Low-temperature thermal and high-pressure studies of CePd and CeAgSb₂

The anomalous properties of the Kondo lattice CeAgSb₂ are compared with the well behaved Kondo system, CePd. The low-temperature thermal expansion of CePd is in agreement with previous heat capacity data, showing a ferromagnetic transition at T_c = 6.5 K and a second transition at 3.5 K probably due to reorientation of the magnetic moments. The Grüneisen factor, calculated from thermal-expansion and heat capacity is γ_G ≈ 4.5, the same as the Grüneisen factor γ_p calculated from the pressure dependence and comparable to a previous measurement of γ_p ≈ 6. Thermal expansion measurements (in fields of up to 8 T) and ac susceptibility measurements (under pressures of up to 7.33 kbar) have been made on CeAgSb₂ in the temperature range 1.6-40 K. The zero-pressure ac susceptibility measurements confirm that there is an antiferromagnetic transition at T_N = 9.5 K, as previously reported. The magnetic contribution to the linear thermal-expansion coefficient of polycrystalline CeAgSb₂ (α_p) in zero magnetic field has a maximum value near 17 K and becomes small by 29 K. There is no peak in α_p at the Néel temperature. The Néel temperature is found to decrease under pressure at the rate of ∂(lnT_N)/∂P = -10.1 Mbar^-1, which indicates that CeAgSb₂ is a magnetic Kondo lattice (with T_K > T_N) on the right-hand side of the Doniach diagram.