Superconducting properties of Fe/V/Fe sandwiches

A study has been made of the superconducting properties of Fe/V/Fe sandwiches with V thickness ranging from 153 AP (atomic planes) to 5048 AP. All 20 samples studied were prepared in a single run. At zero magnetic field, the suppression of the transition temperature follows an inverse square dependence on the thickness, implying a strong pair-breaking effect in the Fe layers. The upper critical field data cross over smoothly from the 2D regime to the 3D regime with increasing V thickness. A comparison with some thin-film theories is given.     

Recovering critical stresses in sandwiches using through-the-thickness reinforcement

The paper is aimed at investigating the effects of stitching or tufting on displacement and stress fields of sandwiches, whose homogenised mechanical properties are computed through virtual material tests with 3D finite element analysis. After that, structural analysis is carried out using the adaptive model by the authors, which has variable representation of displacements across the thickness and fixed degrees of freedom. This choice is done considering its accuracy and computational efficiency. Numerical applications show that using these technical skills it is possible to considerably reduce stresses and displacements in sandwiches.     

Superconducting critical current in MoN

Journal of Materials Science Letters -     

Superconducting critical temperature in disordered tin and lead

Three-micrometer-thick tin and lead films were irradiated at temperatures below 7.2K with 25-MeV oxygen ions. The radiation-induced residual resistivity _B , superconducting critical temperature T _c , and transition width T were measured as a function of dose and subsequent thermal annealing. For tin it is found that T _c is mainly a function of _B with the detailed nature of the defects being of minor importance. Quantitative agreement with theory is obtained considering two effects: an enhancement of the isotropic part of the electron-phonon interaction and a smearing out of its anisotropic part with decreasing mean free path of the electrons. For lead the change of T _c depends on the defect configuration and it is shown that dislocation loops produce a significant T _c increase. A possible phonon contribution to T _c due to different vibrational modes of the radiation-induced defects and the host is discussed.This work received financial support from the Bundesministerium für Forschung and Technologie.     

超导临界电流测量方法与原理

超导材料的临界电流特性是材料最主要的特性之一,总结了在工程测量中临界电流的定义与判别方法;简要概括了目前5种超导临界电流的测量方法与原理;讨论了各种方法的适用范围、测量条件、测量参量、测量结果以及测量精度和测量过程能得到的材料的其它信息;把几种测量方法作了总结对比,为选择超导材料电流测量方案提供参考。     

Depairing critical currents in superfluid 3He

Critical currents in both superfluid ³He-A and ³He-B are calculated within a weak coupling model. The Fermi liquid correction is explicitly included. As a by-product we obtain the nonlinear superfluid densities in ³He-A and ³He-B, which depend strongly on the current.Work supported by National Science Foundation under Grant No. DMR76-21032.     

Computerized measuring system for critical currents in superconductors

A fully automatic measuring system for critical currents in short samples of straight superconducting wire is reported.     

Superconducting current switches for multiple superconducting critical current samples

A superconducting current switch is described, several of which can be stacked in a parallel array to allow the selection of a given sample to receive the high-current input from two current leads from the outside. The switch is a coil of superconducting wire which, when driven normal by a heater, shunts the current to a parallel, less-resistive leg. If such switches are stacked in parallel and (n ? 1) driven normal, all current goes through the superconducting member and its related sample. The configuration described here employs six switches with a test-current capability of 112 A to any sample.     

Parameters affecting critical currents in superconducting Nb3Al

A.c. susceptibility measurements made on samples of Nb₃Al have shown that, even after extensive heat-treatments, significant amounts of degraded A15 phases are present. This low critical field material, resulting from vacancies on the niobium chains, limits the current carrying capacity of the bulk sample. The indication is that under favourable conditions the critical current density of Nb₃Al could equal or be superior to that of Nb₃Sn.     

Proximity-effect theory in thickNS sandwiches

The tunneling density of states of planeNS sandwiches with a normal interlayer thicknessd is calculated. The self-consistent account of the coordinate dependence of the order parameter both inN andS metals as well as of elastic scattering from impurities was considered. The range of the sandwich parameter values is found, where the density of states can have a double-peak structure even at perfect interface. This double-peak structure was obtained earlier in the tunnel McMillan model, which assumed the presence of the tunneling barrier between theN andS layers. Thus, the Andreev reflection effects can result in a large variety of density of states of thickNS sandwiches and, in particular, to the double-peak structure.     

Investigation of critical currents of ternary molybdenum sulfides

The effect of preparation technique and pressure on the critical current densityj _c for PbMo ₆ S ₈ and SnMo ₆ S ₈ is investigated. It is shown thatj _c is significantly influenced by preparation technique. The lower limit forj _c at 4.2 K is 2 · 10 ⁴ A/cm ² in a field of 80 kOe. Measurements of the pressure dependence of the critical currents are carried out in the 0–4 kbar pressure range at 4.2 K in magnetic fields up to 90 kOe. A strong decrease ofj _c with pressure is observed.     

Inspection of intrinsic critical currents for spin-transfer magnetization switching

We examined the relationships between critical current, I/sub c/, and switching time, /spl tau//sub p/, for spin-transfer switching in two regions: (region I) /spl tau//sub p//spl Gt//spl tau//sub 0/, where thermal switching is accompanied and (region II) /spl tau//sub p/< several tens times /spl tau//sub 0/, where /spl tau//sub 0/ is the attempt time for thermal switching (/spl ap/1 ns). We estimated I/sub c0/, defined as the intrinsic I/sub c/ at 0 K, for both regions and confirmed experimentally that those I/sub c0/ coincided with each other at room temperature (RT). The value of I/sub c/ at /spl tau//sub p/=1 ns, measured with microwaves, was approximately 1.6 times the I/sub c0/. This suggested that we use at least two times I/sub c0/ as the writing currents of magnetic memory devices for nsec spin-transfer switching at RT. Although I/sub c0/ for both regions were defined as I/sub c/ at 0 K (I/sub c//sup 0K/) in theory, they showed temperature dependence at low temperatures; |I/sub c0/| for region I increased with decreasing temperature, and the estimated I/sub c//sup 0K/ was approximately three times I/sub c0/ for RT. This temperature dependence was quite different from that for region II.     

Persistent currents and critical velocities in3He-4He mixtures

Using the method of Doppler-shifted fourth sound, we have investigated the angular velocity _c1 for the onset of vorticity, the saturated critical velocity, and the dependence of _s/ onv _n –v _s for⁴He in three different pore sizes and for three different mixtures of ³ He- ⁴ Hein one of the powders used. These are the first measurements of critical velocities in ³ He- ⁴ He mixtures. We observe only a weak dependence of _c1on the pore size and within the limits of the experiment no dependence on concentrationX up toX=0.11. We find, however, that the maximumv _n –v _s attainable increases as the concentration of ³ He increases forX0.17. The observed dependence of the superfluid density onv _n –v _s is approximately two orders of magnitude stronger than predicted.     

A critical review and some results of recently developed refined theories of fiber-reinforced laminated composites and sandwiches

A critical review of literature pertinent to the subject matter of this paper was carried out under the following two broad headings: free vibration and transient dynamics. Each of these groups describes the various theoretical developments in fiber reinforced laminated composite and sandwich plates. The theoretical developments are further classified according to the refinement/accuracy of the theories developed, such as the classical theory, the first-order shear deformation theory, and the three-dimensional elasticity/higher-order shear deformation theories. The present literature review is limited to linear free vibration and transient dynamic analyses, and geometric nonlinear transient response of multilayer sandwich/fiber-reinforced composite plates. A comparative study of recently developed refined theories in conjunction with the C° isoparametric finite element formulation has been made and the conclusions were drawn based on the literature review and the refined theories results. In order to compare the present results with the available results and to provide an easy means for future comparisons by other investigators, the numerical results are presented in tabular form.     

Superconducting gap function and upper critical field in the presence of inhomogeneous magnetic order

Rare earth ternary superconductors are known to exhibit oscillatory magnetic orders below their superconducting transition temperatures. The study of behaviour of superconducting electrons in an inhomogeneous magnetic field is therefore important for such systems. We report here the results of our theoretical study of superconducting gap function Δ(T) and upper critical fieldH _c2 (T). The results are applied to analyse and explain the variation of Δ(T) andH _c2 (T) in case of NdRh₄B₄.     

Hysteresis of critical currents of superconducting bridges in low perpendicular magnetic fields

Hysteresis of critcal currentsI _c of superconducting bridges with In, Nb, and NbN has been studied in low perpendicular magnetic fields. Influences of bridge geometry, small field sweep, trapped flux, and bombardment of argon ions on the hysteresis were made clear. The experimental results suggest that the edge pinning and trapped flux in the bank of bridges are associated with the hysteresis. The peak value ofI _c of NbN bridges, as well as granular Al and In bridges reported before, in decreasing fields agrees with the calculated pair-breaking current. The origin of the hysteresis is discussed.     

Evidence for the hydrodynamic origin of critical heat currents in helium II

It is found that the critical heat current measured in a modulated heat flow in superfluid He II is substantially larger than in a steady flow. The variation of critical heat current with the modulation frequency and amplitude is shown to be analogous to the enhancement of stability observed in the flow of conventional fluids.Work supported by a grant from the National Foundation, GP13381.     

Fatigue behaviour of aluminium foam sandwiches

Aluminium foam sandwiches are subjected to four‐point bending fatigue test considering the effect of geometric parameters of panels, such as core and plate thickness, and loading mode, such as arm distance. Fatigue strength curves are expressed in terms of different stress amplitude parameters calculated using an analytical model based on laminated plate classical theory and a solid finite element method model. Despite, the notable fatigue data scatter, originated by foam intrinsic inhomogeneity, experimental fatigue curves are coherent and allow obtaining unified fatigue curves.