Collapse of the charge-ordering state at high magnetic fields in the rare-earth manganite Pr_0.63Ca_0.37MnO₃

Abstract

We have investigated the specific heat and resistivity of a single crystal of Pr_0.63Ca_0.37MnO₃ around the charge ordering (CO) transition temperature, T_CO, in the presence of high magnetic fields (≤12 T) which can melt the charge-ordered state. At low magnetic fields (≤10 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 μ₀H^∗_ρ, 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 μ₀H^∗, the COI transition does not occur and the CO state ceases to occur at all T. The entropy change involved in the CO transition, ΔS_CO≈1.6 J/mol K at 0 T, decreases with increasing field and eventually vanishes for a field μ₀H^∗. The collapse of the CO state above μ₀H^∗ is thus associated with a collapse of the entropy that stabilizes the CO state.