Nanoclustering phase competition induces the resistivity hump in colossal magnetoresistive manganites

TL;DR

This paper models how nanocluster phase competition causes the resistivity hump in colossal magnetoresistive manganites, revealing the microscopic coexistence of charge-ordered and ferromagnetic regions and their impact on electrical properties.

Contribution

It introduces a detailed theoretical model demonstrating the coexistence and evolution of nanoclusters in CMR manganites, explaining the resistivity hump phenomenon.

Findings

Coexistence of charge-ordered and ferromagnetic nanoclusters above T_c.

Resistivity increases as nanoclusters grow and merge with decreasing temperature.

External magnetic fields and bandwidth affect nanocluster volume fractions and resistivity.

Abstract

Using a two-band double-exchange model with Jahn-Teller lattice distortions and super-exchange interactions, supplemented by quenched disorder, at electron density $n=0.65$, we explicitly demonstrate the coexistence of the $n$ = 1/2-type ($\pi, \pi$) charge-ordered and the ferromagnetic nanoclusters above the ferromagnetic transition temperature $T_{\rm c}$ in colossal magnetoresistive (CMR) manganites. The resistivity increases due to the enhancement of the volume fraction of the charge-ordered and the ferromagnetic nanoclusters with decreasing the temperature down to $T_{\rm c}$. The ferromagnetic nanoclusters start to grow and merge, and the volume fraction of the charge-ordered nanoclusters decreases below $T_{\rm c}$, leading to the sharp drop in the resistivity. By applying a small external magnetic field $h$, we show that the resistivity above $T_{\rm c}$ increases, as compared with the case when $h=0$, a fact which further confirms the coexistence of the charge-ordered and the ferromagnetic nanoclusters. In addition, we show that the volume fraction of the charge-ordered nanoclusters decreases with increasing the bandwidth and consequently the resistivity hump diminishes for large bandwidth manganites, in good qualitative agreement with experiments. The obtained insights from our calculations provide a complete pathway to understand the phase competition in CMR manganites.