The single-ion anisotropy in LaFeAsO

TL;DR

This paper uses Green's function methods to analyze the magnetic properties of LaFeAsO, focusing on the effects of single-ion anisotropy and inter-layer coupling on the transition temperature and spin spectrum gap.

Contribution

It provides analytical expressions for $T_N$ and $ riangle$, and discusses the impact of single-ion anisotropy $J_s$ on magnetic properties of LaFeAsO.

Findings

$J_s$ and $J_c$ magnitudes can compete.

Both $T_N$ and spin gap increase with $J_s$.

Calculated spin gap at low temperature aids future experiments.

Abstract

We use Green's function method to study the Heisenberg model of LaFeAsO with the striped antiferromagnetic collinear spin structure. In addition to the intra-layer spin couplings $J_{1a},J_{1b},J_2$ and the inter-layer coupling $J_c$, we further consider the contributions of the single-ion anisotropy $J_s$. The analytical expressions for the magnetic phase-transition temperature $T_N$ and the spin spectrum gap $\Delta$ are obtained. According to the experimental temperature $T_N=138$K and the previous estimations of the coupling interactions, we make a further discussion about the magnitude and the effects of the single-ion anisotropy $J_s$. We find that the magnitudes of $J_s$ and $J_c$ can compete. The dependences of the transition temperature $T_N$, the zero-temperature average spin and the spin spectrum gap on the single-ion anisotropy are investigated. We find they both increase as $J_s$ increases. The spin spectrum gap at low temperature $T\to0$ is calculated as a function of $J_s$, the result of which is a useful reference for the future experimental researches.