Co-existence of biquadratic and unidirectional anisotropy in IrMn/CoFe/Fe[O.sub.x]/CoFe films

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