Anomalous field-dependent specific heat in charge-ordered ${\mathrm{Pr}}_{1-x}{\mathrm{Ca}}_x{\mathrm{MnO}}_3$ and ${\mathrm{La}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{MnO}}_3$

We report low temperature specific heat measurements of ${\mathrm{Pr}}_{1-x}{\mathrm{Ca}}_x{\mathrm{MnO}}_3$ $(0.3\mathrm{}<~x<~0.5)$ and ${\mathrm{La}}_{0.5}{\mathrm{Ca}}_{0.5}{\mathrm{MnO}}_3$ with and without applied magnetic field. An excess specific heat, $C^{\prime }\mathrm{}\left(T\right),$ of nonmagnetic 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 ${\mathrm{Pr}}_{1-x}{\mathrm{Ca}}_x{\mathrm{MnO}}_3$ compounds exhibit a large contribution linear in temperature $\left(\gamma T\right)$ originating from magnetic and charge disorder.