The evolution with temperature of magnetic polaron state in an antiferromagnetic chain with impurities

TL;DR

This paper investigates how magnetic polarons in a one-dimensional antiferromagnetic chain with impurities evolve with temperature, revealing their stability above the Néel temperature and conditions for depinning and disappearance.

Contribution

It introduces a combined variational and Monte Carlo approach to analyze temperature effects on magnetic polarons in impurity-doped chains, highlighting their stability and depinning behavior.

Findings

Magnetic polarons remain stable above the Néel temperature.

Depinning of polarons occurs at temperatures around the Néel temperature.

Polarons disappear at high temperatures near the electron hopping integral.

Abstract

The thermal behavior of a one-dimensional antiferromagnetic chain doped by donor impurities was analyzed. The ground state of such a chain corresponds to the formation of a set of ferromagnetically correlated regions localized near impurities (bound magnetic polarons). At finite temperatures, the magnetic structure of the chain was calculated simultaneously with the wave function of a conduction electron bound by an impurity. The calculations were performed using an approximate variational method and a Monte Carlo simulation. Both these methods give similar results. The analysis of the temperature dependence of correlation functions for neighboring local spins demonstrated that the ferromagnetic correlations inside a magnetic polaron remain significant even above the N\'eel temperature $T_N$ implying rather high stability of the magnetic polaron state. In the case when the electron-impurity coupling energy $V$ is not too high (for $V$ lower that the electron hopping integral $t$), the magnetic polaron could be depinned from impurity retaining its magnetic structure. Such a depinning occurs at temperatures of the order of $T_N$. At even higher temperatures ($T \sim t$) magnetic polarons disappear and the chain becomes completely disordered.