Instabilities and Insulator-Metal transitions in Half-Doped Manganites induced by Magnetic-Field and Doping

TL;DR

This paper investigates the phase diagram of half-doped manganites, focusing on how magnetic fields and doping induce phase transitions, including insulator-metal transitions, through competing interactions and instabilities.

Contribution

It provides a self-consistent analysis of Jahn-Teller distortions, charge, orbital, and magnetic orders, revealing the mechanisms behind phase instabilities and transitions in manganites.

Findings

CE phase undergoes a first-order transition to ferromagnetic metal under magnetic field.

Particle-hole asymmetry influences spin canting and carrier mobility.

Transition fields are small and governed by competing interactions.

Abstract

We discuss the phase diagram of the two-orbital model of half-doped manganites by calculating self-consistently the Jahn-Teller (JT) distortion patterns, charge, orbital and magnetic order at zero temperature. We analyse the instabilities of these phases caused by electron or hole doping away from half-doping, or by the application of a magnetic-field. For the CE insulating phase of half-doped manganites, in the intermediate JT coupling regime, we show that there is a competition between canting of spins (which promotes mobile carriers) and polaronic self-trapping of carriers by JT defects. This results in a marked particle-hole asymmetry, with canting winning only on the electron doped side of half-doping. We also show that the CE phase undergoes a first-order transition to a ferromagnetic metallic phase when a magnetic-field is applied, with abrupt changes in the lattice distortion patterns. We discuss the factors that govern the intriguingly small scale of the transition fields. We argue that the ferromagnetic metallic phases involved have two types of charge carriers, localised and band-like, leading to an effective two-fluid model.