Propagation mechanism of magnetized and demagnetized regions in Nd–Fe–B sintered magnet

Nd–Fe–B sintered magnet is one of the most interesting materials especially for applications in EV and HV motor parts. This study deeply concerns to coercivity of the magnets, and that also relates to the serious Dy resource problem being watched recently. We investigated the magnetization and demagnetization mechanisms in commercial NEOMAX–48 magnet using EBSD, MFM, and Cs–TEM. The orientation of crystal grains mainly on c–plane (EBSD), domain structures of magnetized and demagnetized regions including the intermediate states (MFM), and the chemical composition and crystal and micro-structures including the thickness (Cs–TEM), all at the same position in the same magnet sample were studied. The propagation of magnetized and demagnetized regions surrounding the miss-orientated small number of grains was observed. The grain boundaries (GB) between (A) magnetized-magnetized grains and between (B) magnetized-demagnetized grains are similar thickness of 1.2−2.0 nm and similar amorphous structure including about 30 % of Fe, except the different oxygen contents of 10 % (A) and 40 % (B). As conclusion, the magnetic states of surface grains are mainly governed by the magnetic flux from the inside grains, and the GBs ((A) and (B)) have no specific different characteristics as chemical composition and crystal structure.