The principle of a novel device, which is called a superconducting spin switch or a spin valve for supercurrent, is proposed and theoretically justified. It is based on a four-layer antiferromagnet/ferromagnet/superconductor/ferromagnet spin-valve-like structure. Calculations show that this structure has either zero value or lower superconducting transition temperature for the parallel alignment of magnetizations in the ferromagnetic layers as compared with an antiparallel alignment of magnetizations. Thus, the supercurrent flowing through the superconducting layer can be switched by rotating the magnetization of the top free ferromagnetic layer by a weak external magnetic field.

We study the critical temperature T cof SFF trilayers (S is a singlet superconductor, F is a ferromagnetic metal), where the long-range triplet superconducting component is generated at noncollinear...

We have studied superconducting and magnetic properties of sputtered Fe/Nb/Fe trilayers. For a fixed Nb thickness and with changing Fe thickness, $d_{\mathrm{Fe}}$, a nonmonotonic behavior of the superconducting transition temperature $T_c$ was observed with a maximum at $d_{\mathrm{Fe}}\approx 10$ Å. The analysis of the magnetization data revealed that for $d_{\mathrm{Fe}}\le 7$ Å the Fe layer is nonmagnetic. The interpretation of the observed $T_c$ behavior is attributed to the existence of this magnetically "dead" layer and the change of the interaction of the Cooper paris with this layer at the onset of ferromagnetism for $d_{\mathrm{Fe}}\ge 7$ Å.

We report on measurements of structural, superconducting, and magnetic properties of trilayer and bilayer systems combined of superconducting Pb and ferromagnetic Fe. The Pb/Fe layers can be grown on ${\mathrm{Al}}_2{\mathrm{O}}_3$ with reasonably flat interfaces, there is no alloying of the components at the interface and Fe is found to be ferromagnetic down to the monolayer range. This is a favorable situation for an $S/F$ proximity system, since it corresponds closely to the situation treated in theoretical models. We find an oscillation of the superconducting transition temperature when plotted versus the thickness of the ferromagnetic layer, which we regard as a clear indication of an unconventional, propagating superconducting pair wave function in the Pb/Fe system. We fit our results using recent theoretical model calculations and find evidence for a strongly reduced transparency of the Pb/Fe interface. We regard this as an essential feature of the proximity effect in Pb/Fe and discuss its physical origin.

We report on the first observation of a pronounced reentrant superconductivity phenomenon in a superconductor/ferromagnet layered system. The results were obtained using a superconductor/ferromagnetic-alloy bilayer of $\mathrm{Nb}/{\mathrm{Cu}}_{1-x}{\mathrm{Ni}}_x$. The superconducting transition temperature $T_c$ drops sharply with increasing thickness $d_{\mathrm{CuNi}}$ of the ferromagnetic layer, until complete suppression of superconductivity is observed at $d_{\mathrm{CuNi}}\approx 4\mathrm{nm}$. Increasing the ${\mathrm{Cu}}_{1-x}{\mathrm{Ni}}_x$ layer thickness further, superconductivity reappears at $d_{\mathrm{CuNi}}\ge 13\mathrm{nm}$. Our experiments give evidence for the pairing function oscillations associated with a realization of the quasi-one-dimensional Fulde-Ferrell-Larkin-Ovchinnikov-like state in the ferromagnetic layer.