Thermal expansion, forced magnetostriction, and pressure dependence of the Néel temperature in GdCu2 and TbCu2

Magnetovolume experiments are reported on the antiferromagnetic GdCu2 and TbCu2 compounds. The thermal expansion below the Néel temperature shows large contributions of magnetic origin to the volume. The spontaneous volume magnetostriction is negative and amounts to −1.1 × 10−3 for GdCu2. At the spin flip transition at 4.2 K in both the compounds an increase in volume is observed also of the order of 10−3. From these experiments a negative value is derived for the volume derivative of the antiferromagnetic interaction parameter, in contradiction to the positive value that follows from the pressure dependence of the Néel temperature. These results are compared with magnetovolume effects in the RCo2 compounds.