Thermal expansion of single-crystalline HoNi2B2C

The thermal expansion α has been measured for single-crystalline HoNi2B2C in the range between 2 and 200K. At low temperatures, α is dominated by magnetic contributions leading to a strongly anisotropic behaviour with different signs for the expansion coefficients near the antiferromagnetic phase transition. Analysing the magnetic and lattice contributions of α well above this temperature, a nearly isotropic behaviour of the latter one can be deduced. Using the Ehrenfest relation, a relatively weak pressure dependence of the superconducting transition temperature of dTc/dp=0.1K/GPa was determined for pressure applied along the c direction which points to a rather small pressure-induced lattice stiffening. The ratio between expansion coefficient and specific-heat features large values at the onset of magnetic order.