Multiferroic phase transitions of triangular-lattice-antiferromagnet RbCoBr3

An intensive study of dielectric and magnetic properties in RbCoBr3 was performed to confirm the previously observed simultaneous onset of ferroelectric and antiferromagnetic orderings just at the antiferromagnetic transition point. The real part of the dielectric constant as a function of temperature exhibits an inflection point at 37.2 K and two anomalous round and sharp peaks at 32 K and 9.0 K, respectively. The pyroelectric charge measurement shows an anomaly at about 9.0 K, and confirmed the presence of a reversible spontaneous polarization. From the impurity effect of non-magnetic Mg2+ on the magnetic susceptibility and the dielectric constant, the Neel temperature was found to be reduced in accordance with a lowering of the ferroelectric phase transition point. Moreover, the broad peak around 32 K of the pure sample splits into two sharp peaks through the impurity doping.