  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 \AA.
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.
