The effect of coherent uniaxial anisotropies on the grain-size dependence of coercivity in nanocrystalline soft magnetic alloys

The grain-size (D) dependence of coercivity (H_c) in various nanocrystalline soft magnetic materials has been reanalyzed with particular attention to induced uniaxial anisotropies. In addition to the well-known D⁶ law, a D³ dependence of H_c is observed for some nanocrystalline samples with uniaxial anisotropies larger than the random magnetocrystalline anisotropy (〈K₁〉). The original random anisotropy model has been extended to the case where the macroscopic uniaxial anisotropies dominate over 〈K₁〉. As a result, the extended model predicts a D³ dependence of H_c and explains the observed grain-size dependence quite well.