189 research outputs found
Magnetic nanoparticles as efficient bulk pinning centers in type-II superconductors
Enhancement of flux pinning by magnetic nanoparticles embedded into the bulk
of type-2 superconductor is studied both theoretically and experimentally.
Magnetic part of the pinning force associated with the interaction between a
spherical magnetic inclusion and an Abrikosov vortex was calculated in the
London approximation. Calculations are supported by the experimental results
obtained on sonochemically modified MgB2 superconductor with embedded magnetic
Fe2O3 nanoparticles and compared to MgB2 with nonmagnetic Mo2O5 pinning centers
of similar concentration and particle size distribution. It is shown that
ferromagnetic nanoparticles result in a considerable enhancement of vortex
pinning in large-kappa type-2 superconductors.Comment: PDF, 14 page
Phase diagram of a superconductor / ferromagnet bilayer
The magnetic field (H) - temperature (T) phase diagram of a superconductor is
significantly altered when domains are present in an underlying ferromagnet
with perpendicular magnetic anisotropy. When the domains have a band-like
shape, the critical temperature Tc of the superconductor in zero field is
strongly reduced, and the slope of the upper critical field as a function of T
is increased by a factor of 2.4 due to the inhomogeneous stray fields of the
domains. Field compensation effects can cause an asymmetric phase boundary with
respect to H when the ferromagnet contains bubble domains. For a very
inhomogeneous domain structure, Tc~H^2 for low H and Tc~H for higher fields,
indicating a dimensional crossover from a one-dimensional network-like to a
two-dimensional behavior in the nucleation of superconductivity.Comment: 6 pages, 7 figure
Development of an oximeter for neurology
Cerebral desaturation can occur during surgery manipulation, whereas otherparameters vary insignificantly. Prolonged intervals of cerebral anoxia can cause seriousdamage to the nervous system. Commonly used method for measurement of cerebral bloodflow uses invasive catheters. Other techniques include single photon emission computedtomography (SPECT), positron emission tomography (PET), magnetic resonance imaging(MRI). Tomographic methods frequently use isotope administration, that may result inanaphylactic reactions to contrast media and associated nerve diseases. Moreover, the high costand the need for continuous monitoring make it difficult to apply these techniques in clinicalpractice. Cerebral oximetry is a method for measuring oxygen saturation using infraredspectrometry. Moreover reflection pulse oximetry can detect sudden changes in sympathetictone. For this purpose the reflectance pulse oximeter for use in neurology is developed.Reflectance oximeter has a definite advantage as it can be used to measure oxygen saturation inany part of the body. Preliminary results indicate that the device has a good resolution and highreliability. Modern applied schematics have improved device characteristics compared withexisting ones
Surface Enhancement of Superconductivity in Tin
The possibility of surface enhancement of superconductivity is examined
experimentally. It is shown that single crystal tin samples with cold-worked
surfaces represent a superconductor with a surface-enhanced order parameter (or
negative surface extrapolation length b), whose magnitude can be controlled.Comment: 8 pages, 4 figure
Shapiro steps in a superconducting film with an antidot lattice
Shapiro voltage steps at voltages V_n=nV_0 (n integer) have been observed in
the voltage-current characteristics of a superconducting film with a square
lattice of perforating microholes (antidots)in the presence of radiofrequent
radiation. These equidistant steps appear at the second matching field H_2 when
the flow of the interstitial vortex lattice in the periodic potential created
by the antidots and the vortices trapped by them, is in phase with the applied
rf frequency. Therefore, the observation of Shapiro steps clearly reveals the
presence of mobile intersitial vortices in superconducting films with regular
pinning arrays. The interstitial vortices, moved by the driving current,
coexist with immobile vortices strongly pinned at the antidots.Comment: 6 pages text, 3 EPS figures, RevTeX, accepted for publication in PRB
Rapid Communication
Magnetic Pinning of Vortices in a Superconducting Film: The (anti)vortex-magnetic dipole interaction energy in the London approximation
The interaction between a superconducting vortex or antivortex in a
superconducting film and a magnetic dipole with in- or out-of-plane
magnetization is investigated within the London approximation. The dependence
of the interaction energy on the dipole-vortex distance and the film thickness
is studied and analytical results are obtained in limiting cases. We show how
the short range interaction with the magnetic dipole makes the co-existence of
vortices and antivortices possible. Different configurations with vortices and
antivortices are investigated.Comment: 12 pages, 12 figures. Submitted to Phys. Rev.
Magnetization reversal in long chains of submicrometric Co dots
This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics.Long chains of 400 nm diam Co dots prepared by combined electron-beam lithography exhibit interesting magnetotransport properties. The magnetoresistance of the chains of dots is markedly different from single Co films, indicating a strongly modified magnetization reversal process. Magnetic force microscopy(MFM) shows that, after magnetic saturation, in the remanent state the single-domain dots are all oriented with their magnetic moment along the chain. A comparison of the magnetoresistance and the MFM reveals that the magnetization reversal occurs by coherent rotation of the magnetic moment in the single-domain dots forming the chain
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