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

Abstract

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 ${d}_{\mathrm{Fe}2}$ 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 ${d}_{\mathrm{Fe}2}<1$ nm, the superconducting transition temperature ${T}_{c}^{\mathrm{P}}$ for the parallel orientation of magnetizations of the Fe1 and Fe2 layers is smaller than that for the antiparallel orientation ${T}_{c}^{\mathrm{AP}}$, which corresponds to the direct spin-valve effect. For ${d}_{\mathrm{Fe}2}\ensuremath{\geqslant}1$ nm, we have found the inverse spin-valve effect with $\ensuremath{\Delta}{T}_{c}={T}_{c}^{\mathrm{AP}}\ensuremath{-}{T}_{c}^{\mathrm{P}}<0$. 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 ${d}_{\mathrm{Fe}2}$. The analysis of the ${T}_{c}({d}_{\mathrm{Fe}2})$ 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 $\ensuremath{\Delta}{T}_{c}({d}_{\mathrm{Fe}2})$ 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) [JETP Lett. 91, 308 (2010)]].