Dielectric anomaly involving magnetic phase transition in a hexagonal antiferromagnet RbCoBr3

The dielectric and magnetic phase transitions in a triangular lattice antif erromagnet RbCoBr3 were studied by means of some dielectric, magnetic and c alorimetric measurements. In this compound, which is a typical Ising-like a ntiferromagnet with antiferromagnetic moment along the hexagonal c-axis, a ferroelectric phase transition involving magnetic ordering with week ferrom agnetic moments confined in the c-plane was found to occur at T-N(=37.0K). Those results imply that the magnetic ordering of this system is assisted b y a polar lattice distortion, which can release partially the spin frustrat ion due to the antiferromagnetic spin arrangement on a triangular lattice. This co-ordering is certainly ascribed to a probable competition between la ttice-system and spin-system. Experimental data on this interesting phenome non are presented and a possible mechanism is proposed.