Inelastic neutron scattering study of magnetic interactions in CsMnxMg1−xBr3. I. Spin waves in CsMnBr3

Abstract

The inelastic neutron scattering technique was used to determine the dispersion of the spin-wave excitations of the triangular antiferromagnet ${\mathrm{CsMnBr}}_3$ below $T_N$=8.3 K. Two spin-wave branches of transverse and longitudinal symmetry were observed which are excellently described on the basis of a spin-wave model including an intrachain exchange coupling J=-890±10 μeV, an interchain exchange coupling J’ ’=-1.7±0.1 μeV, and a single-ion anisotropy parameter D=12±1 μeV. The small value of the ratio J’ ’/J indicates the one-dimensional magnetic character of ${\mathrm{CsMnBr}}_3$. Care has to be taken in the interpretation of the observed energy spectra with respect to two-magnon scattering contributions. Our data are consistent with the recently observed spin-wave energy gap of ${\mathrm{CsMnBr}}_3$ in the one-dimensional state.