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 (tFe) varying from 0 to 0.1 Å, the effective magnetic anisotropy energy (Keff) of annealed multilayers is remarkably enhanced from 1.28 × 106 erg/cm3 to 2.14 × 106 erg/cm3. As tFe further increasing, the Keff decreases and even becomes negative when tFe > 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 tFe increasing, which combine with O atoms to form FeOx (x < 1), Fe2O3, and Fe3O4, respectively, leading to modulation of Fe 3d-O 2p orbital hybridization and thus the Keff. On the other hand, we find that the introduction of Fe atoms also helps to reduce the multilayers' magnetic damping.