Recent advances in nanocrystalline soft magnetic materials: A critical review for way forward

In this report, shortcomings in the recent trend of alloy development in nanocrystalline soft magnetic materials are discussed critically and suggestions for further improvement of the soft magnetic properties are given. Owing to the strong power dependence of the coercivity on the mean grain size, much emphasis tends to be placed primarily on reducing the grain size. While this approach is quite effective in reducing the effect of the magnetocrystalline anisotropy (K1) and the domain wall pinning effect is suppressed, this approach may have limited impact on the domain wall damping which governs the dynamic energy dissipation. Thus, the core loss could not be reduced solely by nano-scale grain refinement. Our recent study shows that the excess loss is suppressed dramatically by reducing the saturation magnetostriction (λs) to near zero. Thus, much attention should be paid to λs in addition to the common grain refinement approach in nanocrystalline soft magnetic alloys.