Possibilities of polarised neutrons in studies of chiral criticality are discussed. The critical exponents beta (C),. of the average chirality below T-N, as well as phi (C) = beta (C) + gamma (C) and, therefore, gamma (C) of the chiral susceptibility above T-N are determined for a XY triangular lattice antiferromagnet (TLA) CsMnBr3: beta (C) = 0.44(2), gamma (C) = 0.84(7). The critical behaviour of the chirality that orders at T, with a relative precision of 5 x 10(-4) proves that the phase transition belongs to a new chiral universality class. For the TLA CsNiCl3 (S = 1) we found in the XY region (B = 3 T) phi (C) = 1.24(7) in agreement with the Monte-Carlo value phi (C) = 1.22(6) for the chiral universality class. In the easy-axis region at B = 1 T, phi (C) = 0.54(4), and the Haldane excitations are observed in the polarisation-dependent inelastic cross section above T,. The helimagnet holmium exhibits a different chiral criticality with phi (C) = 1.56(5), essentially higher than for TLAs. (C) 2001 Elsevier Science B.V. All rights reserved. [References: 26]
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