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

摘要

In this study, we simulated the effects of the anisotropy field ( H sub k /sub) dispersion of the grains (the main phases and the deterioration layers) for a NdFeB magnetic powder on H sub c /sub 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 H sub c /sub decreases as increasing the coefficient variation of H sub k /sub ( σH sub k /sub / k /sub ; σH sub k /sub: standard deviation, k /sub : average) of the grain for the soft magnetic grain boundary, however, is independent of the σH sub k /sub / k /sub for the non-magnetic grain boundary. The squareness ratio is 1.0 up to a σH sub k /sub / k /sub of 25% for the soft magnetic grain boundary, however, decreases as the σH sub k /sub / k /sub increases for the non-magnetic grain boundary. Comparing the calculation and experimental values, when the grain boundary was non-magnetic and the σH sub k /sub / k /sub was 25 to 30%, the H sub c /sub and the squareness ratio were close to the experimental values.