Exchange coupling of ferromagnetic films across metallic and semiconducting interlayers

Recent results obtained in our laboratories on interlayer exchange coupling of Fe films across interlayers of iron silicides, Fe1−xSix with x = 0.5– 1, are reviewed. Samples are prepared by molecular beam epitaxy and characterized by means of low-energy electron diffraction and cross-sectional transmission electron microscopy. Coupling across interlayers of iron silicide with x ≈ 0.5 is found to be oscillatory with a strength of the order of 1 mJ m−2, and across well ordered Si interlayers (nominally x = 1) the coupling is exponentially decaying. In the latter case the maximum coupling turns out to be surprisingly strong (}6$>> 6 mJ m−2), in particular considering the fact that the electrical resistivity is found to be large. Current–voltage curves for currents across the interlayers are characteristic of electron tunnelling. Soft-x-ray emission and near-edge x-ray absorption spectroscopy further support a semiconducting nature for the nominally pure Si interlayers.