MAGNETIC PHASE-TRANSITIONS IN CSCOBR3

Elastic neutron-scattering measurements have been performed on CsCoBr3, an Ising-like antiferromagnet on a stacked triangular lattice. Three magnetic phase transitions are seen in both zero field and a magnetic field of 2.2 T applied along the stacking direction c. The field does not qualitatively change the behavior near the phase transitions and the transition temperatures are affected only slightly. The high-temperature ordered phase is known to be partially paramagnetic and the transition from the completely paramagnetic phase to this ordered phase was carefully studied. The transition is found to be continuous and characterized by the critical exponent beta = 0.22 +/- 0.01, a result that disagrees with previous measurement. The disagreement can be attributed to a large amount of temperature-dependent paramagnetic scattering that exists in both paramagnetic and the partially paramagnetic ordered phase.