Different oxygen migration behaviors at CoFe/MgO and CoFe/HfO2interfaces 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.