Katsuhiko Wakayama

Ferromagnetism and structural distortions induced in atomized Fe-AI (35–42 at.% AI) powder particles by cold milling

Abstract Micrometre-sized particles of Fe1−x Al x (x = 0.35 − 0.42) powder prepared by the atomizing method have been investigated by magnetization measurement and high-resolution transmission electron microscopy. As-atomized particles are paramagnetic and they consist of a few grains of the B2 structure. Cold milling for several hours magnetizes the particles to a spontaneous magnetization as great as 100emu g−1. The milled particles become flakes composed of lamellae, expanding parallel to the (110) plane and having a heavily distorted lattice. The lamella has a mosaic structure consisting of nanometre-sized grains whose boundaries are frequently antiphase with large numbers of Fe-Fe nearest couplings, which may be at the origin of ferromagnetism in cold-worked powders. When the milled powder is heated for a time as short as 1 min at 100–400°C, the lattice distortion is relaxed by recrystallization of the nano-grains. the lamella being kept, and consequently the magnetization decreases to a few emu g−1.