Interfacial electronic structure-modulated magnetic anisotropy in Ta/CoFeB/MgO/Ta multilayers

We have observed several unexpected phenomena when a trace amount of Fe atoms is deposited onto the CoFeB/MgO interface in Ta/CoFeB/MgO/Ta multilayers. With the nominal thickness of the introduced Fe atoms (t_Fe) varying from 0 to 0.1-Å, the effective magnetic anisotropy energy (K _eff) of annealed multilayers is remarkably enhanced from 1.28-×-10^6-erg/cm³ to 2.14-×-10 ^6-erg/cm³. As t_Fe further increasing, the K_eff decreases and even becomes negative when t_Fe->-1- Å, indicating the change from perpendicular magnetic anisotropy to in-plane magnetic anisotropy. The analysis by X-ray photoelectron spectrometer reveals that the Fe atoms at annealed CoFeB/MgO interface show different electronic structures as t_Fe increasing, which combine with O atoms to form FeO_x (x-<-1), Fe₂O₃, and Fe ₃O₄, respectively, leading to modulation of Fe 3d-O 2p orbital hybridization and thus the K_eff. On the other hand, we find that the introduction of Fe atoms also helps to reduce the multilayers' magnetic damping.