Voltage-controlled magnetic anisotropy in an ultrathin nickel film studied by operando x-ray magnetic circular dichroism spectroscopy

Abstract

Voltage-controlled magnetic anisotropy (VCMA) in an atomically thin Ni film placed at an epitaxial Fe-MgO interface has been studied. We characterize the VCMA by employing Fe/Ni/MgO-based magnetic tunnel junction. Moreover, we conduct x-ray magnetic circular dichroism (XMCD) spectroscopy around Ni absorption edges under an external voltage application to the tunnel junction device. This operando XMCD spectroscopy demonstrates voltage-induced changes of orbital and effective spin magnetic moments of Ni. As compared with the previous study, where operando XMCD spectroscopy was performed on an atomically thin Co film, we find that the magnitude of the VCMA effect in Ni and Co is proportional to the voltage-induced change of the orbital magnetic moment. This study would lead to a comprehensive understanding of how an electric field affects interfacial magnetism in ferromagnetic metals.