Diffuse neutron scattering measurements were performed on quenched alloys with x = 0.31, 0.36, 0.39, 0.43 and 0.5, which belong to the transition region between ferromagnetism and antiferromagnetism. The nuclear and magnetic cross sections were separated, and Cowley short-range order atomic parameters determined. It was found that the superantiferromagnetic behaviour of these alloys occurred owing to the existence of the antiferromagnetic clusters of the -FeMn type caused by short-range order regions of the CuAu type.