Chiral critical behaviour in CsNiCl3

Neutron diffraction experiments have been performed on the hexagonal antiferromagnet CsNiCl3 in order to determine the critical exponent beta along the phase boundary between paramagnetic and spin-flop phase. At field strengths far above the spin-flop field our data are consistent with predictions for the n = 2 chiral universality class, beta = 0.25. Close to the spin-flop transition, where the weak Ising anisotropy present in CsNiCl3 is cancelled by the magnetic field, good agreement is achieved with the critical exponent of the n = 3 chiral universality class.