Percolation calculations and a Mössbauer study of iron–platinum alloys with the FePt3 structure

Abstract

The magnetic properties of annealed iron–platinum alloys with 21–40 at.% Fe are different above and below a concentration of 30.5 at.% Fe. We show that this concentration corresponds to the percolation limit where Fe atoms on the face centres link the four corner atoms on that face into a cluster. Mössbauer spectra of 26.5 at.% Fe and 33.5 at.% Fe alloys confirm this model. The change in magnetic properties as alloys with less than 30.5 at.% Fe are cooled below the lower transition temperature is shown to correspond to a change from a fast relaxing regime to a static regime in which there is an incommensurate spin density wave.