Mössbauer study of ferromagnetic phase transitions in (Pd1-xAgx)0.99Fe0.01 alloys

The effect of varying the host-matrix susceptibility of the Pd0.99Fe0.01 alloy system has been investigated through Mössbauer analysis of several (Pd1-xAgx)0.99Fe0.01 alloys with silver concentrations given by x=0, 0.005, 0.025, 0.10, 0.25, and 0.50. We have shown that the Curie temperature varies linearly with the spin paramagnetic susceptibility of the Pd-Ag host matrix, in agreement with theoretical predictions. This was done for silver concentrations up to 25 at.% and assumes a constant value for the spin of the iron impurity. From the observed linear dependence of the ordering temperature on the host-matrix susceptibility evaluated at Tc, we obtain a value for the exchange parameter of 0.11 0.01 eV which is used in estimating the saturation moment per iron atom. Assuming a molecular-field model, values for the saturation hyperfine field are deduced from temperature-extrapolated hyperfine-field measurements. Changes in those values with silver addition suggest changes in the polarization of 3d electrons and a possible correlation with the saturation magnetization. Isomer-shift measurements of these alloys are found to be concentration independent up to x=0.25 and to increase by 20% at about x=0.50.