Crystal Structures and Permanent Magnet Properties of Fe–Pt Alloys

The relations between the order-disorder transformation and the permanent magnet properties of iron-platinum alloys have been investigated. The results show that the water-quenched alloy of γ single phase exhibits the typical soft magnetic properties. On aging at temperatures between about 770 and 870 K, the γ single phase transforms into a mixture of γ and γ1 phases, whose magnetization is not easily saturated for the high crystal magnetic anisotropy of the γ1 phase and the coercivity shows a low value. On aging at 903 K, the alloy of the γ1 single phase which gives rise to broad diffraction lines exhibits the highest value of Hc=135 kA·m−1. The ordering of the γ1 phase is advanced with the rise of aging temperature, while the coercivity rapidly falls.It is probable that the origin of the excellent permanent magnet properties of the Fe–Pt alloy is related to the existence of the very imperfect γ1 phase in regard to constitution and ordering, and these cause the pinning of the magnetic domain wall.