Nd-Fe-B Hydrogenation-Disproportionation-Dehydrogenation-Recombination (HDDR) magnet for variable magnetic flux motor

The variable magnetic flux permanent magnet synchronous motor (VMF-PMSM) is one of the next-generation technologies to improve the efficiency of PMSM. VMF-PMSMs require the magnets with high magnetizability and reversal curve flatness. In this work, the high carbon content (Nd 0.9 Sm 0.1 )-Fe-B Hydrogenation-Disproportionation-Dehydrogenation-Recombination (HDDR) magnet with a fine grain size D 50 of 0.562 μm and a sharp grain size distribution ( D 90 - D 10 )/ D 50 of 0.806 was developed. Electron probe micro analyzer (EPMA) analysis shows the formation of R-Fe-Ga-C and R-Fe-B-C grain boundary phase in the high carbon content HDDR magnet, which is related to a densification while maintaining sub-μm size grains with sharp grain size distribution. First order reversal curve (FORC) analysis and Lorentz scanning transmission electron microscopy (Lorentz-STEM) suggest that the single-domain magnetization reversal is dominant to result in high magnetizability and reversal curve flatness.