The arrangement of Mn atoms in re-entrant spin glass of FCC Au-Mn alloys

Abstract

The intensity of X-ray diffuse scattering was measured at room temperature for FCC Au-Mn alloys whose compositions are less than 15 at.% Mn. A quick survey by electron diffraction had shown the existence of diffuse scattering from atomic short-range order (ASRO). From an analysis for a Au-15.0 at.% Mn alloy on the basis of the observed ASRO parameters, the Mn atoms in the ASRO state were found to form a three-dimensional irregular network which is linked by linear chains along the (100) directions. Assuming that the first-nearest Mn-Mn pairs have antiferromagnetic coupling, while those at the second-neighbour distance are ferromagnetically coupled, a spin configuration was assigned to this irregular Mn network: several types of ferromagnetic clusters were found to exist, and they are connected with one another by antiferromagnetic coupling. It is occasionally found that there are some Mn atoms whose spin orientation is difficult to define because they are linked by antiferromagnetic coupling on one side and ferromagnetic coupling on the other side. Such a coupling of clusters seems to be responsible for the characteristic magnetic behaviour at low temperature, i.e. re-entrant spin-glass behaviour.