Different oxygen migration behaviors at CoFe/MgO and CoFe/HfO2 interfaces and their effects on the magnetic anisotropy

Abstract

We have studied annealing-induced oxygen migration at CoFe/MgO and CoFe/HfO2 interfaces and its effect on the magnetic anisotropy of Ta/CoFe/MgO (HfO2) films. Through x-ray photoelectron spectroscopy, we found that the Fe–O bonds exist at both CoFe/MgO and CoFe/HfO2 interfaces at the as-deposited state due to the oxidation of interfacial Fe atoms during the deposition of the MgO and HfO2 layers. After annealing, the amount of the Fe–O bonds at the CoFe/MgO interface decreases, whereas at the CoFe/HfO2 interface, it increases, indicating that the oxygen atoms migrate from Fe–O bonds to MgO layers at the CoFe/MgO interface, whereas they migrate from the HfO2 layer to Fe–O bonds at the CoFe/HfO2 interface. Correspondingly, the magnetic anisotropy energy decreases in the Ta/CoFe/MgO film but increases in the Ta/CoFe/HfO2 film after annealing. We attributed these results to interfacial Fe 3d–O 2p orbital hybridization modulated by different oxygen migration behaviors. Our results may improve the understanding of the oxygen migration effect on magnetic anisotropy and anomalous Hall sensitivity in ferromagnet/oxide heterostructures.