Observation of two species of vortices in the anisotropic spin-triplet superconductor Sr2RuO4Sr_2 Ru O_4

Magnetic flux structures in single crystals of the layered spin triplet superconductor Sr$\_{2}$RuO$\_{4}$ are studied by scanning micro SQUID Force microscopy. Vortex chains appear as the applied field is tilted along the in-plane direction of the superconductor. The vortex chains align along the direction of the in-plane component of the applied magnetic field. The decoration of in-plane vortices by crossing Abrikosov vortices is observed: two vortex orientations are apparent simultaneously, one along the layers and the other perpendicular to the layers. The crossing vortices appear preferentially on the in-plane vortices

Observation of vortex coalescence in the anisotropic spin-triplet superconductor Sr2_{2}RuO4_{4}

We present direct imaging of magnetic flux structures in the anisotropic, spin-triplet superconductor Sr$_{2}$RuO$_{4}$ using a scanning $\mu$SQUID microscope. Individual quantized vortices were seen at low magnetic fields. Coalescing vortices forming flux domains were revealed at intermediate fields. Based on our observations we suggest that a mechanism intrinsic to the material stabilizes the flux domains against the repulsive vortex-vortex interaction. Topological defects like domain walls can provide this, implying proof for unconventional chiral superconductivity.Comment: submitted to PR

Evaluation of Spin-Triplet Superconductivity in Sr2RuO4

This review presents a summary and evaluations of the superconducting properties of the layered ruthenate Sr2RuO4 as they are known in the autumn of 2011. This paper appends the main progress that has been made since the preceding review by Mackenzie and Maeno was published in 2003. Here, special focus is placed on the critical evaluation of the spin-triplet, odd-parity pairing scenario applied to Sr2RuO4. After an introduction to superconductors with possible odd-parity pairing, accumulated evidence for the pairing symmetry of Sr2RuO4 is examined. Then, significant recent progress on the theoretical approaches to the superconducting pairing by Coulomb repulsion is reviewed. A section is devoted to some experimental properties of Sr2RuO4 that seem to defy simple explanations in terms of currently available spin-triplet scenario. The next section deals with some new developments using eutectic boundaries and micro-crystals, which reveals novel superconducting phenomena related to chiral edge states, odd-frequency pairing states, and half-fluxoid states. Some of these properties are intimately connected with the properties as a topological superconductor. The article concludes with a summary of knowledge emerged from the study of Sr2RuO4 that are now more widely applied to understand the physics of other unconventional superconductors, as well as with a brief discussion of relatively unexplored but promising areas of ongoing and future studies of Sr2RuO4.Comment: 31 pages, 35 figures, published in J. Phys. Soc. Jpn. as a review article of Special Topic

Systematic motion of magnetic domain walls in notched nanowires under ultrashort current pulses

International audienceThe precise manipulation of transversemagnetic domain walls in finite/infinite nanowires with artificial defects under the influence of very short spin-polarized current pulses is investigated. We show that for a classical 3d ferromagnet material like nickel, the exact positioning of the domain walls at room temperature is possible only for pulses with very short rise and fall time that move the domain wall reliably to nearest neighboring pinning position. The influence of the shape of the current pulse and of the transient effects on the phase diagram current-pulse length are discussed. We show that large transient effects appear even when alpha = beta, below a critical value, due to the domain wall distortion caused by the current pulse shape and the presence of the notches. The transient effects can oppose or amplify the spin-transfer torque (STT), depending on the ratio beta/alpha. This enlarges the physical comprehension of the domain wall (DW) motion under STT and opens the route to the DW displacement in both directions with unipolar currents

Ferromagnetic MnCoGe thin films produced via magnetron sputtering and non-diffusive reaction

MnCoGe thin films were produced using simultaneous magnetron sputtering of Mn, Co, and Ge on SiO2, followed by non-diffusive reaction. The MnCoGe compound begins to form at ∼588 K, and structural characterizations show that the obtained MnCoGe film is polycrystalline with the hexagonal Ni2In-type structure. This structure is found to be stable from 873 K down to room temperature, the expected hexagonal/orthorhombic structural transition being prevented. The film exhibits a lower average Mn composition than the standard MnCoGe stoichiometry. Furthermore, small clusters (<3 nm) forming planar distributions parallel to the sample surface are observed. They are regularly located every∼11 nm in the specimen depth. They mainly contain Mn and O atoms. Magnetic characterizations show very good magnetic properties, allowing the perpendicular and parallel magnetocrystalline anisotropy constants to be measured down to 100 K, using the Chappert model to fit ferromagnetic resonance measurements. The film magnetic properties match the properties of bulk stoichiometric MnCoGe in the hexagonal structure, with a Curie temperature of ∼269 K and a negligible coercive field at room temperature. The only difference between the magnetic properties of bulk and thin film specimens appears to be the film shape anisotropy, forcing the internal magnetic field to be contained in the film plane.INITIATIVE D'EXCELLENCE AIX MARSEILLE UNIVERSIT