Ferromagnetic Polarons, Phase Separation, Stripes and Polaron Lattice: The two- and three-dimensional ferromagnetic Kondo Model

TL;DR

This study uses Monte Carlo simulations to explore the phase behavior of the ferromagnetic Kondo lattice model in two and three dimensions, revealing conditions for polaron stability, phase separation, and stripe formation.

Contribution

It provides the first detailed phase diagram for the 2D model and demonstrates the formation of a polaron lattice in 3D at higher doping levels.

Findings

J' > 0.02 stabilizes individual polarons in 2D.

Small J' < 0.02 favors phase separation in 2D.

3D systems form a polaron lattice without phase separation.

Abstract

We investigate the two- and three-dimensional ferromagnetic Kondo lattice model by unbiased Monte Carlo simulations. A phase diagram for the two-dimensional model is presented, in which the stability of magnetic order and ferromagnetic polarons is examined with respect to the antiferromagnetic superexchange J' and temperature. The Monte Carlo simulations reveal that J' > 0.02 strengthens individual polarons while small J' < 0.02 favors larger clusters and phase separation except for small doping. Lowering the temperature stabilizes ferromagnetic polarons for realistic J' > 0.01, while phase separation is only favored for very small J' < 0.01. Our Monte Carlo simulations show that low temperatures can lead to diagonal or vertical stripes depending on J'. Simulations for three-dimensional systems yield ferromagnetic polarons, which form a `polaron lattice' at higher doping levels 0.2 < x < 0.23, when independent polarons do no longer fit into the system. No tendency to phase separation is observed in three dimensions.