  Controlling magnetic anisotropy by orbital magnetic moments related to
interfacial strains has considerable potential for the development of future
devices using spins and orbitals. For the fundamental physics, the relationship
between strain and orbital magnetic moment is still unknown, because there are
few tools to probe changes of orbital magnetic moment. In this study, we
developed an electric-field- (E)-induced X-ray magnetic circular dichroism
(EXMCD) technique to apply E to a ferroelectric BaTiO3 substrate. We reversibly
tuned the interfacial lattice constants of Ni/Cu multilayers on BaTiO3 using
this technique. As the domain structures in BaTiO3 are modulated by E, EXMCD
measurements reveal that the changes in the magnetic anisotropy of Ni/Cu films
are induced through the modulation of orbital magnetic moments in Ni with
magneto-elastic contributions. The strained Ni layer that induces the
perpendicular magnetic anisotropy without E is released at E = 8 kV/cm, and
in-plane magnetization also occurs. We observed that EXMCD measurements
clarified the origin of the reversible changes in perpendicular magnetic
anisotropy and established the relationship between macroscopic inverse
magnetostriction effects and microscopic orbital moment anisotropy.
