Theory of the magnetic properties of dilute palladium-iron alloys

Abstract

The dynamic properties of dilute alloys of iron in palladium and palladium alloys are investigated on the basis of a model in which a local spin on the iron atom magnetizes the surrounding matrix via a coupling of strength J , leading to a prediction of the spin wave spectrum at long wavelengths. The parameters of the model are first established by considering the static properties where it is found that, within a linear response approximation, the model leads to a very simple relation between the induced ‘giant' moment and the suscepti­bility of the matrix which is shown to be in reasonable agreement with experiment. Extension of this relation to the high temperature susceptibility of the alloys also fits the experi­mental data over a wide temperature range. The two analyses lead to a consistent value for the interaction parameter J , of J = 0⋅15 ± 0⋅02 eV. It is found that the spin wave spectrum in the low temperature ferromagnetic state may be derived in terms of a frequency dependent Ruderman-Kittel interaction between iron spins which leads to the appearance of an optical mode spin wave branch in addition to the usual acoustic spin wave mode. The energy of the long wave optical mode is predicted to be proportional to be proportional to iron concentration and to have a value of 0⋅015 eV for a 1% Pd-Fe alloy.