We report on high-resolution specific-heat and magnetocaloric-effect measurements of the triangular-lattice antiferromagnets $\mathrm{CsMn}({\mathrm{Br}}_x{\mathrm{I}}_{1-x}{)}_3$ with different x. The evolution of the magnetic phase diagrams from the easy-axis system for $x=0\mathrm{}$ to the easy-plane system for $x=1\mathrm{}$ was studied in detail. The specific-heat critical exponent $\alpha$ of the almost isotropic $x=0.19\mathrm{}$ system agrees with the value predicted for a chiral Heisenberg scenario. In an applied magnetic field $(B=6\mathrm{}\hspace{0.5em}\mathrm{T})$ a crossover to a weak first-order transition is detected.

• Received 1 March 2001

DOI:https://doi.org/10.1103/PhysRevB.64.094406