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

Abstract

We report low temperature specific heat measurements of Pr${}_{1-x}$Ca${}_x$MnO${}_3$ ($0.3\le x\le 0.5$) 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.

submitted to PRL 5 pages, 3 figures included