Spin waves in the triangular antiferromagnet CsMnBr3

We report neutron scattering measurements of the spin-wave dispersion relations in the hexagonal triangular antiferromagnet CsMnBr3. The data in the easy plane are described satisfactorily in terms of a model with Heisenberg exchange parameter J2=−0.0019 ±0.0002 meV between a magnetic atom and its six nearest neighbors and a single-ion anisotropy parameter D=0.014±0.002 meV. In a magnetic field of 3.7 T along a 〈100〉 direction the variation of the staggered magnetization, measured at (1/3 1/3 1), as a function of temperature shows two critical phase transitions separated by about 1.7 K. The triangular antiferromagnetic phase that occurs below 8.6 K in zero field is split by the field into two phases with transitions at 8.9 and 7.2 K. The intermediate phase below 8.9 K is of an unknown nature.