The effect of pressure on the magnetic susceptibility of RInCu₄ (R = Gd, Er and Yb)

The magnetic susceptibility of the intermetallic compounds RInCu₄ (R = Gd, Er and Yb) was measured under helium gas pressure up to 2 kbar at the fixed temperatures 78, 150 and 300 K. For YbInCu₄, which exhibits a first-order valence phase transition at T_V40 K, the Grüneisen parameter for the Kondo energy, _K-dlnT_K/dlnV = -32, is large and typical for Ce-based heavy-fermion systems in magnitude but opposite in sign. The effect of atomic disorder is discussed on the basis of the data for a chemically disordered sample; the pressure effect at T = 78 K is strongly enhanced due to the spatial dispersion of pressure-sensitive T_V, and hence dT_V/dP = -2.0 K kbar^-1 is obtained by assuming a Gaussian distribution of T_V. On the basis of an extrapolation of the experimental pressure dependence, a (P,T) phase diagram is proposed for YbInCu₄. Reference compounds with stable f moments, GdInCu₄ and ErInCu₄, show negligible pressure dependences of the susceptibility.