Abstract
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.
Highlights
The coupling between ferromagnetic and ferroelectric properties has recently attracted considerable attention toward the creation of novel devices using multiferroic controlling of their properties.[1–7] In particular, the hetero-interfaces in thin films comprising both ferromagnets and electrically polarized materials produce a rich variety of possibilities for creating multifunctional properties.[8–18] Modulation of interfacial lattice constants by an electric field (E) induces interfacial changes in magnetism
By applying E, the c-domain structures become dominant, from which it may be inferred that the application of the electric field, E, compresses the lattice constant of BaTiO3 and releases the strain in the Ni layer, thereby resulting in the magnetization in the in-plane easy axis in the Ni layers
The bright area indicates the a-domain structure. Both a- and c-domain structures without E are clearly observed, and they align to the c-domain structure by applying ±5 kV/cm, which is consistent with the magnetization
Summary
The coupling between ferromagnetic and ferroelectric properties has recently attracted considerable attention toward the creation of novel devices using multiferroic controlling of their properties.[1–7] In particular, the hetero-interfaces in thin films comprising both ferromagnets and electrically polarized materials produce a rich variety of possibilities for creating multifunctional properties.[8–18] Modulation of interfacial lattice constants by an electric field (E) induces interfacial changes in magnetism. The coupling between ferromagnetic and ferroelectric properties has recently attracted considerable attention toward the creation of novel devices using multiferroic controlling of their properties.[1–7]. The interfacial lattice distortion produces variations in magnetic properties, which are recognized as inverse magnetostriction effects.[19–23]. Magnetic anisotropy is tuned by lattice distortions. The magnetic anisotropy controlled by E has become an important subject in spintronics, which is the study aiming at the realization of devices operating with low energy consumption.[24–28]. Other approaches, which are our focus in this study, are based on the interfacial mechanical-strain coupling between ferromagnetic and ferroelectric layers using multiferroic hybrid structures. As one of the candidate approaches, applying E to BaTiO3 provides the possibility to tune the lattice constants by modulating the domain structures along the a- and c-axis directions by 3.992 and 4.036 Å, respectively, at room temperature.[29,30]
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