Soft magnetism in mechanically alloyed nanocrystalline materials

We study the magnetic properties of nanocrystalline Fe80Cu20 (at. %) and Fe92Al2Si6 (wt %) alloy powders prepared by mechanical alloying. Although these powders have crystallite sizes of approximately 10 nm, their coercivity is rather high, 20-30 Oe. We demonstrate that the main contribution to the coercivity in mechanically alloyed powders arises from the long-range fluctuations in the residual stress, which couples to total anisotropy factor via the magnetostriction of the alloy. The residual stress can be partially reduced by annealing within a narrow temperature range. We have modified the "random anisotropy model" to take into account the residual stress in the mechanically alloyed nanocrystalline powders.