Influence of charge ordering on the magnetocaloric effect of (Pr,Ca)MnO$_3$ manganites

TL;DR

This study investigates how charge ordering affects the magnetocaloric effect in Pr-Ca manganites, revealing an anomalous entropy change linked to charge and spin ordering, and demonstrating colossal effects near the insulator-metal transition.

Contribution

It provides new insights into the interplay between charge ordering and magnetocaloric properties, highlighting the colossal effect near the irreversibility temperature in CMR manganites.

Findings

Charge ordering influences the magnetic entropy change below T_CO.

Anomalous positive entropy contribution due to charge ordering observed.

Colossal magnetocaloric effect occurs near T* in CMR manganites.

Abstract

In the present work we analyze the influence of the charge-ordering on the magnetocaloric effect of Pr$_{1-x}$Ca$_x$MnO$_3$ manganites. The results for the samples with $x<$0.30 present the usual ferromagnetic behavior, peaking at the Curie temperature T$_C$. In contrast, for the samples above the onset concentration for the charge-ordering ($x\sim$0.30), an anomalous magnetic entropy change was observed below the charge-ordering temperature $T_{CO}$, persisting for lower temperatures. This effect is associated to a positive contribution to the magnetic entropy change due to charge-ordering, which is superimposed to the negative contribution from the spin ordering. We found that the charge-ordering component peaks at $T_N$ and is negligible above $T_{CO}$. Moreover, around T$^\star$ (temperature below which the insulator-metal transition induced by magnetic field becomes completely irreversible, where the system remains in such state even after the external magnetic field has been removed), we found extremely large values for the magnetic entropy change, establishing a `colossal' magnetocaloric effect on CMR manganites.