Ferromagnet–superconductor hybrids

Abstract

A new class of phenomena discussed in this review is based on interaction between spatially separated, but closely located ferromagnets and superconductors. They are called Ferromagnet-Superconductor Hybrids (FSH). These systems include coupled smooth and textured Ferromagnetic and Superconducting films, magnetic dots, wires etc. The interaction may be provided by the magnetic flux from magnetic textures and supercurrents. The magnetic flux from magnetic textures or topological defects can pin vortices or create them, changing drastically the properties of the superconductor. On the other hand, the magnetic field from supercurrents (vortices) strongly interacts with the magnetic subsystem leading to formation of coupled magnetic-superconducting topological defects. We discuss possible experimental realization of the FSH. The presence of ferromagnetic layer can change dramatically the properties of the superconducting film due to proximity effect. We discuss experimental and theoretical studies of the proximity effect in the FSH including transition temperature, order parameter oscillations and triplet superconductivity.

Magnetic confinement of the superconducting condensate in superconductor-ferromagnet hybrid composites

“…In such S-F hybrids the proximity effect 4 as well as the stray fields of the ferromagnet 5 play an important role in changing the superconducting properties. A magnetic template which creates a nonuniform magnetic field distribution is able to localize the superconducting condensate ͑or normal electrons 6 ͒.…”

Growth of [110] La2∕3Sr1∕3MnO3–YBa2Cu3O7 heterostructures

“…The magnetic response of the structure at T Ͻ T sc shows both diamagnetic and ferromagnetic moments with ͓001͔ direction as magnetic easy axis. While the superconducting transition temperature ͑T sc ͒ of these structures is sharp ͑⌬T sc Ӎ 2.5 K͒, the critical current density ͑J c ͒ follows a dependence of the type J c = J o ͑1−T / T sc ͒ 3/2 with highly suppressed J o ͑Ӎ2 ϫ 10 4 A/cm 2 The transport of quasiparticles and paired electrons across superconductor ͑SC͒-ferromagnet ͑FM͒ proximity effect junctions provides valuable information on the degree of spin polarization in the ferromagnet, exchange-field-induced inhomogeneous superconductivity at the SC-FM interface, symmetry of the SC order parameter, and a plethora of other effects arising from the antagonism between superconductivity and ferromagnetism, 1-3 some of which are technologically important. 4,5 There have been extensive studies of polarized and unpolarized quasiparticle injection in conventional s-wave superconductors.…”

“…After the deposition of the PBCO layer the substrate temperature was raised to 750°C keeping the p O 2 constant. The growth of 300 Å thick LSMO was carried out at 2 , and G r Ӎ 0.5 Å / s. Once the growth of the LSMO layer was complete, a 1000 Å YBCO film was deposited on top of the PBCO-LSMO bilayer at T d = 800°C, p O 2 = 0.4 mbar, E d ϳ 2 J/cm 2 , and G r Ӎ 1.6 Å / s. After completion of this layer, the deposition chamber was filled with O 2 to atmospheric pressure and then the sample was cooled to room temperature with a 30 min holdup at 500°C to realize full oxygenation of the structure. These deposition parameters were established after taking a series of calibration runs where the crystal orientation, high T sc of the YBCO, and low coercivity ͑H c ͒ of the LSMO layer were important factors in deciding the best condition.…”

London study of vortex states in a superconducting film due to a magnetic dot

“…The aforementioned systems are not only important for technological applications, such as devices that can be tuned by weak magnetic fields, but also offer rich physical effects which are not observed in the individual parts. Some of these effects were predicted elsewhere [2][3][4][5][6][7].In the recent decade, magnetic dots growing on top of SC films have been extensively studied both experimentally [8] and theoretically [9,10]. In experimental studies, magnetic dots with in-plane magnetization are fabricated from Co, Ni, Fe, Gd-Co and Sm-Co alloys, whereas, for the dots with magnetization perpendicular to the plane, Co/Pt multilayers are used [11].…”

“…In the recent decade, magnetic dots growing on top of SC films have been extensively studied both experimentally [8] and theoretically [9,10]. In experimental studies, magnetic dots with in-plane magnetization are fabricated from Co, Ni, Fe, Gd-Co and Sm-Co alloys, whereas, for the dots with magnetization perpendicular to the plane, Co/Pt multilayers are used [11].…”