P. J. Curran
University of Bath
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Publication
Featured researches published by P. J. Curran.
Physical Review B | 2015
M. G. Flokstra; T.C. Cunningham; J. Kim; Nathan Satchell; Gavin Burnell; P. J. Curran; S. J. Bending; C. J. Kinane; J. F. K. Cooper; S. Langridge; A. Isidori; N.G. Pugach; Matthias Eschrig; S. L. Lee
(Received 10 April 2014; revised manuscript received 13 January 2015; published 2 February 2015) 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.
Nature Physics | 2016
M. G. Flokstra; Nathan Satchell; J. Kim; Gavin Burnell; P. J. Curran; S. J. Bending; J. F. K. Cooper; C. J. Kinane; S. Langridge; A. Isidori; N.G. Pugach; Matthias Eschrig; H. Luetkens; A. Suter; T. Prokscha; Stephen Leslie Lee
A switchable induced magnetic moment in a non-magnetic metal that is separated from a ferromagnet by a thick superconducting layer contradicts existing models.
Physical Review B | 2014
S. J. Ray; Alexandra S. Gibbs; S. J. Bending; P. J. Curran; Egor Babaev; C. Baines; A. P. Mackenzie; S. L. Lee
Muon-spin rotation has been used to probe the vortex state in Sr2RuO4. At moderate fields and temperatures a lattice of triangular symmetry is observed, crossing over to a lattice of square symmetr ...
Journal of Applied Physics | 2010
T. J. Hayward; Adam D. West; K. J. Weatherill; P. J. Curran; P. W. Fry; P. M. Fundi; M.R.J. Gibbs; T. Schrefl; C. S. Adams; Ifan G. Hughes; S. J. Bending; Dan A. Allwood
We present a design for a switchable nanomagnetic atom mirror formed by an array of 180° domain walls confined within Ni80Fe20 planar nanowires. A simple analytical model is developed which allows the magnetic field produced by the domain wall array to be calculated. This model is then used to optimize the geometry of the nanowires so as to maximize the reflectivity of the atom mirror. We then describe the fabrication of a nanowire array and characterize its magnetic behavior using magneto-optic Kerr effect magnetometry, scanning Hall probe microscopy, and micromagnetic simulations, demonstrating how the mobility of the domain walls allow the atom mirror to be switched “on” and “off” in a manner which would be impossible for conventional designs. Finally, we model the reflection of R87b atoms from the atom mirror’s surface, showing that our design is well suited for investigating interactions between domain walls and cold atoms.
Applied Physics Letters | 2015
P. J. Curran; J. Kim; Nathan Satchell; James Witt; Gavin Burnell; M. G. Flokstra; S. L. Lee; J. F. K. Cooper; C. J. Kinane; S. Langridge; A. Isidori; N.G. Pugach; Matthias Eschrig; S. J. Bending
We demonstrate that the magnetic state of a superconducting spin valve, that is normally controlled with an external magnetic field, can also be manipulated by varying the temperature which increases the functionality and flexibility of such structures as switching elements. In this case, switching is driven by changes in the magnetostatic energy due to spontaneous Meissner screening currents forming in the superconductor below the critical temperature. Our scanning Hall probe measurements also reveal vortex-mediated pinning of the ferromagnetic domain structure due to the pinning of quantized stray fields in the adjacent superconductor. The ability to use temperature as well as magnetic field to control the local magnetisation structure raises the prospect of potential applications in magnetic memory devices.
Physical Review B | 2017
V. Kozhevnikov; Anne-Marie Valente-Feliciano; P. J. Curran; A. Suter; Albert Yung-hsu Liu; Goezt M Richter; E. Morenzoni; S. J. Bending
The standard interpretation of the phase diagram of type-II superconductors was developed in the 1960s and has since been considered a well-established part of classical superconductivity. However, upon closer examination a number of fundamental issues arises that leads one to question this standard picture. To address these issues we studied equilibrium properties of niobium samples near and above the upper critical field Hc2 in parallel and perpendicular magnetic fields. The samples investigated were very high quality films and single-crystal disks with the Ginzburg-Landau parameters 0.8 and 1.3, respectively. A range of complementary measurements has been performed, which include dc magnetometry, electrical transport, muon spin rotation spectroscopy, and scanning Hall-probe microscopy. Contrary to the standard scenario, we observed that a superconducting phase is present in the sample bulk above Hc2 and the field Hc3 is the same in both parallel and perpendicular fields. Our findings suggest that above Hc2 the superconducting phase forms filaments parallel to the field regardless of the field orientation. Near Hc2 the filaments preserve the hexagonal structure of the preceding vortex lattice of the mixed state, and the filament density continuously falls to zero at Hc3. Our paper has important implications for the correct interpretation of the properties of type-II superconductors and can be essential for practical applications of these materials.
Scientific Reports | 2015
P. J. Curran; Waled M Desoky; M. V. Milošević; Chaves A; Laloë Jb; Jagadeesh S. Moodera; S. J. Bending
Scanning Hall probe microscopy (SHPM) has been used to study vortex structures in thin epitaxial films of the superconductor MgB2. Unusual vortex patterns observed in MgB2 single crystals have previously been attributed to a competition between short-range repulsive and long-range attractive vortex-vortex interactions in this two band superconductor; the type 1.5 superconductivity scenario. Our films have much higher levels of disorder than bulk single crystals and therefore both superconducting condensates are expected to be pushed deep into the type 2 regime with purely repulsive vortex interactions. We observe broken symmetry vortex patterns at low fields in all samples after field-cooling from above Tc. These are consistent with those seen in systems with competing repulsions on disparate length scales, and remarkably similar structures are reproduced in dirty two band Ginzburg-Landau calculations, where the simulation parameters have been defined by experimental observations. This suggests that in our dirty MgB2 films, the symmetry of the vortex structures is broken by the presence of vortex repulsions with two different lengthscales, originating from the two distinct superconducting condensates. This represents an entirely new mechanism for spontaneous symmetry breaking in systems of superconducting vortices, with important implications for pinning phenomena and high current density applications.
Journal of Superconductivity and Novel Magnetism | 2018
V. Kozhevnikov; Anne-Marie Valente-Feliciano; P. J. Curran; G. Richter; A. Volodin; A. Suter; S. J. Bending
Equilibrium magnetic properties of the mixed state in type II superconductors were studied on high-purity film and single-crystal niobium samples with different Ginzburg-Landau parameters in perpendicular and parallel magnetic fields using dc magnetometry and scanning Hall-probe microscopy. The magnetization curve for samples with unity demagnetizing factor (slabs in perpendicular field) was obtained for the first time. It was found that none of the existing theories is consistent with these new data. To address this problem, a theoretical model is developed and comprehensively validated. The new model describes the mixed state in an averaged limit, i.e., without detailing the samples’ magnetic structure and therefore ignoring the surface current and interactions between the structural units (vortices). At low values of the Ginzburg-Landau parameter, it converts to the model of Peierls and London for the intermediate state in type I superconductors. The model quantitatively describes the magnetization curve for the perpendicular field and provides new insights into the properties of the mixed state, including properties of individual vortices. In particular, it suggests that description of the vortex matter in superconductors of the transverse geometry as a “gas-like” system of non-interacting vortices is more appropriate than the frequently used solid-like scenarios.
Scientific Reports | 2017
Estefani Marchiori; P. J. Curran; J. Kim; Nathan Satchell; Gavin Burnell; S. J. Bending
High resolution scanning Hall probe microscopy has been used to directly visualise the superconducting vortex behavior in hybrid structures consisting of a square array of micrometer-sized Py ferromagnetic disks covered by a superconducting Nb thin film. At remanence the disks exist in almost fully flux-closed magnetic vortex states, but the observed cloverleaf-like stray fields indicate the presence of weak in-plane anisotropy. Micromagnetic simulations suggest that the most likely origin is an unintentional shape anisotropy. We have studied the pinning of added free superconducting vortices as a function of the magnetisation state of the disks, and identified a range of different phenomena arising from competing energy contributions. We have also observed clear differences in the pinning landscape when the superconductor and the ferromagnet are electron ically coupled or insulated by a thin dielectric layer, with an indication of non-trivial vortex-vortex interactions. We demonstrate a complete reconfiguration of the vortex pinning potential when the magnetisation of the disks evolves from the vortex-like state to an onion-like one under an in-plane magnetic field. Our results are in good qualitative agreement with theoretical predictions and could form the basis of novel superconducting devices based on reconfigurable vortex pinning sites.
Journal of Physics: Condensed Matter | 2017
Nathan Satchell; James Witt; Gavin Burnell; P. J. Curran; C. J. Kinane; Timothy R. Charlton; S. Langridge; J. F. K. Cooper
We characterise the magnetic state of highly-textured, sputter deposited erbium for a film of thickness 6 nm. Using polarised neutron reflectometry it is found that the film has a high degree of magnetic disorder, and we present some evidence that the films local magnetic state is consistent with bulk-like spiral magnetism. This, combined with complementary characterisation techniques, show that thin film erbium is a strong candidate material for incorporation into device structures.