Spiral magnetic phases on the Kondo Lattice Model: A Hartree-Fock approach

TL;DR

This paper investigates spiral magnetic phases in the Kondo Lattice Model on a square lattice using a Hartree-Fock approximation, revealing complex phase diagrams with temperature-dependent magnetic wavevectors.

Contribution

It introduces a semi-classical Hartree-Fock approach to map out spiral magnetic phases and their evolution with temperature in the Kondo Lattice Model.

Findings

Spiral magnetic phases interpolate between ferromagnetic and antiferromagnetic states.

Temperature can induce continuous or abrupt changes in magnetic wavevector.

Coexistence of magnetic order with Kondo screening occurs in certain parameter regions.

Abstract

We study the Kondo Lattice Model (KLM) on a square lattice through a Hartree-Fock approximation in which the local spins are treated semi-classically, in the sense that their average values are modulated by a magnetic wavevector $\mathbf{Q}$ while they couple with the conduction electrons through fermion operators. In this way, we obtain a ground state phase diagram in which spiral magnetic phases (in which the wavevector depends on the coupling constants and on the density) interpolate between the low-density ferromagnetic phase and the antiferromagnetic phase at half filling; within small regions of the phase diagram commensurate magnetic phases can coexist with Kondo screening. We have also obtained `Doniach-like' diagrams, showing the effect of temperature on the ground state phases, and established that for some ranges of the model parameters (the exchange coupling and conduction electron density) the magnetic wavevector changes with temperature, either continuously or abruptly (e.g., from spiral to ferromagnetic).