The exchange-coupling mechanism ofCr70Al30/Fe19Ni81bilayer films was investigated in terms of the crystallographic orientation, the interface roughness, and the grain size. The exchange-coupling fieldHexappears when theCr70Al30layer is thick enough to accommodate an antiferromagnetic domain wall. The value ofHexwas found to increase with decreasing the grain size in association with the [110] orientation. This tendency can be explained by considering the exchange-coupling field evaluated from the random field approximation. ©1997 American Institute of Physics.