Temperature dependence of surface magnetization in local-moment systems

TL;DR

This paper develops a theoretical model to analyze how surface magnetization in ferromagnetic semi-infinite crystals varies with temperature, highlighting the influence of surface coupling on magnetic properties and spin polarization.

Contribution

It introduces a single-site approximation combined with a localized perturbation method to study surface states' temperature dependence in local-moment systems.

Findings

Surface magnetic properties can significantly differ from bulk properties.

Higher surface and interlayer exchange coupling enhances surface Curie temperature.

Surface spin polarization is strongly affected by the coupling constants.

Abstract

We present a theory to study the temperature-dependent behavior of surface states in a ferromagnetic semi-infinite crystal. Our approach is based on the single-site approximation for the \emph{s-f} model. The effect of the semi-infinite nature of the crystal is taken into account by a localized perturbation method. Using the mean-field theory for the layer-dependent magnetization, the local density of states and the electron-spin polarization are investigated at different temperatures for ordinary and surface transition cases. The results show that the surface magnetic properties may differ strongly from those in the bulk and the coupling constant of atoms plays a decisive role in the degree of spin polarization. In particular, for the case in which the exchange coupling constant on the surface and between atoms in the first and second layer is higher than the corresponding in the bulk, an enhancement of surface Curie temperature and hence the spin polarization can be obtained.