Relation between the Exchange-Coupling Field and the Grain Size in Cr70Al30/Fe19Ni81 Bilayers

The exchange-coupling mechanism of Cr70Al30/Fe19Ni81 bilayer films was investigated in terms of the crystallographic orientation, interface roughness, and grain size. The exchange-coupling field Hex appears when the Cr70Al30 layer is thick enough to accommodate the one-dimensional antiferromagnetic domain wall. The value of Hex decreases with an increase in the degree of the <110> orientations associated with the grain growth, but increases with increasing the interface roughness. These results can be qualitatively explained by considering the exchange-coupling field evaluated from the random field approximation.