Direct observation of the flux-line vortex glass phase in a type II superconductor

The order of the vortex state in La_{1.9} Sr_{0.1} CuO_{4} is probed using muon spin rotation and small-angle neutron scattering. A transition from a Bragg glass to a vortex glass is observed, where the latter is composed of disordered vortex lines. In the vicinity of the transition the microscopic behavior reflects a delicate interplay of thermally-induced and pinning-induced disorder.Comment: 14 pages, 4 colour figures include

Asymmetry of spin wave dispersions in a hexagonal magnonic crystal

We report a study of the dispersion of spin waves in a hexagonal array of interacting ferromagnetic nanodisks for two orthogonal orientations of the in-plane applied magnetic field, i.e., either parallel or perpendicular to the direction of first neighbour disks. The experimental data were modelled using the dynamical matrix method, and the results were interpreted in terms of the effective wave vector model. We have found that spin waves propagating in the two orthogonal directions exhibit marked asymmetry concerning the existence of maxima/minima in their dispersion curves and the sign of their group velocities

Asymmetry of spin wave dispersions in a hexagonal magnonic crystal

PublishedJournal ArticleWe report a study of the dispersion of spin waves in a hexagonal array of interacting ferromagnetic nanodisks for two orthogonal orientations of the in-plane applied magnetic field, i.e., either parallel or perpendicular to the direction of first neighbour disks. The experimental data were modelled using the dynamical matrix method, and the results were interpreted in terms of the effective wave vector model. We have found that spin waves propagating in the two orthogonal directions exhibit marked asymmetry concerning the existence of maxima/minima in their dispersion curves and the sign of their group velocities. © 2013 AIP Publishing LLC.This work was supported by the European Community's Seventh Framework Programme (FP7/2007-2013) under Grant Agreement Nos. 228673 (MAGNONICS) and 233552 (DYNAMAG) and by MIUR-PRIN 2010-11 Project 2010ECA8P3 “DyNanoMag.” V.V.K. also acknowledges funding received from EPSRC of the UK under project EP/E055087/1

Muons as Local Probes of Three-body Correlations in the Mixed State of Type-II Superconductors

The vortex glass state formed by magnetic flux lines in a type-II superconductor is shown to possess non-trivial three-body correlations. While such correlations are usually difficult to measure in glassy systems, the magnetic fields associated with the flux vortices allow us to probe these via muon-spin rotation measurements of the local field distribution. We show via numerical simulations and analytic calculations that these observations provide detailed microscopic insight into the local order of the vortex glass and more generally validate a theoretical framework for correlations in glassy systems.Comment: 4+ pages, high-quality figures available on reques

Emergent propagation modes of ferromagnetic swimmers in constrained geometries

PublishedJournal ArticleThis is the author accepted manuscript. The final version is available from AIP Publishing via the DOI in this record.Magnetic microswimmers, composed of hard and soft ferromagnets connected by an elastic spring, are modelled under low Reynolds number conditions in the presence of geometrical boundaries. Approaching a surface, the magneto-elastic swimmer's velocity increases and its trajectory bends parallel to the surface contour. Further confinement to form a planar channel generates new propagation modes as the channel width narrows, altering the magneto-elastic swimmer's speed, orientation, and direction of travel. Our results demonstrate that constricted geometric environments, such as occuring in microfluidic channels or blood vessels, may influence the functionality of magneto-elastic microswimmers for applications such as drug delivery.We acknowledge the financial support from EC Contract No. 665440 “ABIOMATER.

Ferromagnetic/superconducting proximity effect in La0.7Ca0.3MnO3 / YBa2Cu3O7 superlattices

We study the interplay between magnetism and superconductivity in high quality YBa2Cu3O7 (YBCO) / La0.7Ca0.3MnO3(LCMO)superlattices. We find evidence for the YBCO superconductivity depression in presence of the LCMO layers. We show that due to its short coherence length superconductivity survives in the YBCO down to much smaller thickness in presence of the magnetic layer than in low Tc superconductors. We also find that for a fixed thickness of the superconducting layer, superconductivity is depressed over a thickness interval of the magnetic layer in the 100 nm range. This is a much longer length scale than that predicted by the theory of ferromagnetic/superconducting proximity effect.Comment: 10 pages + 5 figures, submitted to Phys. Rev.

Anomalous Superconducting Properties and Field Induced Magnetism in CeCoIn5

In the heavy fermion superconductor CeCoIn5 (Tc=2.3K) the critical field is large, anisotropic and displays hysteresis. The magnitude of the critical-field anisotropy in the a-c plane can be as large as 70 kOe and depends on orientation. Critical field measurements in the (110) plane suggest 2D superconductivity, whereas conventional effective mass anisotropy is observed in the (100) plane. Two distinct field-induced magnetic phases are observed: Ha appears deep in the superconducting phase, while Hb intersects Hc2 at T=1.4 K and extends well above Tc. These observations suggest the possible realization of a direct transition from ferromagnetism to Fulde-Ferrel-Larkin-Ovchinnikov superconductivity in CeCoIn5.Comment: 4 pages, 3 figure

Influence of surface anisotropy on exchange resonance modes in spherical shells

This is the author accepted manuscript. The final version is available from IOP Publishing via the DOI in this recordThe dynamical properties of saturated spherical shells are investigated in the exchange-dominated regime when assuming that surface anisotropy is present at both the inner and outer boundaries. It is found that surface anisotropy plays an important role in determining the dependence of lower-order eigenvalues on shell thickness. The mode frequency can increase with decreasing shell thickness, or is driven rapidly towards the ferromagnetic resonance frequency depending on the choice of the surface anisotropy constant at each boundary. The presence of surface anisotropy significantly modifies the size dependence of the modes which can be suppressed or amplified based on the coupling between boundaries. When surface anisotropy is present only on the outer boundary, similar behaviour to the solid sphere is observed for lower-order eigenvalues up to a thickness of after which large deviations begin to occur, where and are the inner and outer radius, respectively. Moreover, surface anisotropy introduces a dependence of the zeroth mode on shell thickness, removing the degeneracy with the ferromagnetic resonance and leading to a pronounced size dependence of this mode for thin shells.The authors acknowledge financial support from the Defense Science and Technology Laboratory (DSTL) and the Engineering and Physical Sciences Research Council (EPSRC) of the United Kingdom, via the EPSRC Centre for Doctoral Training in Electromagnetic Metamaterials (Grant No. EP/L015331/1)