Effects of anisotropy field dispersion and grain boundary on coercivity and squareness ratio for HDDR-processed NdFeB powders

In this study, we simulated the effects of the anisotropy field (Hk) dispersion of the grains (the main phases and the deterioration layers) for a NdFeB magnetic powder on Hc and squareness ratio in consideration of the magnetic properties of the grain boundaries and the deterioration layer of the grain surface using a micromagnetic simulator. The Hc decreases as increasing the coefficient variation of Hk (σHk/; σHk: standard deviation, : average) of the grain for the soft magnetic grain boundary, however, is independent of the σHk/ for the non-magnetic grain boundary. The squareness ratio is 1.0 up to a σHk/ of 25% for the soft magnetic grain boundary, however, decreases as the σHk/ increases for the non-magnetic grain boundary. Comparing the calculation and experimental values, when the grain boundary was non-magnetic and the σHk/ was 25 to 30%, the Hc and the squareness ratio were close to the experimental values.