Effects of Anisotropy Field and Easy Axis Dispersions on Squareness Ratio for HDDR-Processed Nd-Fe-B Powders

Nd-Fe-B magnetic powders produced by the hydrogenation-decomposition-desorption-recombination process have a lower squareness ratio than sintered magnets. In this paper, the anisotropy field (H
_k
) distribution was assumed to be a horizontally flipped lognormal distribution and the effect of the H
_k
dispersion on the squareness ratio was investigated by using a micromagnetic simulator. As a result, the squareness ratio was very similar to the experimental demagnetization loop, when (H
_k
) was 5500 kA/m and σ H
_k
/(H
_k
) was 30%. Moreover, we investigated the easy axis dispersion of grains on squareness ratio in consideration of soft magnetic or nonmagnetic grain boundaries. As a result, the squareness ratio for the nonmagnetic grain boundary was closer to the experimental value; however, it is difficult to describe the experimental demagnetization loop by only considering the easy axis dispersion.