Heat Capacity and Ac Magnetic Susceptibility Measurements of Magnetic Superconductor HoNi2B2C under Pressure

A magnetic superconductor HoNi 2 B 2 C 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 0.8 Dy 0.2 Ni 2 B 2 C. The magnetic entropy ( S ) consumed at the magnetic transitions decreases with d S /d P = -0.14 J/K·mol·kbar suggesting that the crystalline electric field changes by applying pressure.