抄録
Universality classes of successive magnetic phase transitions in the triangular lattice antiferromagnet CsMnI3 are studied by measuring the critical exponents γ and ν using neutron scattering. The critical exponents of the successive transitions at TN1=11.2 K and TN2=8.2 K, which correspond to orderings of magnetic moments parallel and perpendicular to the c-axis, respectively, are determined to be γ⁄⁄=1.12±0.07, ν⁄⁄=0.59±0.03 (TN1) and γ⊥=1.04±0.03, ν⊥=0.56±0.02 (TN2). These values and the β exponents β⁄⁄=0.32±0.01, β⊥=0.35±0.01 measured in our previous work do not agree with a theory which predicted the three dimensional XY universality for both the transitions. This is in contrast with the satisfactory agreement of critical exponents of CsMnBr3 with a theory of the novel three-dimensional Z2×S1 universality. A uniform magnetization parallel to the c-axis in terms of the three sublattices in the c-plane is found to increase slowly below TN1.
