HEAT-CAPACITY OF CUGEO3 - ANISOTROPIC MAGNETIC-FIELD DEPENDENCE OF THE UNIFORM PHASE

Heat capacity measurements have been performed on high quality monocry stalline samples of CuGeO3 in magnetic fields up to 21 T. The magnetic contribution C-m to the heat capacity of the uniform phase in the vic inity of the spin-Peierls transition is field-dependent in a reversibl e manner up to 11 T for a field orientation parallel to the c axis, wh ereas no variation occurs for field orientation perpendicular to c. Su ch a behavior is perhaps related to the irreversible and progressive d ecrease of C-m under external factors such as application of intense m agnetic fields or cooling cycles that we have previously reported for the same crystals of initial high structural quality. (C) 1998 Elsevie r Science Ltd. All rights reserved.