INFLUENCE OF CHIRAL SYMMETRY ON THE CRITICAL BEHAVIOR OF STACKED TRIANGULAR ANTIFERROMAGNETS

Abstract

We review and extend our recent specific-heat results of three antiferromagnetic quasi-onedimensional magnets, CsMnBr 3, CsNiCl 3, and CsMnI 3, with chiral symmetry. In zero field, CsMnBr 3 exhibits an unusually large critical specific-heat exponent α in good agreement with predictions for chiral XY symmetry. The anisotropy-crossover exponent ɸ has been determined in low fields applied perpendicular to the c axis. ɸ is clearly smaller than unity and differs from theoretical predictions. For CsNiCl 3 we find a crossover in fields B||c from conventional universality behavior for B=0 to chiral Heisenberg behavior at the multicritical point BM=2.3 T and further to chiral XY behavior at still higher fields. The critical exponents and also the amplitude ratios of the specific heat are in excellent agreement with theory. A magnetic field applied 13° off the c axis modifies the phase diagram, but the critical parameters remain essentially unchanged. Finally, specific-heat measurements of CsMnI 3 confirm the crossover for easy-axis antiferromagnets with chiral symmetry and yield an exponent α=0.28±0.06 at the multicritical point. At 7 T, we find α=0.33±0.06. These values are again in very good agreement with the predictions for the chiral Heisenberg and chiral XY universality classes.