Neutron study of magnetic-moment distribution in Ni-Pt alloys

The average moments and the moment disturbances of ferromagnetic Ni-Pt alloys with concentrations of 20, 30, 40, 50, 55, and 57 at.% Pt have been measured by the magnetic diffuse scattering of neutrons. The data have been analyzed with the linear superposition model of Marshall including short-range order. The data have also been discussed in terms of Medina's chemical-magnetic environment model which assumes that the moment on an Ni atom is a function of the magnetic moments of the surrounding atoms and of its nearest chemical environment. The results show that the average Ni moment decreases with increasing Pt concentration, while Pt has an average moment of about half that of Ni. The moment disturbance functions, corrected for short-range order, show peaks in the forward direction corresponding to inhomogeneous-moment distributions which may be described as ferromagnetic clusters. The analysis of the data with the chemical-magnetic environment model shows that most of the moment disturbances are caused by the magnetic environment in accordance with other Ni-based alloys. An apparent difference in the macroscopic magnetization of these systems is attributed to differences in chemical short-range order rather than to a different mechanism for the onset of ferromagnetism.