Heat capacity and ac magnetic susceptibility measurements of magnetic superconductor HoNi₂B₂C under pressure

A magnetic superconductor HoNi₂B₂C exhibits the superconducting transition at around 8.5 K and successive antiferromagneic transitions at around 5 K. We have performed the heat capacity measurements for P ≤ 12 kbar and ac magnetic susceptibility measurements for P ≤ 23 kbar, in order to investigate the pressure dependence of these transitions. The above two kinds of transitions show contrary pressure dependence each other. At around P = 23 kbar, they cannot be distinguished each other, and this situation is similar to that in Ho_0.8Dyo₂Ni₂B₂C. The magnetic entropy (S) consumed at the magnetic transitions decreases with dS/dP = -0.14 J/K-mol-kbar suggesting that the crystalline electric field changes by applying pressure.