Pressure effects and specific heat in superconducting HoNi2B2C

We have studied the interaction of superconductivity (Tc=8.4 K) and magnetism (TN=5 K) in the HoNi2B2C system. Specific-heat measurements at 0 and 2 T indicate that the antiferromagnetic ground state involves a Ho 4f doublet, with the entropy shifting to higher temperatures, TTN, with increasing magnetic field. The heat-capacity anomaly at Tc, ΔC/Tc, is 10 (2) mJ/mole K2, similar to the values found for other borocarbide superconductors where the density of states at the Fermi level is comprised primarily of metal d states. Magnetic susceptibility and resistivity measurements under hydrostatic pressure P reveal that dTc/dP∼0.07 (0.04) K/kbar and dTN/dP∼0.25 (0.03) up to 7 kbar. These results reveal that the structure has an important influence on the superconducting and magnetic properties of HoNi2B2C.