Dilute PdNi-a homogeneous magnetic system of fluctuating moments

It is shown that published magnetic susceptibility and magnetisation data for PdNi alloys are consistent with a homogeneous model in which the Ni atoms have a spin fluctuation temperature Ts approximately 55K and are coupled by ferromagnetic Ni-Ni interactions. Using a molecular-field model the equivalent classical RMS moment per Ni atom square root ( mu 2) is shown to be concentration independent for concentrations between 1.3 and 16.7 at.% Ni and for temperatures between the ordering temperature Tc and 700K. square root ( mu 2) exhibits a temperature-dependent exchange enhancement at high temperatures, and at low temperatures falls to zero due to intrinsic spin fluctuations. The exchange enhancement and the ferromagnetic coupling between Ni moments are shown to be related in accordance with the indirect-coupling model of Takahashi and Shimizu (1965). The critical concentration for the onset of ferromagnetism and the concentration dependence of the ordering temperature Tc are determined from the curve for square root ( mu 2) and are shown to be in excellent agreement with experiment. A simple model is presented which qualitatively reproduces the magnetisation curves for paramagnetic and ferromagnetic alloys.