RESUMO
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.
RESUMO
The effect of hole doping on the exchange coupling of the nearest neighbor (NN) Mn pairs in Zn(1-x)MnxTe is probed by inelastic neutron scattering. The difference in the NN exchange energy DeltaJ1 in the presence and in the absence of the holes is determined. The obtained value of DeltaJ1 is in good agreement with the predictions of the Zener/RKKY model, even on the insulator side of the metal-insulator transition.
