We report the observation of substantial thermal relaxation in a single crystal of the charge ordered system Pr0.63Ca0.37MnO3 in an applied magnetic field of H = 8 T. The relaxation is observed when the temperature is scanned in the presence of a magnetic field in the temperature interval T-MH < T < T-CO, where T-CO is the charge ordering temperature and T-MH is the charge melting temperature in a field. In this temperature range, the system has coexisting charged ordered insulator (COT) and ferromagnetic metallic (FMM) phases. No such relaxation is observed in the COT state in H = 0 T or in the FMM phase at T < T-MH in the presence of a magnetic field. We conclude that the thermal relaxation is due to two coexisting phases with nearly the same free energies but separated by a potential barrier. This barrier makes the transformation from one phase to the other time-dependent in the scale of the specific heat experiment and gives rise to the thermal relaxation. (C) 2001 Elsevier Science Ltd. All rights reserved. References: 13
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