High field magnetic properties of Fe-Pt Invar alloys

The magnetization and high-field susceptability of a series of Fe 3Pt alloys have been investigated as a function of composition and degree of atomic ordering. The magnetization results indicate that these alloys cannot be described in terms of the model of very weak itinerant ferromagnetism. Instead, the data are fitted by a model which includes a magnetoelastic term, leading in turn to a discussion of the magnetovolume relations in the Invar problem. The high-field susceptability is large, as in other Invars, and dependent of the degree of ordering. A minimum is observed at 30 at% Pt in both the ordered and disordered phases. From the existence of the minimum it is suggested that FePt ferrimagnetic interactions may be induced in Pt-richer alloys by a distortion of the cubic lattice. In general, the Fe 3Pt alloys constitute a unique case among all the alloys characterized by Invar anomalies, and cannot be used to typify Invar behaviour.