Jahn-Teller effect and stability of the charge-ordered state in La1-xCaxMnO3 (0.5<x<0.9) manganites

TL;DR

This study investigates how the Jahn-Teller effect influences the stability of charge-ordered states in La1-xCaxMnO3 manganites, revealing a maximum in electron-lattice interaction strength at x=0.75 and its insensitivity to magnetic fields.

Contribution

It provides detailed experimental evidence linking Jahn-Teller distortions to charge ordering stability across different calcium concentrations.

Findings

Maximum sound velocity change at x=0.75 indicating strongest Jahn-Teller effect

Charge-ordered state stability is highest near x=0.75 and unaffected by magnetic fields

Lattice parameter changes correlate with charge ordering transition temperature

Abstract

The longitudinal ultrasonic sound velocity and attenuation, the resistivity, and lattice parameters were studied as a function of temperature from 30 K to 300 K in La1-xCaxMnO3 (0.5<x<0.9). For all the samples, a dramatic stiffening of the sound velocity below the charge ordering transition temperature TCO was directly driven by distinct changes of the lattice parameters due to the formation of long range ordering of Jahn-Teller distorted MnO6 octahedra. The relative change of the sound velocity (DeltaV/V) below TCO depends on the Ca concentration x and reaches the maximum at x=0.75, implying that the effective strength of electron-lattice interaction with the Jahn-Teller distortion is the strongest at x=0.75 and hence the charge ordered state is mostly stabilized near x=0.75 and insensitive to the application of a magnetic field, which is supported by the charge transport properties under high magnetic fields up to 14T.