Double-exchange model: phase separation versus canted spins

TL;DR

This paper investigates the ground states of the double-exchange model, revealing that homogeneous canted states are unstable and tend to phase separate into antiferromagnetic and ferromagnetic regions, with implications for doped manganites.

Contribution

It demonstrates the instability of the canted state against phase separation and explores conditions leading to mixed magnetic phases in the double-exchange model.

Findings

Homogeneous canted states are unstable and tend to phase separate.

Phase separation can occur into antiferromagnetic and ferromagnetic/canted states.

Percolated states with ferromagnetic polarons are possible.

Abstract

We study the competition between different possible ground states of the double-exchange model with strong ferromagnetic exchange interaction between itinerant electrons and local spins. Both for classical and quantum treatment of the local spins the homogeneous canted state is shown to be unstable against a phase separation. The conditions for the phase separation into the mixture of the antiferromagnetic and ferromagnetic/canted states are given. We also discuss another possible realization of the phase-separated state: ferromagnetic polarons embedded into an antiferromagnetic surrounding. The general picture of a percolated state, which emerges from these considerations, is discussed and compared with results of recent experiments on doped manganaties.