Superconducting spintronics has emerged in the past decade as a promising new field that seeks to open a new dimension for nanoelectronics by utilizing the internal spin structure of the superconducting Cooper pair as a new degree of freedom 1,2 . Its basic building blocks are spin-triplet Cooper pairs with equally aligned spins, which are promoted by proximity of a conventional superconductor to a ferromagnetic material with inhomogeneous macroscopic magnetization 3 . Using low-energy muon spin-rotation experiments we find an unanticipated e ect, in contradiction with the existing theoretical models of superconductivity and ferromagnetism: the appearance of a magnetization in a thin layer of a non-magnetic metal (gold), separated from a ferromagnetic double layer by a 50-nm-thick superconducting layer of Nb. The e ect can be controlled either by temperature or by using a magnetic field to control the state of the remote ferromagnetic elements, and may act as a basic building block for a new generation of quantum interference devices based on the spin of a Cooper pair.The ability to manipulate the spin degree of freedom of charge carriers is key to realizing future spin-based electronics. Integrating superconductors into spintronic devices can greatly enhance performance 1 and allows the transport of spin over long distances without the dissipation of heat 2 . To achieve the alignment of electron spins, ferromagnetic materials are used. Superconductivity and ferromagnetism are, however, antagonistic states of matter, and the interplay between these two states results in the conversion of conventional spin-singlet into spin-triplet pair correlations 3 . Whereas spin-singlet pairs have spin angular momentum S = 0, spin-triplet pairs have S = 1, with three possible spin projections s z = −1, 0, +1. The realization of such spin-triplet pairs in mesoscopic systems containing interfaces between superconducting (S) and ferromagnetic (F) layers has attracted much interest from both the theoretical and experimental communities. Interaction of spin-singlet superconductivity with collinear ferromagnetism leads to oscillations and suppression of the pair correlation at a short distance ξ f due to the exchange magnetic field in the ferromagnet, which tends to align the spins of electrons parallel 4-7 . However, to create longer-range penetration of spin-triplet superconductivity into the ferromagnet, interaction with a non-collinear magnetism is required [8][9][10] , motivating the discovery of superconducting currents through ferromagnetic metals over distances far longer than the singlet penetration length ξ f (refs 11-13). These long-range triplet components (LRTC) have parallel spin projections (s z = ±1), and are not suppressed by the exchange field. Theory predicts that the conversion into spin-triplet pairs should also give rise to an induced magnetic moment in the superconductor, decaying away from the interface [14][15][16] , often called the inverse or magnetic proximity effect. For diffusive systems this induced m...

The induced magnetic moment, provided by the bands electrons, is calculated in a variety of Josephson junctions with multilayered ferromagnetic (F) weak link. The noncollinear magnetization of the F layers provides the conditions necessary to generate triplet superconducting correlations. It leads to the long-range induced magnetic moment, emerging in the superconducting (S) layers. It is shown to be dependent on the Josephson phase. By tuning the Josephson current, one may control the long-range induced magnetic moment. Alternatively, applying the voltage we can generate an oscillatory magnetic moment. The detection of such a spin effect may serve as independent evidence of the triplet superconductivity. The proposed mechanism seems to be attractive for superconducting spintronic devices with low dissipation.Comment: 5 pages, 2 figures, submitted to Applied Physics Letter

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Transport measurements are presented on thin-film superconducting spin-valve systems, where the controlled noncollinear arrangement of two ferromagnetic Co layers can be used to influence the superconducting state of Nb. We observe a very clear oscillation of the superconducting transition temperature with the relative orientation of the two ferromagnetic layers. Our measurements allow us to distinguish between the competing influences of domain averaging, stray dipolar fields, and the formation of superconducting spin triplets. Domain averaging is shown to lead to a weak enhancement of transition temperature for the antiparallel configuration of exchange fields, while much larger changes are observed for other configurations, which can be attributed to drainage currents due to spin triplet formation. The normally antagonistic ground states of conventional superconductivity and ferromagnetism give rise to a variety of intriguing phenomena when brought into close proximity, a subject that has gained much attention both theoretically [1][2][3][4][5][6][7][8][9] and experimentally [10][11][12][13][14][15][16][17][18] over recent years. The underlying proximity effect of singlet Cooper pairs penetrating a ferromagnetic (F ) layer is nonmonotonic in nature, which is very different from the monotonic decay found for the case of proximity coupling into a normal (N ) metal. This unconventional proximity effect leads, for example, to oscillations in the critical temperature (T c ) of the superconductor as function of the thickness of the F layer [19][20][21].In 2002 the superconducting spin valve was proposed theoretically [22,23], comprising a superconducting (S) spacer layer separating two F layers. For ideal operation, the supercurrent in the S layer can be controlled by switching the relative orientation of the exchange fields (H ex ) of the F layers from a parallel (P) to an antiparallel (AP) alignment. The underlying physical mechanism involves the interaction of the singlet Cooper pair with both exchange fields, whereby it experiences an additional pair dephasing if the device is in the P state, due to a potential energy mismatch between the spin up and spin down electron of the penetrated pair, thus lowering T c . Such an effect does not occur in the AP case, since both electrons find themselves in equivalent bands. This mechanism can be generalized as a relative enhancement of T c by domain averaging and has been observed in a variety of experiments [24][25][26][27][28], where, with the exception of Ref.[25], a pinned magnetic layer is used to create the AP arrangement. However, several seemingly anomalous results with precisely the opposite behavior have also been reported [29][30][31][32][33]. One plausible explanation proposed for these results, in systems * Corresponding author: mgf@st-andrews.ac.uk where no pinning layer was used, is the dominance of a suppression of superconductivity by dipolar fields generated by the domains [25]. In experimental work caution therefore needs to be exercised to avoid a dom...