Collapse of the charge-ordering state at high magnetic fields in the rare-earth manganite Pr<SUB>0.63</SUB>Ca<SUB>0.37</SUB>MnO<SUB>3</SUB>

We have investigated the specific heat and resistivity of a single crystal of Pr<SUB>0.63</SUB>Ca<SUB>0.37</SUB>MnO<SUB>3</SUB> around the charge ordering (CO) transition temperature, T<SUB>CO</SUB>, in the presence of high magnetic fields (&#8804;12 T) which can melt the charge-ordered state. At low magnetic fields (&#8804;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&lt;T<SUB>CO</SUB>. However, above a critical field &#956;<SUB>0</SUB>H<SUP>&#8727;</SUP><SUB>&#961;</SUB>, the sample shows the onset of a metallic phase for T&gt;T<SUB>CO</SUB> 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 &#956;<SUB>0</SUB>H<SUP>&#8727;</SUP>, the COI transition does not occur and the CO state ceases to occur at all T. The entropy change involved in the CO transition, &#916;S<SUB>CO</SUB>&#8776;1.6 J/mol K at 0 T, decreases with increasing field and eventually vanishes for a field &#956;<SUB>0</SUB>H<SUP>&#8727;</SUP>. The collapse of the CO state above &#956;<SUB>0</SUB>H<SUP>&#8727;</SUP> is thus associated with a collapse of the entropy that stabilizes the CO state