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 angstrom, the effective magnetic anisotropy energy (K-eff) of annealed multilayers is remarkably enhanced from 1.28 x 10(6) erg/cm(3) to 2.14 x10(6) erg/cm(3). As t(Fe) further increasing, the K-eff decreases and even becomes negative when t(Fe)>1 angstrom, 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 FeOx (x<1), Fe2O3, and Fe3O4, 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. (C) 2014 AIP Publishing LLC.