Neutron scattering measurements of critical exponents in CsMnBr3: A Z2≥1 antiferromagnet

Abstract

${\mathrm{CsMnBr}}_3$ is an XY-like antiferromagnet on a stacked, triangular lattice with nearest-neighbor interactions. It orders antiferromagnetically at $T_N$=8.3 K. We have used neutron scattering measurements of the frequency-integrated critical scattering in the paramagnetic state and magnetic Bragg peak intensity in the ordered state to determine the critical exponents γ, ν, and β. Based on these measurements we conclude that γ=1.01±0.08, ν=0.54±0.03, and β=0.21±0.02. These values do not correspond to any standard universality class characterized by the dimensionality of the lattice and the order parameter. They do, however, agree with predictions by Kawamura for a universality class characterized by the symmetry of the order parameter, $Z_2$×$S_1$. This symmetry differs from that of the standard XY model ($S_1$) due to the presence of chiral degeneracy ($Z_2$), a consequence of lattice frustration.