD measurements revealed that all the Heusler films are polycrystalline. In addition, we confirmed that the <i>L</i>2<sub>1</sub> or <i>D</i>0<sub>3</sub>-ordered structures are included in Co<sub>2</sub>FeSi, Co<sub>2</sub>Fe<sub>0.4</sub>Mn<sub>0.6</sub>Si, and Fe<sub>3</sub>Si films whereas only the <i>B</i>2-ordered structure is obtained in Co<sub>2</sub>FeAl<sub>0.5</sub>Si<sub>0.5</sub> and Co<sub>2</sub>MnSi films.<br/>The CME effect was characterized by in-plane magneto-optical Kerr-ellipticity measurements and conventional magnetization measurements at room temperature [3]. We found that all multiferroic heterostructures using Co<sub>2</sub>-Heusler-alloy films show the 90° rotation of the magnetic easy axis by applying <i>E</i>. In addition, a giant CME coefficient over 10<sup>-5</sup> s/m was obtained for all the Co<sub>2</sub>-Heusler/PMN-PT(011) multiferroic heterostructures. For the Fe<sub>3</sub>Si/PMN-PT(011), on the other hand, a small variation in the magnetic easy axis was seen. This study indicates that the presence of Co atoms in Heusler alloys is important to demonstrate the giant CME effect. We note that the use of Co<sub>2</sub>-Heusler alloys is also useful to achieve high-performance spintronics devices.<br/>This work was partly supported by JST CREST Grant No. JPMJCR18J1 and JSPS KAKENHI Grant No. JP21K14196 and JP19H05616.<br/><br/><br/>[1] J. M. Hu <i>et al</i>., Nat. Commun. <b>2</b>, 553 (2011).<br/>[2] T. Usami <i>et al</i>., Appl. Phys. Lett. <b>118</b>, 142402 (2021).<br/>[3] S. Fujii <i>et al</i>., NPG Asia Mater. <b>14</b>, 43 (2022).