Competing Orders and Disorder-induced Insulator to Metal Transition in Manganites

TL;DR

This study uses Monte Carlo simulations to explore how disorder influences the competition between ferromagnetic metallic and charge-ordered insulating phases in manganites, revealing disorder-induced phase transitions and effects on magnetoresistance.

Contribution

It demonstrates how disorder suppresses charge ordering more than ferromagnetism, inducing insulator-metal transitions and affecting magnetoresistance without percolation or clustering.

Findings

Disorder favors ferromagnetic metallic phase near phase boundary.

Above Curie temperature, disorder enhances insulating behavior.

Charge/lattice fluctuations persist and grow near transition temperature.

Abstract

Effects of disorder on the two competing phases, i.e., the ferromagnetic metal and the commensurate charge/lattice ordered insulator, are studied by Monte Carlo simulation. The disorder suppresses the charge/lattice ordering more strongly than the ferromagnetic order, driving the commensurate insulator to the ferromagnetic metal near the phase boundary in the pure case. Above the ferromagnetic transition temperature, on the contrary, the disorder makes the system more insulating, which might cause an enhanced colossal magnetoresistance as observed in the half-doped or Cr-substituted manganites. No indication of the percolation or the cluster formation is found, and there remain the charge/lattice fluctuations instead which are enhanced toward the transition temperature.