Analysis of squareness in demagnetization curve of Nd–Fe–B magnet produced by the hydrogenation-disproportionation-desorption-recombination process

An analysis of squareness in demagnetization curve of Nd–Fe–B fine-grained alloys prepared by the hydrogenation-disproportionation-desorption-recombination (HDDR) process was carried out in reference to the melt-spun and sintered magnets by measurements of their recoil curves. The recoil curves of the HDDR magnet and the melt-spun magnet suggested that the magnetization process associated with the recoil behavior of the HDDR magnet is dominated by rotation of magnetization, while that of the sintered magnet suggested that domain wall movement is involved. The recoil susceptibilities for recoil curves that returns to nearly demagnetized state were 0.095 and 0.048T−1 in the isotropic and anisotropic HDDR magnets, respectively, when normalized by saturation magnetization. The normalized susceptibilities could be reproduced quantitatively, assuming that the magnetization recoil process within a grain in the HDDR magnet is described by the coherent rotation of magnetization and a simple model of orientation distribution of the easy axes. It appears that the anisotropic HDDR magnet has a wide distribution of orientation of the easy axes, which should be one of the reasons for poor squareness of the demagnetization curve of the HDDR magnet.