Hydrogen Pressure and Temperature Dependence of the Disproportionated State and Magnetic Anisotropy in the ${d}$ -HDDR Process of Nd–Fe–B–Ga–Nb Powders

Abstract

Nd–Fe–B-based alloy powders were subjected to the dynamic hydrogen disproportionation desorption recombination treatment and the effect of the hydrogen pressure and temperature conditions in the disproportination step on magnetic anisotropy as well as the state of disproportionated samples was investigated. Magnetic anisotropy was maximized when the sample was hydrogen disproportionated at 30 kPa and 800 °C–820 °C. The analyses of the X-ray diffraction (XRD) patterns showed that the iron boride phase formed during the hydrogen disproportionation step crystallized in the tetragonal structure. The lattice parameters and the peak intensity of this iron boride phase in XRD patterns varied depending on the disproportionation conditions. Both magnetic anisotropy and iron boride peak intensity became stronger when the disproportionation condition was close to the boundary of disproportionation and recombination reactions. These results suggest that there is some kind of relationship between magnetic anisotropy and the state of iron boride phase in disproportionated samples.