Pressure Effects on Phase Transitions in Several Hexagonal Antiferromagnets of ABX_3 Type(Impurity and Pressure Effects, Field-Induced Phase Transitions and Dynamics in Quantum Spin Systems)

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Magnetic measurements under high pressures have been performed on the hexagonal ABX_3 type antiferromagnets, CsFeCl_3, CsNiCl_3 and RbNiCl_3 to investigate the pressure effect on the magnetic phase transitions. CsFeCl_3 has the singlet ground state due to the large single-ion anisotropy of the easy-plane type at ambient pressure. Above the critical pressure Pc≃0.9GPa, CsFeCl_3 exhibits the long range magnetic ordering at zero field as the result of the collapse of the energy gap between the singlet state and the lowest excited doublet. CsNiCl_3 and RbNiCl_3 having the easy-axis type magnetic anisotropy undergo the successive phase transitions in the temperature variations and exhibit the spin-flop phase transition in the field parallel to the c-axis. With increasing pressure, the temperature range of the collinear intermediate phase and the spin-flop field H_<SF> are enhanced. This fact indicates that the easy-axis anisotropies of CsNiCl_3 and RbNiCl_3 are enhanced by the pressure as compared with the increase of the intra- and inter-chain interactions.
理論物理学刊行会の論文
2005-10-31