We report low temperature specific heat measurements of
Pr1−xCaxMnO3 (0.3≤x≤0.5) and
La0.5Ca0.5MnO3 with and without applied magnetic field. An
excess specific heat, C′(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′ contribution. This
suggests that the charge ordering is not completely destroyed by a "melting"
magnetic field. In addition, the specific heat of the
Pr1−xCaxMnO3 compounds exhibit a large contribution linear in
temperature (γT) originating from magnetic and charge disorder.Comment: submitted to PRL 5 pages, 3 figures include