Critical features of colossal magnetoresistive manganites

TLDR

Colossal magnetoresistance in perovskite manganites arises from competition between a double‑exchange ferromagnetic metal and a charge–orbital ordered antiferromagnetic phase, with quenched disorder and phase separation near a bicritical point altering the electronic phase diagram. The study aims to demonstrate that external magnetic fields effectively suppress phase fluctuations, establishing this suppression as the key element of CMR physics. This suppression is achieved through unconventional phase control of the competing phases by magnetic, electric, and photo‑excitation fields, illustrated with numerous material‑system examples.

Abstract

Colossal magnetoresistance (CMR) phenomena are observed in the perovskite-type hole-doped manganites in which the double-exchange ferromagnetic metal phase and the charge–orbital ordered antiferromagnetic phase compete with each other. The quenched disorder arising from the inherent chemical randomness or the intentional impurity doping may cause major modifications in the electronic phase diagram as well as in the magnetoelectronic properties near the bicritical point that is formed by such a competition of the two phases. One is the phase separation phenomenon on various time-scales (from static to dynamic) and on various length-scales (from glass-like nano to grain-like micron). The other is the enhanced phase fluctuation with anomalous reduction in the transition temperatures of the competing phases (and hence in the bicritical-point temperature). The highly effective suppression of such a phase fluctuation by an external magnetic field is assigned here to the most essential ingredient of the CMR physics. Such profound and dramatic features as appearing in the bicritical region are extensively discussed in this paper with ample examples of the material systems specially designed for this purpose. The unconventional phase-controls over the competing phases in terms of magnetic/electric fields and photo-excitations are also exemplified.