Pressure effects and specific heat in superconductingHoNi2B2C

We have studied the interaction of superconductivity (${\mathit{T}}_{\mathit{c}}$=8.4 K) and magnetism (${\mathit{T}}_{\mathit{N}}$=5 K) in the ${\mathrm{HoNi}}_2$ ${\mathrm{B}}_2$C 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, T≫${\mathit{T}}_{\mathit{N}}$, with increasing magnetic field. The heat-capacity anomaly at ${\mathit{T}}_{\mathit{c}}$, ΔC/${\mathit{T}}_{\mathit{c}}$, is 10 (2) mJ/mole ${\mathrm{K}}^2$, 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 ${\mathit{dT}}_{\mathit{c}}$/dP∼0.07 (0.04) K/kbar and ${\mathit{dT}}_{\mathit{N}}$/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 ${\mathrm{HoNi}}_2$ ${\mathrm{B}}_2$C.