Inhomogeneous Phases in a Double-Exchange Magnet with Long Range Coulomb Interactions

TL;DR

This paper investigates how long-range Coulomb interactions influence inhomogeneous magnetic phases in a double-exchange model, revealing preferred droplet and stripe configurations relevant for manganate thin films.

Contribution

It demonstrates that Coulomb interactions prevent macroscopic phase separation, leading to specific inhomogeneous magnetic structures in a two-dimensional double-exchange system.

Findings

Diamond-shaped ferromagnetic droplets at low densities

Diagonal stripe phases at higher densities

Relevance for manganate thin film experiments

Abstract

We consider a model with competing double-exchange (ferromagnetic) and super-exchange (anti-ferromagnetic) interactions in the regime where phase separation takes place. The presence of a long range Coulomb interaction frustrates a macroscopic phase separation, and favors microscopically inhomogeneous configurations. We use the variational Hartree-Fock approach, in conjunction with Monte-Carlo simulations to study the geometry of such configurations in a two-dimensional system. We find that an array of diamond shaped ferromagnetic droplets is the preferred configuration at low electronic densities, while alternating ferromagnetic and anti-ferromagnetic diagonal stripes emerge at higher densities. These findings are expected to be relevant for thin films of colossal magneto-resistive manganates.