We have studied the proximity-induced superconducting triplet pairing in CoO$_x$/Py1/Cu/Py2/Cu/Pb spin-valve structure (where Py = Ni$_{0.81}$Fe$_{0.19}$). By optimizing the parameters of this structure we found a triplet channel assisted full switch
ing between the normal and superconducting states. To observe an isolated triplet spin-valve effect we exploited the oscillatory feature of the magnitude of the ordinary spin-valve effect $Delta T_c$ in the dependence of the Py2-layer thickness $d_{Py2}$. We determined the value of $d_{Py2}$ at which $Delta T_c$ caused by the ordinary spin-valve effect (the difference in the superconducting transition temperature $T_c$ between the antiparallel and parallel mutual orientation of magnetizations of the Py1 and Py2 layers) is suppressed. For such a sample a pure triplet spin-valve effect which causes the minimum in $T_c$ at the orthogonal configuration of magnetizations has been observed.
Superconducting spin valves based on the superconductor/ferromagnet (S/F) proximity effect are considered to be a key element in the emerging field of superconducting spintronics. Here, we demonstrate the crucial role of the morphology of the superco
nducting layer in the operation of a multilayer S/F1/F2 spin valve. We study two types of superconducting spin valve heterostructures, with rough and with smooth superconducting layers, using transmission electron microscopy in combination with transport and magnetic characterization. We find that the quality of the S/F interface is not critical for the S/F proximity effect, as regards the suppression of the critical temperature of the S layer. However, it appears to be of paramount importance in the performance of the S/F1/F2 spin valve. As the morphology of the S layer changes from the form of overlapping islands to a smooth case, the magnitude of the conventional superconducting spin valve effect significantly increases. We attribute this dramatic effect to a homogenization of the Green function of the superconducting condensate over the S/F interface in the S/F1/F2 valve with a smooth surface of the S layer.
We report magnetic and superconducting properties of the modified spin valve system CoOx/Fe1/Cu/Fe2/Cu/Pb. Introduction of a Cu interlayer between Fe2 and Pb layers prevents material interdiffusion process, increases the Fe2/Pb interface transparency
, stabilizes and enhances properties of the system. This allowed us to perform a comprehensive study of such heterostructures and to present theoretical description of the superconducting spin valve effect and of the manifestation of the long-range triplet component of the superconducting condensate.
The spin valve effect for the superconducting current based on the superconductor/ferromagnet proximity effect has been studied for a CoO_x/Fe1/Cu/Fe2/Cu/Pb multilayer. The magnitude of the effect $Delta T_c$ = T_c^{AP} - T_c^{P}, where T_c^{P} and T
_c^{AP} are the superconducting transition temperatures for the parallel (P) and antiparallel (AP) orientation of magnetizations, respectively, has been measured for different thicknesses of the Fe1 layer d_{Fe1}. The obtained dependence of the effect on d_{Fe1} reveals that $Delta T_c$ can be increased in comparison with the case of a half-infinite Fe1 layer considered by the previous theory. A maximum of the spin valve effect occurs at d_{Fe1} ~ d_{Fe2}. At the optimal value of d_{Fe1}, almost full switching from the normal to the superconducting state when changing the mutual orientation of magnetizations of the iron layers Fe1 and Fe2 from P to AP is demonstrated.
