Electric-field-induced changes in magnetic moments and magnetic anisotropy in Co/MgO multilayer*

Voltage controlled magnetic anisotropy (VCMA) in Fe/MgO-based devices has been intensively studied [1]. One explanation for the VCMA is an induced change in orbital magnetic moment. However, electric field induced changes in orbital magnetic moment has never been confirmed experimentally. It has recently been pointed out the significance of the magnetic dipole T_z term to the VCMA in Pt with proximity-induced spin polarization [2]. In a Fe/Pt/MgO, the T_z term induction, correlating with electric quadrupole induction, induces a VCMA.
In this study, we report direct evidence of the electric-field-induced changes in orbital magnetic moment of Co ultrathin films in terms of in-situ X-ray magnetic circular dichroism spectroscopy [3]. In a Fe/Co/MgO multilayer, we find an induced change in orbital magnetic moment of 0.013μ_B in an electric field of ±0.2 V/nm. Moreover, the VCMA in the system is well estimated by the induced change. While we also found the magnetic dipole T_z term induction in Co, the induced T_z term only contributed little to the VCMA.
[1] T. Maruyama et al., Nat. Nanotechnol. 4, 158 (2009).
[2] S. Miwa et al., Nat. Commun. 8, 15848 (2017).
[3] T. Kawabe et al., arXiv 1708.08549.