Temperature-dependent striped antiferromagnetism of LaFeAsO in a Green's function approach

TL;DR

This paper employs a Green's function approach to analyze the temperature-dependent magnetic properties of LaFeAsO, providing analytical expressions for transition temperature and magnetic moments, aligning well with experimental data.

Contribution

It introduces a Green's function method to study magnetic phase transitions in LaFeAsO, including inter-layer couplings and AFM fluctuations, offering new analytical insights.

Findings

Transition temperature TN estimated at 138 K

Non-zero inter-layer AFM coupling is crucial for TN

AFM fluctuations lower the magnetic moment towards experimental values

Abstract

We use a Green's function method to study the temperature-dependent average moment and magnetic phase-transition temperature of the striped antiferromagnetism of LaFeAsO, and other similar compounds, as the parents of FeAs-based superconductors. We consider the nearest and the next-nearest couplings in the FeAs layer, and the nearest coupling for inter-layer spin interaction. The dependence of the transition temperature TN and the zero-temperature average spin on the interaction constants is investigated. We obtain an analytical expression for TN and determine our temperature-dependent average spin from zero temperature to TN in terms of unified self-consistent equations. For LaFeAsO, we obtain a reasonable estimation of the coupling interactions with the experimental transition temperature TN = 138 K. Our results also show that a non-zero antiferromagnetic (AFM) inter-layer coupling is essential for the existence of a non-zero TN, and the many-body AFM fluctuations reduce substantially the low-temperature magnetic moment per Fe towards the experimental value. Our Green's function approach can be used for other FeAs-based parent compounds and these results should be useful to understand the physical properties of FeAs-based superconductors.