Pressure-induced stabilization of an intermediate phase in the triangular lattice antiferromagnet CsNiCl3

Pressure effects on the magnetic properties of the triangular lattice Heisenberg antiferromagnet CsNiCl3 have been studied through heat capacity measurements up to the pressure of 6.6 kbar. With increasing pressure, two successive phase transitions at T-N1 = 4.74 K and T-N2 = 4.24 K at 0 kbar, which result from a small Ising-type anisotropy of S = 1 moments on Ni2+ ions, shift to higher temperatures in proportion to the pressure. Moreover, the pressure dependence of the entropy indicates that the intermediate phase AF(1) (T-N2 < T < T-N1) is stabilized. These results suggest that the pressurization enhances the Ising-type anisotropy in the spin moments.