Magnetic interactions in EuTe epitaxial layers and EuTe/PbTe superlattices

TL;DR

This study investigates the magnetic properties of EuTe epitaxial layers and EuTe/PbTe superlattices, revealing how layer thickness, strain, and interlayer interactions influence antiferromagnetic behavior using experimental and theoretical approaches.

Contribution

The paper introduces a mean field model incorporating strain effects and a tight-binding framework to explain interlayer magnetic correlations in EuTe/PbTe superlattices.

Findings

Néel temperature varies with EuTe layer thickness and strain.

Pronounced interlayer magnetic correlations observed up to 60 Å spacer.

Interlayer coupling explained by electronic energy dependence on spin configurations.

Abstract

The magnetic properties of antiferromagnetic (AFM) EuTe epitaxial layers and short period EuTe/PbTe superlattices (SLs), grown by molecular beam epitaxy on (111) BaF$_2$ substrates, were studied by magnetization and neutron diffraction measurements. Considerable changes of the N\'eel temperature as a function of the EuTe layer thickness as well as of the strain state were found. A mean field model, taking into account the variation of the exchange constants with the strain-induced lattice distortions, and the nearest neighbor environment of a Eu atoms, was developed to explain the observed $T_{\text N}$ changes in wide range of samples. Pronounced interlayer magnetic correlations have been revealed by neutron diffraction in EuTe/PbTe SLs with PbTe spacer thickness up to 60 \AA. The observed diffraction spectra were analyzed, in a kinematical approximation, assuming partial interlayer correlations characterized by an appropriate correlation parameter. The formation of interlayer correlations between the AFM EuTe layers across the nonmagnetic PbTe spacer was explained within a framework of a tight-binding model. In this model, the interlayer coupling stems from the dependence of the total electronic energy of the EuTe/PbTe SL on the spin configurations in adjacent EuTe layers. The influence of the EuTe and PbTe layer thickness fluctuations, inherent in the epitaxial growth process, on magnetic properties and interlayer coupling is discussed.