Magnetism and microstructure in nanocrystalline FeCoZr ferromagnets

Coercivity Hc, the initial susceptibility χo, and the Rayleigh constant α of metallic nanocrystalline ferromagnets produced by annealing of an amorphous Fe60Co30Zr10 alloy above the crystallization temperature is investigated as a function of the grain size d. It is shown that Hc and χo follows a d6 and a d−6 power law, respectively. The grain size dependence of the magnetic properties and the temperature dependence of Hc are discussed within the framework of the random anisotropy model. For small magnetic fields H < 0.5Hc, the magnetization curves of nanocrystalline ferromagnets obey Rayleigh's law. The experimental relation between Hc, χo, and the Rayleigh constant α shows good agreement with the statistical potential theory.