Abstract:
We have investigated the specific heat and resistivity of a single crystal of Pr0.63Ca0.37MnO3 around the charge ordering (CO) transition temperature, T-CO, in the presence of high magnetic fields (less than or equal to12 T) which can melt the charge-ordered state. At low magnetic fields (less than or equal to10 T), the manganite transforms from a charge-disordered paramagnetic insulating (PI) state to a charge-ordered insulating (COI) state as the temperature is lowered. The COI state becomes unstable beyond a threshold magnetic field and melts to a ferromagnetic metallic phase (FMM). This occurs for T<T-CO. However, above a critical field mu(0)H(rho)(*), the sample shows the onset of a metallic phase for T>T-CO and the COI transition occurs from a metallic phase. The onset temperature of the high-field metallic behavior decreases with an increase in the field and above a field mu(0)H(*), the COI transition does not occur and the CO state ceases to occur at all T. The entropy change involved in the CO transition, DeltaS(CO)approximate to1.6 J/mol K at 0 T, decreases with increasing field and eventually vanishes for a field mu(0)H(*). The collapse of the CO state above mu(0)H(*) is thus associated with a collapse of the entropy that stabilizes the CO state.
