We report thermal expansion measurements carried out on a single-crystal of the giant magnetocaloric effect material Gd
5(Si
0.43Ge
0.57)
4. At the magneto-structural phase transition at
T0
240K, large steps in the relative length change
ΔL/L along the principle crystallographic axes are observed. The single-step behaviour in
ΔL/L indicates that the magnetic and the 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
dT0/dP of 3.2±0.2K/kbar. The pressure effect is strongly anisotropic as follows from the anisotropy in the linear thermal expansion. Uniaxial pressure along the
a-axis enhances
T0, while uniaxial pressure in the
bc-plane suppresses
T0.