THE DISORDERED MAGNETIC-STRUCTURE IN THE TRIANGULAR-LATTICE XY-ANTIFERROMAGNET CSMNBR3 DERIVED FROM THE ZERO-FIELD SPECTRUM OF BR NUCLEAR-MAGNETIC-RESONANCE

The Pr NMR in the triangular-lattice antiferromagnetic CsMnBr3 is inve stigated in the ordered state at low temperatures. Two distinct peaks of the Pr NMR spin-echo spectrum were observed at 36.0+/-0.5 MHz and 4 3.0+/-0.5 MHz accompanied by a broad signal ranging from 34 to 55 MHz in zero field. The peak frequencies are independent of temperature and the ratio of the frequencies is the same as that of the quadrupole mo ments of Br-81 and Br-79. This suggests that the quadrupole resonance of Br is perturbed by the distribution of the internal magnetic field. Theoretical results obtained under the assumption that the Mn spins h ave disordered structure in the c-plane due to the frustration effect agree with the experimental data.