Thermal expansion and specific heat of monocrystalline URu2Si2

Thermal-expansion and specific-heat measurements have been performed on a monocrystalline sample of URu2Si2 in the temperature region between 1.4 and 100 K. The thermal expansion of this tetragonal compound is strongly anisotropic and exhibits several anomalies in the investigated temperature range. Broad anomalies are centered around 5 and 25 K, whereas sharp peaks in the thermal-expansion coefficients are observed at the transition to the antiferromagnetic state at 17.5 K. The c/a ratio exhibits a similar temperature dependence as the susceptibility along the tetragonal axis. The anomaly in the thermal expansion near 25 K suggests the presence of crystal-field effects, in agreement with recent calculations for the magnetic suceptibility at elevated temperatures