Abstract
We observed the coexistence of biquadratic and unidirectional anisotropy in the CoFe layer by inserting the nano-oxide-layer FeO x in the IrMn/CoFe bilayers. Analyses of X-ray magnetic circular dichroism suggested that the FeO x possessed ferromagnetic components. Mixed valence states of Fe, Fe 2+ and Fe 3+ were observed in the FeO x layer, which implied that both antiferromagnetic and ferromagnetic components might co-exist in the FeO x layer. The uniaxial anisotropy in CoFe at 90° may originate from the interaction of CoFe with the antiferromagnetic components of the FeO x layer in the presence of interfacial magnetic roughness. The unidirectional anisotropy at 0° may result from the exchange biasing from the IrMn layer through the ferromagnetic components in the FeO x layer. © 2005 IEEE.