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H. Kepa

Publications and source records attributed to H. Kepa.

5 recordsLinked to original sources
arXiv2008

Interlayer coupling in EuS/SrS, EuS/PbSe and EuS/PbTe magnetic semiconductor superlatices

Neutron reflectivity studies of EuS/SrS, EuS/PbSe, and EuS/PbTe all-semiconductor superlattices were carried out in search for exchange interlayer coupling. A relatively weak antiferromagnetic coupling was found in EuS/SrS and in EuS/PbSe systems but no interlayer coupling was detected in EuS/PbTe superlattices. In EuS/SrS, where the SrS spacer is an insulator ($E_g\approx 4$ eV), a very weak and short range interlayer coupling is in agreement with the earlier theoretical predictions that the interlayer coupling strength in EuS-based magnetic semiconductor superlattices depends strongly on the energy gap of the nonmagnetic layer and should decrease with an increase of the energy gap of the spacer material. A weak coupling in EuS/PbSe and no coupling in EuS/PbTe, where both PbSe and PbTe are narrow-gap semiconductors ($E_g\approx 0.3$ eV), is in disagreement not only with the theoretical expectations but also in a stark contrast with earlier results for another narrow-gap spacer system -- EuS/PbS, where pronounced antiferromagnetic coupling persists even in samples with PbS layer thickness as large as 200 Å. A possible influence of the increasing lattice mismatch between EuS and the spacer materials (0.5%, 0.8%, 2.5%, and 8.2% for PbS, SrS, PbSe, and PbTe, respectively) on the magnetic in-plane ordering of EuS layer and, consequently, on the interlayer coupling was investigated by polarized neutron reflectometry in the case of EuS/PbTe.

cond-mat.mtrl-sci↗
arXiv2003

Probing hole-induced ferromagnetic exchange in magnetic semiconductors by inelastic neutron scattering

The effect of hole doping on the exchange coupling of the nearest neighbor (NN) Mn pairs in Zn$_{1-x}$Mn$_x$Te is probed by inelastic neutron scattering. The difference in the NN exchange energy $ΔJ_1$ in the presence and in the absence of the holes is determined. The obtained value of $ΔJ_1$ is in good agreement with the predictions of the Zener/RKKY model, even on the insulator side of the metal-insulator transition.

cond-mat.mtrl-sci↗
arXiv2003

Magnetic interactions in EuTe epitaxial layers and EuTe/PbTe superlattices

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 Néel 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 Å. 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.

cond-mat.mtrl-sci↗
arXiv2002

Interlayer Exchange Coupling in Semiconductor Magnetic/Nonmagnetic Superlattices

The interlayer spin correlations in the magnetic/non-magnetic semiconductor superlattices are reviewed. The experimental evidences of interlayer exchange coupling in different all-semiconductor structures, based on neutronographic and magnetic studies, are presented. A tight-binding model is used to explain interaction transfer across the non-magnetic block without the assistance of carriers in ferromagnetic EuS/PbS and antiferromagnetic EuTe/PbTe systems.

cond-mat.mtrl-sci↗