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 100.3em0exnm, their coercivity is rather high, 20--300.3em0exOe. 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.