308 research outputs found
Theory of the tunneling spectroscopy of ferromagnetic superconductors
We study tunneling conductance in normal metal / insulator / ferromagnetic
superconductor junctions. The tunneling spectra show a clear difference between
spin-singlet s-wave pairing, spin-triplet opposite spin pairing and
spin-triplet equal spin pairing: These pairings exhibit, respectively, gap
struture, double peak structure and zero bias peak in the spectra. The obtained
result may serve as a tool for determining the pairing symmetry of
ferromagnetic superconductors.Comment: 4 pages, 2 figure
Magnetic and transport parameters of LSMO and YBCO/LSMO films deposited on sapphire substrates
The La0.7Sr0.3MnO3 (LSMO) layers and YBa2Cu3O7-{\delta}/La0.7Sr0.3MnO3
(YBCO/LSMO) bilayers were grown by magnetron sputtering on sapphire (Al2O3 or
ALO) substrates. Temperature dependences of resistance of single LSMO films,
grown on ALO substrates were typical for polycrystalline manganite materials
and the resistance decreased with decrease of the temperature at medium
temperatures and increased at lower and higher temperatures. Deposition of a
top YBCO layer led to a drastic increase of the sample resistance. These
bilayers did not demonstrate a decreasing of the resistance with decrease of
temperature. Temperature dependence of the resistance of these samples was
interpreted in the framework of a phenomenological model of two intergrain
conduction channels. In framework of this model, parameters of the samples were
determined and discussed
Pairing symmetry signatures of T1 in superconducting ferromagnets
We study the nuclear relaxation rate 1/T1 as a function of temperature for a
superconducting-ferromagnetic coexistent system using a p-wave triplet model
for the superconducting pairing symmetry. This calculation is contrasted with a
singlet s-wave one done previously, and we see for the s-wave case that there
is a Hebel-Slichter peak, albeit reduced due to the magnetization, and no peak
for the p-wave case. We then compare these results to a nuclear relaxation rate
experiment on UGe2 to determine the possible pairing symmetry signatures in
that material. It is seen that the experimental data is inconclusive to rule
out the possibility of s-wave pairing in .Comment: 4 pages, 4 figure
Physical properties of ferromagnetic-superconducting coexistent system
We studied the nuclear relaxation rate 1/T1 of a
ferromagnetic-superconducting system from the mean field model proposed in
Ref.14. This model predicts the existence of a set of gapless excitations in
the energy spectrum which will affect the properties studied here, such as the
density of states and, hence, 1/T1. The study of the temperature variation of
1/T1(for T<Tc) shows that the usual Hebel-Slichter peak exists, but will be
reduced because of the dominant role of the gapless fermions and the background
magnetic behavior. We have also presented the temperature dependence of
ultrasonic attenuation and the frequency dependence of electromagnetic
absorption within this model. We are successful in explaining certain
experimental results.Comment: 10 Pages, 9 figute
Surface Effects in Superparamagnetic Magnetite Particles *
Abstract. We have studied the properties of unshielded and shielded (hybrid) nanosized spherical magnetite particles with diameter 10 ± 2 nm, which are superparamagnetic at room temperature, through magnetometry, X-ray powder diffraction, magnetic force microscopy imaging and Mössbauer spectroscopy. The unshielded material was prepared by co-precipitation either in air or in inert atmosphere and part of it was shielded subsequently by β-cyclodextrin (β-C42H70O35). The studies indicated that in the unshielded particles there is a surface layer with a depth of 3 nm wherein an exponential rise in the number of vacancies is observed in the octahedral sublattice ([B]-sites), so that the particle surface is highly defective and could be represented by the general formula (Fe , where x = 0-0.3 and denotes vacancies. In contrast, the hybrid particles, being protected from oxidation, are structurally close to bulk magnetite so that the surface magnetic effects could be understood as due to the chaotic orientation of the magnetic moments at the magnetic-nonmagnetic material interface. An empirical model for a spherical single domain particle was developed in attempting to describe the evolution of structural defects in the surface layer
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