Magnetic phase transitions in heavy-fermion compounds studied by thermal-expansion measurements

On alloying the heavy-fermion compounds CeRu2Si2 and UPt3 with small amounts of La and Pd, respectively, long-range antiferromagnetic order develops with Neel temperatures in the order of a few kelvin. In order to study the volume effects that are involved with the evolution into the long-range ordered state, we have performed thermal-expansion measurements on the pure and doped systems. The results are compared with data on antiferromagnetic URu2Si2. Subsequently, we discuss thermal-expansion measurements in high-magnetic fields, in particular on CeRu2Si2, where a metamagnetic-like transition occurs as the intersite-correlations collapse in a field of 7.8 T. Most of the measurements have been performed on single-crystalline samples, revealing a pronounced anisotropy. (orig.)