Electric field effects on magnetism in metals have attracted widespread attention, but the microscopic mechanism is still controversial. We experimentally show the relevancy between the electric field effect on magnetism and on the electronic structure in Pt in a ferromagnetic state using element-specific measurements: x-ray magnetic circular dichroism (XMCD) and x-ray absorption spectroscopy (XAS). Electric fields are applied to the surface of ultrathin metallic Pt, in which a magnetic moment is induced by the ferromagnetic proximity effect resulting from a Co underlayer. XMCD and XAS measurements performed under the application of electric fields reveal that both the spin and orbital magnetic moments of Pt atoms are electrically modulated, which can be explained not only by the electric-field-induced shift of the Fermi level but also by the change in the orbital hybridizations.

In this study, we have investigated perpendicular magnetic anisotropy in a MgO/Co/Pt structure under an electric field. The change in the interface anisotropy energy in a MgO/Co stack upon the application of a gate voltage was determined by using a transport measurement technique. The result indicates that a decrease in the electron number at the surface of the Co layer leads to the enhancement of the perpendicular anisotropy energy at a temperature sufficiently lower than the Curie temperature.

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