Magnetic and Magnetovolume Properties of the Cu₃Au Type Ordered Fe-Pt Alloys around the γ- α Phase Boundary

Magnetization, thermal expansion and forced volume magnetostriction have been measured for Fe 1- x Pt x ordered alloys ( x =0.23 –0.27). In the fcc alloys ( x ≧0.25), the atomic moment and the spontaneous volume magnetostriction increase monotonically with decreasing x , implying the Fe-Pt Invar alloys to be homogeneous and strong ferromagnets even around the γ- α phase boundary. On the other hand, the magnetic moment of the α phase ( x <0.25) is a little larger than that of the γ phase, suggesting a very weak magnetic field dependence of the M s temperature. The observed large spontaneous volume magnetostriction may play an important role in determining the favorable conditions for the thermoelastic martensite transformation in the Fe-Pt alloys.