Thermal relaxation in charge ordered Pr0.63Ca0.37MnO3 in the presence of a magnetic field

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 TMH<T<TCO, where TCO is the charge ordering temperature and TMH is the charge melting temperature in a field. In this temperature range, the system has coexisting charged ordered insulator (COI) and ferromagnetic metallic (FMM) phases. No such relaxation is observed in the COI state in H=0 T or in the FMM phase at T<TMH 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.