New magnetic phenomena in TbNi2

Structural investigations at room temperature revealed that TbNi2 does not crystallize in the Laves phase structure, but shows a superstructure of the Laves phase with the space group F-43m. Susceptibility, specific heat, mag netostriction and magnetoresistance measurements on polycrystalline specime ns showed an additional magnetic phase transition at T-R = 14 K below the C urie temperature of T-C = 36 +/- 0.2 K. In order to clarify the nature of t his magnetic phase transition at 14 K, elastic neutron diffraction below an d above T-R and Te was performed. The analysis of these data showed that th is transition at T-R is due to the rotation of the Tb moments on three of t he total of eight non-equivalent Tb sites in the rhombohedrally distorted u nit cell in the magnetic ordered state. This rotation of these Tb moments i s out of the [1111] direction into a plane perpendicular to the space diago nal. The cause for this magnetic instability is due to an interplay of the regularly arranged vacancies in the superstructure and the crystal field le vel position which has been studied by inelastic neutron scattering.