Evidence for a modulated ordering in the intermetallic compounds TbGe0,2Si0,8 and ErSi of CrB-type

Abstract
Neutron diffraction experiments have been performed on powder samples of TbGe0.2Si0.8 and ErSi. They order respectively at TN = 55 K and 11.5 K with a pure sine wave modulation propagating along the [100] direction of the orthorhombic unit cell. The wave vector k = [kx, 0, 1/2] is incommensurate with the lattice and is temperature dependent down to TIC (TIC = 43.5 K and 7.25 K respectively for TbGe0.2Si0.8, and ErSi) at which a magnetic transition to a commensurate phase described, by the wave vector k = [1/2, 0, 1/2] takes place. At any temperatures, the erbium magnetic moments are aligned along the a-axis, whereas for TbGe 0.2Si0.8, the terbium magnetic moments are in the (a, c) plane and make an angle of 20° with the c-axis