Electric-field-induced changes of magnetic moments and magnetocrystalline anisotropy in ultrathin cobalt films

In this study, the microscopic origins of the voltage-controlled magnetic anisotropy (VCMA) in $3d$-ferromagnetic metals are revealed. Using in situ x-ray fluorescence spectroscopy that provides a high quantum efficiency, electric-field-induced changes in orbital magnetic moment and magnetic dipole ${T}_{\mathrm{z}}$ terms in ultrathin Co films are demonstrated. An orbital magnetic moment difference of $0.013\phantom{\rule{0.16em}{0ex}}{\ensuremath{\mu}}_{\mathrm{B}}$ was generated in the presence of electric fields of $\ifmmode\pm\else\textpm\fi{}0.2\phantom{\rule{0.16em}{0ex}}\mathrm{V}/\mathrm{nm}$. The VCMA of Co was properly estimated by the induced change in orbital magnetic moment, according to the perturbation theory model. The induced change in the magnetic dipole ${T}_{\mathrm{z}}$ term only slightly contributed to the VCMA in $3d$-ferromagnetic metals.