Magnetic interactions in EuTe epitaxial layers and EuTe/PbTe superlattices

The magnetic properties of the antiferromagnetic (AFM) EuTe epitaxial layers and the short period EuTe/PbTe superlattices (SLs), grown by molecular-beam epitaxy on (111) BaF2 substrates, were studied by magnetization and neutron-diffraction measurements. Considerable changes of the Neel 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 Eu atoms, was developed to explain the observed T-N changes in a wide range of samples. Pronounced interlayer magnetic correlations have been revealed by neutron diffraction in EuTe/PbTe SL's with PbTe spacer thickness of up to 60 Angstrom. 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 the 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 the adjacent EuTe layers. The influence of the EuTe and PbTe layer thickness fluctuations, inherent in the epitaxial growth process, on the magnetic properties and interlayer coupling is discussed.