Physical properties of the superconducting spin-valve Fe/Cu/Fe/In heterostructure

We report on structural, magnetic, and superconducting properties of the spin-valve multilayer system CoO_x/Fe1/Cu/Fe2/In. For most of the thicknesses of the second iron layer d_Fe2 up to 2 nm, we have observed a full spin-valve effect for the superconducting current, i.e., a complete transition from the normal to the superconducting state by changing the mutual orientation of the magnetizations of the Fe1 and Fe2 layers. For d_Fe2<1 nm, the superconducting transition temperature T_c^P for the parallel orientation of magnetizations of the Fe1 and Fe2 layers is smaller than that for the antiparallel orientation T_c^AP, which corresponds to the direct spin-valve effect. For d_Fe2⩾1 nm, we have found the inverse spin-valve effect with ΔT_c=T_c^AP−T_c^P<0. Further, in samples with a fixed thickness of the In layer, we have observed an oscillating dependence of its superconducting transition temperature T_c on d_Fe2. The analysis of the T_c(d_Fe2) dependence using the theory of the superconducting-ferromagnetic proximity effect has enabled determination of all microscopic parameters of the studied system. With these parameters, a satisfactory description of the sign-changing oscillating behavior of the spin-valve effect ΔT_c(d_Fe2) has been obtained using a recent theory by Fominov et al. [ Ya. V. Fominov et al. Pis'ma Zh. Eksp. Teor. Fiz. 91 329 (2010).