Temperature-dependent striped antiferromagnetism of LaFeAsO in a Green’s functionapproach

Abstract

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