Traditional studies that combine spintronics and superconductivity have mainly focused on the injection of spin-polarized quasiparticles into superconducting materials. However, a complete synergy between superconducting and magnetic orders turns out to be possible through the creation of spin-triplet Cooper pairs, which are generated at carefully engineered superconductor interfaces with ferromagnetic materials. Currently, there is intense activity focused on identifying materials combinations that merge superconductivity and spintronics to enhance device functionality and performance. The results look promising: it has been shown, for example, that superconducting order can greatly enhance central effects in spintronics such as spin injection and magnetoresistance. Here, we review the experimental and theoretical advances in this field and provide an outlook for upcoming challenges in superconducting spintronics.At the interface between materials with radically different properties, new physical phenomena can emerge. A classical example of such an interface is that between a superconductor and a ferromagnet where the opposing electron orders destructively interfere; however, it turns out that under the right conditions at a superconductorferromagnet interface both superconductivity and spin-polarization can unite to create a new superconducting state that offers tantalizing possibilities for spin transport in which Joule heating and dissipation are minimized.Spintronics offers the potential for creating circuits in which logic operations controlled by spin currents can be performed faster and more energy efficient [1] than the charge-based equivalent in semiconductor transistor technologies. Spintronics is one of the most active areas of research and while it offers control of spin and charge at the nanometer scale, it has also found sensory applications in hard disk drive read heads via the giant magnetoresistance effect [2,3]. The idea of combining superconductivity with spintronics has historically focused on the net spin-polarization of quasiparticles in superconductors. It is interesting to note that the first spin transport experiments [4-6] involved ferromagnet-superconductor bilayers and predated non-superconducting spin transport experiments [8]. As will be discussed in this review, it is possible to create pseudo-chargeless spin-1/2 excitations in superconductors [7] which have extremely long spin lifetimes.Recently, a more complete synergy between superconductivity and spintronics has been made possible through the discovery of spin-triplet Cooper pairs at superconductor-ferromagnet interfaces. Non-superconducting spin currents are generated by passing charge currents through ferromagnetic materials. As will be explained in this review, spin currents can also be generated by passing supercurrents through ferromagnetic materials. Charge flow within superconductors is carried by Cooper pairs which consist of interacting pairs of electrons [9]. The idea of combining superconducting and magnetic order wa...

The superconductor-ferromagnet proximity effect describes the fast decay of a spin-singlet supercurrent originating from the superconductor upon entering the neighboring ferromagnet. After placing a conical magnet (holmium) at the interface between the two, we detected a long-ranged supercurrent in the ferromagnetic layer. The long-range effect required particular thicknesses of the spiral magnetically ordered holmium, consistent with spin-triplet proximity theory. This enabled control of the electron pairing symmetry by tuning the degree of magnetic inhomogeneity through the thicknesses of the holmium injectors.

We report magnetic and electrical measurements of Nb Josephson junctions with strongly ferromagnetic barriers of Co, Ni and Ni80Fe20 (Py). All these materials show multiple oscillations of critical current with barrier thickness implying repeated 0-π phase-transitions in the superconducting order parameter. We show in particular that the Co barrier devices can be accurately modelled using existing clean limit theories and so that, despite the high exchange energy (309 meV), the large IcRN value in the π-state means Co barriers are ideally suited to the practical development of superconducting π-shift devices.

Unlike conventional spin-singlet Cooper pairs, spin-triplet pairs can carry spin. Triplet supercurrents were discovered in Josephson junctions with metallic ferromagnet spacers, where spin transport can occur only within the ferromagnet and in conjunction with a charge current. Ferromagnetic resonance injects a pure spin current from a precessing ferromagnet into adjacent non-magnetic materials. For spin-singlet pairing, the ferromagnetic resonance spin pumping efficiency decreases below the critical temperature (T) of a coupled superconductor. Here we present ferromagnetic resonance experiments in which spin sink layers with strong spin-orbit coupling are added to the superconductor. Our results show that the induced spin currents, rather than being suppressed, are substantially larger in the superconducting state compared with the normal state; although further work is required to establish the details of the spin transport process, we show that this cannot be mediated by quasiparticles and is most likely a triplet pure spin supercurrent.

We report a systematic study of Nb/ferromagnet ͑FM͒/Nb trilayer structures in which the FM layer is one of the strong ferromagnets Co, Fe, Ni, and Ni 80 Fe 20 ͑Py͒. Accurate control of the FM layer thickness has enabled detailed studies of the magnetic and transport properties in the superconducting state. In all cases, we estimate the thickness of the magnetic dead layer and the exchange energies of the ferromagnetic layers; in doing so, we demonstrate inconsistencies between the exchange energies derived elsewhere from superconductor ͑S͒/FM bilayer experiments and from S/FM/S junction measurements compared to their bulk Curie temperatures, which may hint at further complexity in the underlying physics. We show results in support of a recent publication ͓J. W. A Robinson et al., Phys. Rev. Lett. 97, 177003 ͑2006͔͒, focus in detail on a single 0-phase transition, and show evidence for the appearance of a second harmonic in the current-phase relation at the minimum of the critical current.Thin films of Nb/ Co/ Nb, Nb/Py/Nb, Nb/ Ni/ Nb, and Nb/ Fe/ Nb were prepared on thermally oxidized ͑100͒ Si substrates with a 250 nm oxide layer on the surface in an PHYSICAL REVIEW B 76, 094522 ͑2007͒