Temperature dependent neutron depolarization studies on hard magnetic Nd15Fe77B8 alloys

Three-dimensional neutron depolarization measurements have been carried out in order to investigate the temperature-dependent domain structure of sintered Nd-Fe-B samples. Different thin (0.2-mm) field-demagnetized slabs were studied in the temperature range between 4.2 K and room temperature. On cooling down the sample the mean domain size starts to increase at about 170 K where the anisotropy constant K₂ becomes larger than K₁. At the spin orientation point around 130 K no sharp discontinuity of the domain structure could be detected, but the temperature-dependence of the domain size shows the same tendency as the total anisotropy constant 2(K₁+2K₂). In the entire temperature range there are several domains within one grain. Furthermore, the grain alignment due to the application of an external magnetic field during the fabrication process could be sensitively detected.