Co-existence of biquadratic and unidirectional anisotropy in IrMn/CoFe/FeO/sub x//CoFe films

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