Thermal expansion of the magnetorefrigerant Gd5(Si,Ge)4

Abstract

We report thermal expansion measurements carried out on a single-crystal of the giant magnetocaloric effect material Gd5(Si0.43Ge0.57)4. At the magneto-structural phase transition at T_0 ~ 240 K, large steps in the relative length change DELTAL/L along the principle crystallographic axes are observed. The single-step behaviour in DELTAL/L indicates that the magnetic and structural phase transition occur at one and the same temperature. The specific heat was measured in order to determine the latent heat. Using the Clausius-Clapeyron relation we extract a hydrostatic pressure dependence dT_0/dp of 3.2+-0.2 K/kbar. The pressure effect is strongly anisotropic as follows from the anisotropy in the linear thermal expansion. Uniaxial pressure along the a-axis enhances T_0, while uniaxial pressure in the bc-plane suppresses T_0.