Angular dependence of coercivity and exchange bias in IrMn/CoFe bilayers

Abstract We report on a study of the angular dependence of the exchange field ( H E ) and the coercivity ( H C ) of IrMn( t AF )/CoFe (100 A), with t AF = 30 and 50 A, as a function of the angle at which the external field is applied relative to the easy direction of the unidirectional anisotropy. We find that the exchange and coercivity have different rotational symmetries with H E being unidirectional and H C uniaxial. Our data is consistent with a model of exchange anisotropy in which H E is derived from the degree of order in the antiferromagnet and H C arises due to interfacial effects. Also H E and H C have different symmetries and can be described by Fourier cosine series.