Characteristic magnetovolume effects in Invar type Fe-Pt alloys

The thermal expansion and the forced volume magnetostriction have been measured for the Invar type Fe-Pt alloys. Derived values of the spontaneous volume magnetostriction are large and the same order of magnitude as those for the Fe-Ni Invar alloys. Their dependence on concentration and chemical ordering can be explained by the change of Fe-Fe atom pairs and their temperature dependence satisfies the empirical relation, omega s (T)=CM 2 (T). The forced volume magnetostriction observed at 4.2K is about one order smaller than that for Fe-Ni Invar alloys. This suggests the presence of strong ferromagnetism in Fe-Pt Invar alloys, although this contradicts the observation of large values for the high-field susceptibility in these alloys.