Multi-scale Phase Modulations in Colossal Magnetoresistance Manganites

TL;DR

This paper presents extensive experimental evidence of multi-scale phase inhomogeneities in colossal magnetoresistance manganites, highlighting their role in transport phenomena and the CMR effect across different temperature regimes.

Contribution

It provides detailed experimental data on phase coexistence and nanoscale correlations, revealing their influence on magnetoresistance and metal-insulator transitions in manganites.

Findings

Micrometer-scale phase coexistence influences percolative transport.

Nanoscale charge/orbital correlations are common and crucial for CMR.

Phase inhomogeneities are governed by electron correlations and strain effects.

Abstract

Extensive experimental results are presented on the multi-scale phase modulation phenomena observed in colossal magnetoresistance manganites. Two key types of phase inhomogeneities directly relevant to the colossal magnetoresistance (CMR) are discussed. The first type involves micrometer-scale coexistence of structurally and electronically different phases. We present extensive experimental data for a prototypical system exhibiting such a phase coexistence, (La,Pr)$_{5/8}$Ca$_{3/8}$MnO$_{3}$. These data reveal that percolative transport phenomena play the key role in the metal-insulator transition in this system, and are largely responsible for the significant magnitude of the magnetoresistance. The phase composition of the multiphase states is governed by both the electron correlations and the effects of martensitic accommodation strain. The second type of an inhomogeneous state is realized in the paramagnetic state commonly found in manganites at high-temperatures. In this state, nanometer-scale structural correlations associated with nanoscale charge/orbital ordered regions are observed. Experimental investigation of numerous manganite systems indicates that these correlations are generic in orthorhombic mixed-valent manganites, and that the correlated regions play an essential role in the CMR effect.