New Critical Exponent β of the XY Antiferromagnet on Stacked Triangular Lattice, CsMnBr3

The phase transition of the XY antiferromagnet on a stacked triangular lattice, CsMnBr 3 is studied by neutron diffraction. The critical exponent β is found to be β=0.25±0.01. The value is in excellent agreement with the predicted value by Kawamura for a new universality class, giving convincing experimental support to the phase transition characterized by the Z 2 ×S 1 or O(2) symmetry.