Tetracritical dynamics of CsMnBr3

Neutron inelastic scattering has been used to measure the spin dynamics of the chiral antiferromagnet CsMnBr3 at the tetracritical point. Close to the magnetic zone centre, dynamical scaling is observed to hold with a critical exponent z=1.47±0.06. Further away from the ordering wavevector well-defined excitations are observed whose energies show surprisingly little renormalization relative to the low temperature spin wave energies. The lineshape of the scattering at these large wavevectors is well described by a theoretical form due to Halperin and Hohenberg.