We report low temperature specific heat measurements of Pr$_{ 1-x}$Ca$_{ x}$MnO$_{ 3}$ ($0.3\leq x \leq 0.5$) and La$_{ 0.5}$Ca$_{ 0.5}$MnO$_{ 3}$ with and without applied magnetic field. An excess specific heat, $C^{ \prime}(T)$, of non-magnetic origin associated with charge ordering is found for all the samples. A magnetic field sufficient to induce the transition from the charge-ordered state to the ferromagnetic metallic state does not completely remove the $C^{ \prime}$ contribution. This suggests that the charge ordering is not completely destroyed by a "melting" magnetic field. In addition, the specific heat of the Pr$_{ 1-x}$Ca$_{ x}$MnO$_{ 3}$ compounds exhibit a large contribution linear in temperature ($\gamma T$) originating from magnetic and charge disorder.
Categories: cond-mat.str-el