Relation between domain wall motion and coercivity in Nd-Fe-B sintered magnets prepared in various conditions

For the study of the relationship between the domain wall motion (DWM) and the coercivity in the samples of Dy-free Nd-Fe-B sintered magnets, the DC susceptibility (χDC) in the initial magnetization from the thermally demagnetized state and the DWM in the partially demagnetized state after the full magnetization in 5T-pulse field were measured. In the high coercivity (μ0Hc) samples of μ0Hc=1.35T and 1.62T, the stronger pinning in initial magnetization was detected as theχDC compared to other samples of the smaller coercivities such as μ0Hc=0.80T. The former samples also showed little DWM in the partially demagnetized state even the domain structures were clearly detected by magneto-force microscopy (MFM). In the latter samples, however, the obvious DWM was measured as the differences (∆M) between the magnetizations under applied field (Ma) and the remanences (Mr) in demagnetization process (∆M = Mr Ma). The pinning in DWM in initial magnetization process and the DWM in the partially demagnetized state are both originated from the interaction between the domain walls and grain boundary phases. The enhancement in coercivity, therefore, should come from the same interactions in the sintered samples.