Suppression of Ferromagnetic Double Exchange by Vibronic Phase Segregation

TL;DR

This study investigates how vibronic phase segregation suppresses ferromagnetic double exchange in manganites, providing a quantitative model that explains experimental deviations in transition temperatures and the conditions for colossal magnetoresistance.

Contribution

It introduces a mean-field model that quantitatively explains deviations in TC and predicts a first order transition due to vibronic effects in manganites.

Findings

Quantitative agreement with measured TC deviations

Prediction of a first order transition in strong coupling regime

Identification of a temperature interval where CMR may occur

Abstract

From Raman spectroscopy, magnetization, and thermal-expansion on the system La2/3(Ca1-xSrx)1/3MnO3, we have been able to provide a quantitative basis for the heterogeneous electronic model for manganites exhibiting colossal magnetoresistance (CMR). We construct a mean-field model that accounts quantitatively for the measured deviation of TC(x) from the TC predicted by de Gennes double exchange in the adiabatic approximation, and predicts the occurrence of a first order transition for a strong coupling regime, in accordance with the experiments. The existence of a temperature interval TC<T<T* where CMR may be found is discussed, in connection with the occurrence of an idealized Griffiths phase.