Magnetic and thermodynamic properties of Sr_{2}LaFe_{3}O_{9}

TL;DR

This paper investigates the magnetic and thermodynamic properties of Sr_{2}LaFe_{3}O_{9} using a theoretical model, revealing a first-order magnetic transition and characterizing magnon spectra with both gapless and gapped modes.

Contribution

It introduces a Dirac-Heisenberg Hamiltonian with biquadratic exchange interactions to explain iron disproportionation effects and fits experimental data to estimate exchange integrals.

Findings

Identification of a first-order magnetic transition.

Estimation of exchange integrals consistent with similar compounds.

Magnon spectrum with one gapless and two gapped modes.

Abstract

Using a Dirac-Heisenberg Hamiltonian with biquadratic exchange interactions, we study the effect of iron disproportionation on the magnetic ordering, and describe the first-order magnetic transition occurring in the perovskite Sr_{2}LaFe_{3}O_{9}. Upon fitting the experimental data, we give an estimate of the exchange integrals for the antiferromagntic and ferromagnetic interactions, in agreement with previous works on kindered compounds. Spin-wave theory yields a magnon spectrum with a gapless antiferromagnetic mode together with two gapped ferromagnetic ones.