Hysteresis loops and the demagnetization process at 4.2 K for melt-spun Nd13Fe77B10

Hysteresis loops of melt-spun Nd13Fe77B10 cooled down at the remanent state were measured at 4.2 K. The loop for fields of Hmax=6.4 MA m-1 is characterized by low- and high-field steps. The loop for fields of Hmax=4.0 MA m-1 is very thin with only a low-field step and is shifted profoundly along the H-axes. The loops and the spin distribution during the demagnetization process were analysed by micromagnetic finite-element calculations. Quantitatively, the calculations reproduce the experimental loops fairly well. The spin distribution is fairly nonuniform, and a domain-wall-like distribution appears not only at some grain boundaries but also within some grains at the high-field step. The demagnetization proceeds by nonuniform reversion as a whole, and neither the model of single-domain reversion nor the model of domain-wall pinning in the grain boundary model describes the process appropriately. (author)