Heat capacity of CuGeO3:: Anisotropic magnetic field dependence of the uniform phase

Heat capacity measurements have been performed on high quality monocrystalline 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 vicinity of the spin-Peierls transition is field-dependent in a reversible manner up to 11 T for a field orientation parallel to the c axis, whereas no variation occurs for field orientation perpendicular to c. Such a behavior is perhaps related to the irreversible and progressive decrease of C-m under external factors such as application of intense magnetic fields or cooling cycles that we have previously reported for the same crystals of initial high structural quality. (C) 1998 Elsevier Science Ltd. All rights reserved.