BR-81-NMR IN THE TRIANGULAR-LATTICE XY ANTIFERROMAGNETIC CSMNBR3 BELOW 1 K

The Br-81-NMR of the triangular-lattice XY antiferromagnetic CsMnBr3 i s measured below 1.0 K. As temperature decreases starting from 350 mK, the spectrum splits up into several peaks: five sharp peaks are obser ved at 90 mK. The spin-lattice relaxation rate, 1/T-1, decreases as a function of the temperature between 1.0 K and 300 mK, and then increas es rapidly below 300 mK. These results suggest that a phase transition occurs below 300 mK.