Micromagnetic simulation of magnetizability of nanocomposite Nd-Fe-B magnets

Micromagnetic finite element calculations clearly show that the magnetizability of nanocomposite Nd2Fe14B magnets improves with increasing alpha-Fe content. The magnetization curves show a steep increase at the domain propagation field in de demagnetized samples. Thermally demagnetized states store a higher amount of exchange energy, leading to an increase of the initial susceptibility. An applied field of 960 kA/m leads to a saturation of 85% for a two-phase alpha-Fe/Nd2Fe14B magnet, whereas the Fe3B/Nd2Fe14B magnet and the single-phase Nd2Fe14B magnets reach a saturation of only 70% and 50%, respectively. The improved saturation behavior of two-phase alpha-Fe/Nd2Fe14B magnets has to be attributed to the exchange field which is provided by alpha-Fe grains that are already oriented parallel to the field direction. Hard magnetic grains that remain oppositely magnetized after applying the maximum magnetizing field deteriorate the coercive squareness in single-phase Nd2Fe14B magnets and two-phase Fe3B/Nd2Fe14B magnets. (C) 1998 American Institute of Physics. [S0021-9979(98)30711-2].