Interlayer Exchange Coupling in (Ga,Mn)As-based Superlattices

The interlayer coupling between (Ga,Mn)As ferromagnetic layers in all-semiconductor superlattices is studied theoretically within a tight-binding model, which takes into account the crystal, band and magnetic structure of the constituent superlattice components. It is shown that the mechanism originally introduced to describe the spin correlations in antiferromagnetic EuTe/PbTe superlattices, explains the experimental results observed in ferromagnetic semiconductor structures, i.e., both the antiferromagnetic coupling between ferromagnetic layers in IV-VI (EuS/PbS and EuS/YbSe) superlattices as well as the ferromagnetic interlayer coupling in III-V ((Ga,Mn)As/GaAs) multilayer structures. The model allows also to predict (Ga,Mn)As-based structures, in which an antiferromagnetic interlayer coupling could be expected.Comment: 4 pages, 3 figure

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 N\'eel 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 \AA. 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.Comment: 17 pages, 19 figures, accepted to PR

Magnetic anisotropy in EuS-PbS multilayers

We present the results of ferromagnetic resonance studies of the thickness dependence of magnetic anisotropy in 2 series of EuS-PbS multilayers grown on (111) BaF2 and (100) KCl substrates with the EuS thickness varying in the range d = 6-70 Å. The anisotropy constant K was found to follow the dependence K(d) = Kv + 2Ks/d, with the surface term Ks larger for layers grown on BaF2 as compared to KCl. This difference is discussed in terms of different thermal stress-induced distortions of cubic crystal lattice of EuS. We found that the thickness of EuS layer required for the perpendicular (to the layer) magnetization is d = 2-3 Å, i.e., it is below 1 monolayer

Ferromagnetic transition in EuS-PbS multilayers

The magnetic properties of multilayers of ferromagnetic EuS intercalated with diamagnetic PbS were studied as a function of the EuS layer thickness (varying from 2 to 200 ML). The critical temperature TC of the paramagnet-ferromagnet phase transition was determined from magnetization vs temperature measurements and was found to depend on the underlying substrate [KCl (100) vs BaF2 (111)] as well as on the thickness of the EuS layer. For thick layers (dEuS˜200 ML), which mimic semibulk EuS, the TC values were found shifted with respect to the bulk EuS (about 1 K up for layers grown on KCl and about 3 K down for layers grown on BaF2). This effect is attributed to stress resulting mainly from the difference of thermal expansion coefficients between the substrate and the structure. For thin layers (dEuS2 Å magnetize in the plane of the structure