Short range magnetic order in gamma-manganese alloys

Abstract

The temperature variation of the intensity of the diffuse peak observed near the (100) position in powder neutron diffraction patterns of an equiatomic γ-MnFe alloy and of several Mn-rich γ-MnCu alloys has been measured. The intensity of the diffuse peak reaches a maximum at the Neel points of the alloys which are antiferromagnetic and approaches zero at 4.2 K for equiatomic MnFe but not for the MnCu alloys. The results of both double axis and triple axis neutron diffractometry of paramagnetic and antiferromagnetic alloys suggest that the diffuse peak is mainly due to static or quasistatic short range order. Comparison of the neutron and X-ray patterns of an 82 at.% MnAu alloy showed that less than 10% of the diffuse peak observed in the neutron pattern could be due to atomic short range order. No change was observed in the diffuse (100) peak in the neutron diffraction patterns of a 68 at.% γ-MnCu null matrix alloy after heating, although considerable atomic clustering was revealed