Magnetic phase diagram and critical current of BaFe2As2 single crystals with hole- and electron-doping
We report on comparative study of magnetic phase diagram and critical current of the hole- and electron-doped BaFe2As2 single crystals with close values of superconducting critical temperature, Tc, (slightly underdoped Ba0.64K0.36Fe2As2 with Tc=25K and optimally doped BaFe1.9Ni0.1As2 with Tc=20K) obtained from measurements of the temperature dependence
of ac-susceptibility and isothermal irreversible magnetization loops, M(H), in magnetic fields parallel to the c-axis of the crystal. From ac-susceptibility measurements we get estimation of a slope of the upper critical eld, Hc2, in dependence on temperature, dHc2/dT =- 4.2T/K for BaFe1:9Ni0:1As2 single crystal and dHc2/dT =-1.75T/K for Ba0.64K0.36Fe2As2 sample that in accordance with Werthamer, Helfand, and Hohenberg (WHH) model gives Hc2(0) = 0.69Tc((dHc2)/dT) = 56T for BaFe1.9Ni0.1As2 sample and lower value of Hc2(0) = 31T for Ba0.64K0.36Fe2As2 crystal. However, obtained from M(H) measurements temperature dependence of the irreversibility field, Hirr(T), for BaFe1.9Ni0.1As2 crystal located below the
one for Ba0.64K0.36Fe2As2 crystal. Furthermore, at T=4.2K and higher temperatures our results for critical current density, Jc, calculated from M(H) curves clearly show slower reduction of Jc with increasing field for even underdoped Ba0.64K0.36Fe2As2 sample compared to optimally doped BaFe1.9Ni0.1As2 crystal demonstrating higher capacity of K-doped 122 compounds for production of superconducting cables and wires with high critical current in strong magnetic
We report on successful fabrication of superconducting FeSe wire using hot gas extrusion (HGE) ex-situ PIT (powder in tube) method. Length of the obtained wire was about 60cm with cross-sectional superconducting core area nearly 2.5x 10^-3 cm^2. For the wire sample we observed superconducting transition temperature, T_onset = 11 K, about 1.2K lower compared to the preliminary prepared FeSe powder. Heat treatment in argon atmosphere at 350C resulted in transition width decrease from \Delta T(10% - 90%) = 1.75K in sample without heat treatment down to \Delta T = 0.9 K in annealed samples. Estimated derivative of the upper critical eld as a function of temperature of the sample annealed during 72h in argon atmosphere at 350C is dHc2/dT =2.9 T/K. Applying WHH theory to our data allows to define Hc2(0K) = 0.69Tc x(dHc2/dT )= 19.8T. The untreated wire shows critical current density, Jc = 75 A/cm2 at T=4.0 K in zero field. Increasing annealing time up to 72 hours at 350C in argon atmosphere gives rise to Jc increase of about 60% approaching 120 A/cm2 at T=4.0K and H=0T . Also Jc measurements were made in magnetic fields up to 9T. Our results show applicability of the HGE PIT method for fabrication of superconducting wires based on FeSe compound. Long-range heat treatment is necessary to improve superconducting properties of the samples.
We investigate numerically the formation of vortex–antivortex pairs in thin-film superconducting strip in the presence of a straight current-carrying wire, oriented perpendicular to this strip. We demonstrate that the change in the number of the trapped vortices/antivortices inside the strip near the current-carrying wire results in a oscillatory dependence of the critical current Ic on the magnitude of the control current Iw in the wire. We consider the effect of the width of the superconducting strip and the width of the control wire on the period and the amplitude of the dc-Josephson-like oscillations of the critical current.
The dynamics of a two-component Davydov-Scott (DS) soliton with a small mismatch of the initial location or velocity of the high-frequency (HF) component was investigated within the framework of the Zakharov-type system of two coupled equations for the HF and low-frequency (LF) fields. In this system, the HF field is described by the linear Schrödinger equation with the potential generated by the LF component varying in time and space. The LF component in this system is described by the Korteweg-de Vries equation with a term of quadratic influence of the HF field on the LF field. The frequency of the DS soliton`s component oscillation was found analytically using the balance equation. The perturbed DS soliton was shown to be stable. The analytical results were confirmed by numerical simulations.
Radiation conditions are described for various space regions, radiation-induced effects in spacecraft materials and equipment components are considered and information on theoretical, computational, and experimental methods for studying radiation effects are presented. The peculiarities of radiation effects on nanostructures and some problems related to modeling and radiation testing of such structures are considered.
This volume presents new results in the study and optimization of information transmission models in telecommunication networks using different approaches, mainly based on theiries of queueing systems and queueing networks .
The paper provides a number of proposed draft operational guidelines for technology measurement and includes a number of tentative technology definitions to be used for statistical purposes, principles for identification and classification of potentially growing technology areas, suggestions on the survey strategies and indicators. These are the key components of an internationally harmonized framework for collecting and interpreting technology data that would need to be further developed through a broader consultation process. A summary of definitions of technology already available in OECD manuals and the stocktaking results are provided in the Annex section.