140 research outputs found
Magnetic-field-induced supercurrent enhancement in hybrid superconductor/magnetic metal structures
The dc transport properties of the (S/M)I(M/S) tunnel structure - proximity
coupled superconductor (S) and magnetic (M) layers separated by an insulator
(I) - in a parallel magnetic field have been investigated. We choose for the M
metal the one in which the effective magnetic interaction, whether it arises
from direct exchange interaction or due to configuration mixing, aligns spins
of the conducting electrons antiparallel to the localized spins of magnetic
ions. For tunnel structures under consideration, we predict that there are the
conditions when the destructive action of the internal and applied magnetic
fields on Cooper pairs is weakened and the increase of the applied magnetic
field causes the field-induced enhancement of the tunnel critical current. The
experimental realization of the novel interesting effect of the interplay
between superconducting and magnetic orders is also discussed.Comment: 6 pages 2 figure
Triple-gap superconductivity of MgB2 - (La,Sr)MnO3 composite. Which of the gaps is proximity induced?
Interplay of superconductivity and magnetism in a composite prepared of the
ferromagnetic half-metallic La_0.67Sr_0.33MnO (LSMO) nanoparticles and the
conventional s-wave superconductor MgB_2 has been studied. A few principal
effects have been found in bulk samples. With an onset of the MgB_2
superconductivity, a spectacular drop of the sample resistance has been
detected and superconductivity has been observed at temperature up to 20K.
Point-contact (PC) spectroscopy has been used to measure directly the
superconducting energy coupling. For small voltage, an excess current and
doubling of the PC's normal state conductance have been found. Conductance
peaks corresponding to three energy gaps are clearly observed. Two of these
gaps we identified as enhanced \Delta_{\pi} and \Delta_{\sigma} gaps
originating from the MgB_2; the third gap \Delta_{tr} is more than three times
larger than the largest MgB_2 gap. The experimental results provide unambiguous
evidences for a new type of proximity effect which follows the phase coherency
scenario of proximity induced superconductivity. Specifically, at low
temperature, the p-wave spin-triplet condensate with pairing energy \Delta_{tr}
is essentially sustained in LSMO but is incapable to display long-range
supercurrent response because of a phase-disordering state. The proximity
coupling to MgB_2 restores the long-range phase coherency of the triplet
superconducting state, which, in turn, enhances superconducting state of the
MgB_2.Comment: 10 pages, 6 figure
Antiferromagnetic order and dielectric gap within the vortex core of antiferromagnetic superconductor
The structure of a superconducting vortex has been studied theoretically for
a dirty antiferromagnetic superconductor (AFSC), modelling an AFSC as a doped
semi-metal with s-wave superconducting pairing and antiferromagnetic
(dielectric) interaction between electrons (holes). It is also supposed that
the quasiparticles dispersion law possesses the property of nesting. The
distribution of the superconducting and magnetic order parameters near the
vortex core is calculated. It is shown that the antiferromagnetic order, been
suppressed at large distances, is restored around the superconducting flux and
the vortex core is in fact insulating and antiferromagnetic, in stark contrast
to the normal metal cores of traditional superconductors. Moreover, our model
calculations predict that as the temperature decreases the flux region of the
superconductivity and antiferromagnetism coexistence increases.Comment: 9 pages, 3 Postscript figures,NATO Advanced Research Workshop on
"Vortex dynamics in superconductors and other complex systems" Yalta, Crimea,
Ukraine, 13-17 September 200
Observation of Josephson coupling through an interlayer of antiferromagnetically ordered chromium
The supercurrent transport in metallic Josephson tunnel junctions with an
additional interlayer made up by chromium, being an itinerant antiferromagnet,
was studied. Uniform Josephson coupling was observed as a function of the
magnetic field. The supercurrent shows a weak dependence on the interlayer
thickness for thin chromium layers and decays exponentially for thicker films.
The diffusion constant and the coherence length in the antiferromagnet were
estimated. The antiferromagnetic state of the barrier was indirectly verified
using reference samples. Our results are compared to macroscopic and
microscopic models.Comment: Phys. Rev. B (2009), in prin
Orientation effects and figures of merit in advanced 2-2-type composites based on [011]-poled domain-engineered single crystals
The paper reports new results that compare the group of performance figures of merit of piezo-active 2-2-type composites based on [011]-poled domain-engineered (1 - x)Pb(Zn1/3Nb2/3)O3-xPbTiO3 single crystals, where the main crystallographic axes in the crystal layers are rotated to tailor effective electromechanical properties and related parameters. Examples of the orientation and volume-fraction dependences of the figures of merit are analysed for the first time for the system of 2-2 single crystal/polymer composites and 2-0-2 single crystal/corundum ceramic/polymer composites at x = 0.0475-0.09. The connections between the piezoelectric coefficients, energy-harvesting figures of merit and modified figures of merit (j = 1, 2 and 3) are highlighted during rotation of the main X and Y crystallographic axes around the Z axis of the crystal layers. A similar orientation behaviour of, and and their large anisotropy are studied at specific volume fractions of the single-crystal component and for a variety of microgeometric architectures of a corundum ceramic/polymer layer with 0-3 connectivity. Maxima of the longitudinal parameters, and at x = 0.0475-0.09 and constant volume fraction of the single-crystal component of the 2-2-type composites are observed in a relatively narrow orientation range. A new performance diagram is built to show regions of a large anisotropy of and in a 2-0-2 composite and, as a result of the large piezoelectric coefficients and figures of merit, the composites show significant potential in the field of piezoelectric energy-harvesting and sensor applications. This journal is </p
The temperature fields in electrically heated wires at crisis of boiling
The self-organization processes take place in several phenomena and physical objects and in particular they arise in metals in conditions of charge transfer. At liquid helium temperature in conditions of the increase of direct current flowing through bismuth, indium and tungsten there arise unstabilities of charge carries flux and this process exhibits itself in electromagnetic oscillations generation. This instability the authors refer to the mutual influence of the current flowing through the sample and magnetic field of the current. With this heat flux density through the sample’s surfaces didn’t exceed 0.1 W/sm2. Such a value of heat flux is сlose to the first boiling crisis but the author state that the nature of these phenomena is no case is connected with the heat removal specific features
Relationship between hysteretic behavior of magnetization and magnetoresistance in half-metallic ferromagnets
A generalized Preisach description of hysteretic magnetotransport properties of half-metallic ferromagnets (HMFs) is proposed. Assuming that the system consists of an assembly of elementary bistable hysterons distributed in energy levels and with a range of possible energy barriers, the connection between irreversible magnetic and transport properties of HMFs is found. Within this model, both the magnetization hysteresis and resistivity hysteresis of HMFs can be described by a few simple assumptions common to description of hysteresis phenomena leading to some fundamental relationship
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