Analysis of Magnetization Mechanism for NdFeB Magnet Using Spin-Polarized Scanning Electron Microscopy (Spin SEM)

The magnetization process of Nd-Fe-B bonded magnets prepared by the Hydrogenation-Disproportionation-Desorption-Recombination(HDDR) process was studied by observing magnetic domain structures using spin-polarized scanning electron microscopy (spin SEM). The positional relationship between the grain boundaries and the magnetic domain walls is clearly imaged. The result revealed that these magnets contain grains with a multi-domain structure in the thermally demagnetized state. The domain wall motions in grains with multi-domains are dominant in weak magnetic fields in the initial magnetization process, whereas fraction of the grains with a single domain increases with further increasing the magnetic field. The coercivity variations in these grains were also visualized.