Study of the spin reorientation phenomenon in Nd2(Fe,Si)14BHy

Abstract We have studied the influence of the Si for Fe substitution and of the H insertion on the spin reorientation phenomenon in the Nd 2 Fe 14 B phases. To determine the temperature of spin reorientation and the tilt angle between the c -axis and the easy magnetisation direction, we have measured the angular dependence of the components of the magnetisation vector. Our measurements are based on powder samples that have been previously aligned under an external magnetic field. The Si for Fe substitution induces a decrease of the spin reorientation temperature and of the tilt angle. Meanwhile, we have found that the tilt angles are almost the same for Nd 2 Fe 13 SiB and Nd 2 Fe 12 Si 2 B. These features are analysed in terms of changes in the crystal electric field and the unit cell volume induced by the Si for Fe substitution. The insertion of hydrogen in the Si-containing samples leads to an additive decrease of the spin reorientation temperature. This decrease is not linked to a change in the tilt angle at 4 K but to a different thermal behaviour in the H-containing samples. The magnitude of the effects of H insertion on the crystal electric field in comparison with the Si for Fe substitution is discussed together with the role of the lattice expansion.