Collapse of the charge ordering state at high magnetic fields in the rare-earth manganite, Pr_{0.63}Ca_{0.37}MnO_3

Abstract

We have investigated the specific heat and resistivity of a single crystal of Pr_{0.63}Ca_{0.37}MnO_3 around the charge ordering (CO) transition temperature, T_{CO}, in the presence of high magnetic fields (<=12T) which can melt the charge ordered state. At low magnetic fields (<=10T), 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_0H_{\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_0H^*, the COI transition does not occur and the CO state ceases to occur at all T. The entropy change involved in the CO transition, \Delta S_{CO}~1.6J/molK at 0T, decreases with increasing field and eventually vanishes for a field \mu_0H^*. The collapse of the CO state above \mu_0$H$^* is thus associated with a collapse of the entropy that stabilizes the CO state.