Effect of Jahn-Teller interactions on the specific heat and magnetic properties of charge-orderedLa1−xCaxMnO3(0.55⩽x⩽0.87)compounds

Abstract

The effect of Jahn-Teller (JT) interactions on specific heat and magnetic properties was studied for the series of ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}\mathrm{Mn}{\mathrm{O}}_{3}$ $(0.55\ensuremath{\leqslant}x\ensuremath{\leqslant}0.87)$ compounds by measurements of specific heat, ultrasonic velocity, and magnetization. Upon increasing $x$ from 0.55 to 0.75, the enhancement of the JT interactions suppresses the ferromagnetic fluctuation above the charge ordering (CO) transition temperature ${T}_{\mathrm{CO}}$, increases the change of entropy associated with the charge/orbital ordering transition, and therefore enhances the stability of the CO state. With further increasing $x$ from 0.75 to 0.87, the ferromagnetic fluctuation gradually swells up and the change of entropy almost linearly decreases, due to the reduction of the JT interactions. The magnetic field dependence of ${T}_{\mathrm{CO}}$ was estimated based on the Clausius-Clapeyron equation, which well coincides with that obtained from the transport measurements in high magnetic fields. These results imply that the JT effect is a key ingredient in understanding the essential physics of the CO state.