Enhancement of perpendicular magnetic anisotropy of ferromagnet/oxide heterointerface by an oxygen-dependent orbital modulation

Abstract

Tailoring the magnetic anisotropy of a ferromagnet film is the critical issue to construct high-efficient magnetic memory and logic devices. In this paper, we demonstrated a controllable magnetic anisotropy of Pt/Co/HfO2 multilayers by tuning the oxygen-dependent orbital occupancy at the Co/HfO2 interface. Driven by the large difference in formation enthalpy between HfO2 with CoO, an effective O2- migration occurred at the Co/HfO2 interface by thermal activation, which increased the electronic occupation on the Co 3dz2 orbit and facilitated the out-of-plane Co-O orbital hybridization. Therefore, the interfacial magnetic anisotropy energy was enhanced by two times, leading to a transition from in-plane to out-of-plane anisotropy. Conversely, the O2- migration was suppressed when HfO2 was replaced by ZnO with the formation enthalpy close to CoO, which makes the orbital tunability effect disappear and the magnetic anisotropy of film unchangeable. These findings are crucial for exploiting the magnetoionic control of interfacial magnetism and advancing the functionalized design of memorizers based on orbital engineering.