Microscopic origin of voltage-controlled magnetic anisotropy in FePt/MgO epitaxial multilayer*

Spin-transfer has surpassed current-induced magnetic fields as the preferred technology for magnetization switching in nanoscale magnets. However, spin-transfer switching exhibits Joule heating that remains too large to ignore. Thus, a novel method offering magnetization control without electric current is highly desirable. Because voltage-controlled magnetic anisotropy (VCMA) in Fe/MgO-based devices [1] can be an ultimate technology for spintronics devices, a novel method to increase the VCMA is important.
In this study, we will show a new mechanism to enhance VCMA in FePt/MgO epitaxial tunnel junction device proved by X-ray magnetic circular dichroism spectroscopy [2]. Electric field at metal/dielectric interface couples with a electrric quadrupole of an electron shell in metals. The induced electric quadrupole produces the intra-atomic magnetic dipole T_z term and influences magnetic anisotropy through spin-flip process. Our finding enables the design of novel materials showing VCMA larger by more than a factor of 10.
[1] T. Maruyama et al., Nat. Nanotechnol. 4, 151 (2009).
[2] S. Miwa et al., Nat. Commun. 8, 15848 (2017).ua