2,743 research outputs found
Effect of carbon nanotube doping on critical current density of MgB2 superconductor
The effect of doping MgB2 with carbon nanotubes on transition temperature,
lattice parameters, critical current density and flux pinning was studied for
MgB2-xCx with x = 0, 0.05, 0.1, 0.2 and 0.3. The carbon substitution for B was
found to enhance Jc in magnetic fields but depress Tc. The depression of Tc,
which is caused by the carbon substitution for B, increases with increasing
doping level, sintering temperature and duration. By controlling the extent of
the substitution and addition of carbon nanotubes we can achieve the optimal
improvement on critical current density and flux pinning in magnetic fields
while maintaining the minimum reduction in Tc. Under these conditions, Jc was
enhanced by two orders of magnitude at 8T and 5K and 7T and 10K. Jc was more
than 10,000A/cm2 at 20K and 4T and 5K and 8.5T, respectively
Flux pinning mechanism in BaFe1.9Ni0.1As2 single crystals: Evidence for fluctuation in mean free path induced pinning
The flux pinning mechanism of BaFe1.9Ni0.1As2 superconducting crystals have been investigated systematically by magnetic measurements up to 13 T at various temperatures. The field dependence of the critical current density, Jc, was analysed within the collective pinning model. A remarkably good agreement between the experimental results and theoretical dl pinning curve is obtained, which indicates that pinning in BaFe1.9Ni0.1As2 crystal originates from spatial variation of the mean free path. Moreover, the normalized pinning force density, Fp, curves versus h1/4B/Birr (Birr is the irreversibility field) were scaled using the Dew-Hughes model. Analysis suggests that point pinning alone cannot explain the observed field variation of Fp
Enhancement of Transition Temperature in FexSe0.5Te0.5 Film via Iron Vacancies
The effects of iron deficiency in FexSe0.5Te0.5 thin films (0.8<x<1) on
superconductivity and electronic properties have been studied. A significant
enhancement of the superconducting transition temperature (TC) up to 21K was
observed in the most Fe deficient film (x=0.8). Based on the observed and
simulated structural variation results, there is a high possibility that Fe
vacancies can be formed in the FexSe0.5Te0.5 films. The enhancement of TC shows
a strong relationship with the lattice strain effect induced by Fe vacancies.
Importantly, the presence of Fe vacancies alters the charge carrier population
by introducing electron charge carriers, with the Fe deficient film showing
more metallic behavior than the defect-free film. Our study provides a means to
enhance the superconductivity and tune the charge carriers via Fe vacancy, with
no reliance on chemical doping.Comment: 15 pages, 4 figure
Graphene micro-substrate induced high electron-phonon coupling in MgB2
Electron-phonon coupling strength was studied in graphene-MgB2 composites to explore the possibilities for a higher superconducting transition temperature (Tc). For the first time in the experimental work on MgB2, the Raman active E2g mode was split into two parts: a softened mode corresponding to tensile strain and a hardened mode attributed to the carbon substitution effect. The tensile strain effect is suggested to improve Tc of graphene-MgB2 composites because it increases the electron-phonon coupling strength of MgB2
Effect of nano-particle doping on the upper critical field and flux pinning in MgB2
The effect of nano particle doping on the critical current density of MgB2 is reviewed. Most nano-particle doping leads to improvement of Jc(H) performance while some shows a negative effect as with Cu and Ag. Nano-carbon containing dopants have two distinguishable contributions to the enhancement of Jc field performance: increase of upper critical field and improvement of flux pinning. Among all the dopants studied so far, nano SiC doping showed the most significant and reproducible enhancement in Jc(H). The nano SiC doping introduced many precipitates at a scale below 10 nm, which serve as strong pinning centers. Jc for the nano SiC doped samples increased by more than an order of magnitude at high fields and all temperatures compared to the undoped samples. The significant enhancement in Jc(H) of nano-SiC doping has been widely verified and confirmed, having a great potential for applications. An attempt is made to clarify the controversy on the effects of nano Fe and Ti doping on Jc
Magnetic properties of a novel Pr Fe Ti phase
In a systematic study of the (Pr1âxTix)Fe5 alloy series, the (Pr0.65Ti0.35)Fe5 alloy has been
found to have a dominant phase with either the rhombohedral Th2Zn17 structure or the
newly discovered Nd2(Fe,Ti)19 (S. J. Collocott, R. K. Day, J. B. Dunlop, and R. L. Davis,
in Proceedings of the Seventh International Symposium on Magnetic Anisotropy and
Coercivity in RâT Alloys, Canberra, July 1992, p. 437) structure, depending on the
annealing procedure. Powderâxârayâdiffraction patterns and scanning electron
microscopy show that the sample annealed at a temperature of 850â°C followed by
1000â°C has the 2:17 structure whereas annealing at 1000â°C directly leads to the new
2:19 structure. Energyâdispersive xâray analysis yields Pr:Fe:Ti ratios of 10.7:86.2:3.1
for the Pr2(Fe,Ti)17 phase and 9.2:85.9:4.9 for the Pr2(Fe,Ti)19 phase.
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Fe Mössbauer
spectroscopy (at 295 K) gives values for the average
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Fe hyperfine field of 15.7 T for the
2:17 phase and 17.5 T for the 2:19 phase, respectively
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