High temperature specific heat and magnetic measurements in Nd0.5Sr0.5MnO3 and R0.5Ca0.5MnO3 (R=Nd, Sm, Dy and Ho) samples

TL;DR

This study investigates the specific heat and magnetic properties of various Nd, Sm, Dy, and Ho manganese oxide samples, revealing phase transitions, phonon behavior, and entropy changes with minimal magnetic field influence.

Contribution

It provides detailed specific heat measurements under magnetic fields and fits high-temperature data with an Einstein phonon model, enhancing understanding of phase transitions in these materials.

Findings

Charge ordering and ferromagnetic transition peaks observed in specific heat.

Entropy change is greater for charge ordering than ferromagnetic transition.

Magnetic field has little effect on the specific heat of the charge ordering phase.

Abstract

We have made a magnetic characterization of Nd0.5Sr0.5MnO3, Nd0.5Ca0.5MnO3, Sm0.5Ca0.5MnO3, Dy0.5Ca0.5MnO3 and Ho0.5Ca0.5MnO3 polycrystalline samples. Ferromagnetic, antiferromagnetic and charge ordering transitions in our samples agree with previous reports. We also report specific heat measurements with applied magnetic fields between 0 and 9 T and temperatures between 2 and 300 K in all cases. Each curve was successfully fitted at high temperatures by an Einstein model with three optical phonon modes. Close to the charge ordering and ferromagnetic transition temperatures the specific heat curves showed peaks superposed to the characteristic response of the lattice oscillations. The entropy variation corresponding to the charge ordering transition was higher than the one corresponding to the ferromagnetic transition. The external magnetic field seems to have no effect in specific heat of the CO phase transition.