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

Neutron reflectivity studies of EuS/SrS, EuS/PbSe and EuS/PbTe all-semiconductor superlattices were carried out in a search for exchange interlayer coupling. A relatively weak antiferromagnetic coupling was found in EuS/SrS and 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)≈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)≈0.3 eV), is in disagreement not only with the theoretical expectations but also in stark contrast with earlier results for another narrow-gap spacer system, EuS/PbS, where pronounced antiferromagnetic coupling persists even in samples with PbS layer thicknesses 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 ordering of the EuS layer near the interfaces and, consequently, on the interlayer coupling is discussed.

Novel superconducting semiconducting superlattices: dislocation-induced superconductivity?

Novel superconducting superlattices with transition temperature in the range 2.5-6.4 K consisting only of semiconducting materials are discovered. Among them there are multilayers, including a wide-gap semiconductor as one of the components. It is shown that superconductivity is connected with the interfaces between two semiconductors containing regular grids of the misfit dislocations. The possibility of the dislocation-induced superconductivity is discussed.