Thermal expansion anomalies and spontaneous magnetostriction in Tm 2Co 7

Abstract

The temperature dependencies of the lattice parameters and magnetization have been studied in the intermetallic compound Tm 2Co 7. Magnetic ordering is accompanied by spontaneous magnetostriction in the basal plane and along the c axis (2.0 × 10 −3 and 2.7 × 10 −3 respectively at 5 K). This corresponds to a volume effect ω s = 6.6 × 10 −3. The Tm atoms on the quasi-cubic sites are considered to be responsible for the spin reorientation from the uniaxial type of magnetic anisotropy above 45 K to the cone of easy axes below this temperature, which is explained by magnetoelastic effects. In the cone range a large orthorhombic distortion ϵ (up to −3.5 × 10 −3 at 5 K) is observed. The additional volume anomaly δω s = −1 × 10 −3, which accompanies spin reorientation, can be explained by the anisotropy of the magnetic moments of the thulium and cobalt sublattices.