We study the superconducting properties of a series of Fe/V/Fe trilayers with variable thickness of the Fe layer and constant thickness of the V layer. For an optimized combination of thicknesses and structural quality of the thin films we observe a re-entrant behavior of the superconducting state when plotting the superconducting transition temperature T c as a function of the Fe thickness d Fe . With increasing d Fe , T c drops sharply up to d Fe Ӎ8 Å, then the superconductivity disappears, and it restores again at d Fe у12 Å.

We studied superconducting V layers deposited on an antiferromagnetically coupled [Fe(2)V(11)](20) superlattice. The parallel upper critical magnetic field exhibits an anomalous T dependence up to the ferromagnetic saturation field of the superlattice, indicating that the superconducting transition temperature T(S) decreases when rotating the relative sublattice magnetization directions of the superlattice from antiparallel to parallel. This proves that the pair breaking effect of a Fe2 layer is reduced if at a distance of 1.5 nm a second Fe2 layer with antiparallel spin orientation exists.

Epitaxial V/PdT_xFe x (001) bilayers with a V thickness of the order of 40 nm and with a Pd~_xFe x thickness in the range from 0.8 nm to 4.4 nm were prepared by molecular beam epitaxy techniques. The Curie temperature of the Pd~_xFe x layers varies between 90 and 250 K. For a bilayer with a Pdt_~Fe x thickness of 1.2 nm the ferromagnetic resonance measurements revealed a decrease of the effective magnetization 4nMee r of the ferromagnetic layer below the superconducting transition temperature of V. Asa possible explanation for this decrease we suggest a spatial modulation of the ferromagnetic order in the Pd~_xFe x layer due to modifications of the indirect exchange interaction of magnetic ions vŸ conduction electrons in the superconducting state. A comparison with a recent theoretical investigation supports this possibility.