MAGNETIC PHASES OF CSCUCL3 - ANOMALOUS CRITICAL-BEHAVIOR

We report high-resolution measurements of the specific heat of the hex agonal antiferromagnet CsCuCl3 with ferromagnetically coupled Cu2+ cha ins in magnetic fields parallel to the hexagonal axis. The zero-field data can be described assuming a second-order phase transition with a chiral XY critical exponent alpha near 0.35, except very close to the Neel temperature where the transition seems to be of weakly first orde r. This might be an indication for the failure of XY chiral universali ty. The previously observed first-order transition from an ''umbrella' ' to a coplanar spin structure at high fields merges the transition li ne to the paramagnet in a multicritical point (T-c = 10.59 K, B-m = 5. 5 T). The transition to the new coplanar structure from the saturated paramagnetic phase above B-m seems, rather unexpectedly, also to be de scribable as a second-order transition with alpha approximate to 0.23.