A neutron depolarization study on dysprosium and terbium

Abstract

The neutron depolarization of a polycrystalline 0.25 mm thick dysprosium foil has been measured in the temperature range from 4.2° to 300°K in external magnetic fields up to 2.2 kOe. From 85° to ∼ 130°K, where Dy should behave as an antiferromagnet, domains with a net magnetic moment were found to exist in the antiferromagnetic material. Above 130°K the depolarization effect is very small, indicating that only a few domains are present. In the ferromagnetic region ( T < 85°K) the calculation of the domain size from the depolarization data is possible. The domains were found to be very small (∼ 10 −6 −5 × 10 −5 cm) and grew with the applied field, H, as expected. If the sample is cooled in zero field and then H is applied, a sort of internal coercive force for the Blochwall mobility is observed. The depolarization and, hence, the size of the domains were found to be very sensitive on the magnetic field acting on the sample during the cooling process. The depolarization measurements on terbium were combined with measurements of the small angle scattering, so that the induction, B, in the domains and the mean domain size were obtained separately. The values B found in this way are lower than those corresponding to the saturation magnetization.