Search

The electrical transport properties of (Li,Fe)OHFeSe films have been investigated in detail. The sharply textured films, prepared by matrix-assisted hydrothermal epitaxy (MHE) on LaAlO3, show a zero-resistance critical temperature T c of ∼42 K, J c values well above 1 MA cm−2 at low temperatures, and a maximum pinning force density F P of ∼100 GN m−3 at 4 K. The activation energy U 0 for thermal depinning of flux lines has been resolved for low magnetic fields, it agrees well with literature data. The coherence lengths and penetration depth were estimated via upper critical field B c2 and self-field J c, respectively, to be ξ ab ∼ 2.7 nm, ξ c = 0.24 nm, and λ ab ∼ 160–200 nm. The layered crystal structure leads to highly anisotropic and two-dimensional electrical properties, including trapping and lock-in of vortices.

The present study focuses on the effects of standby time of the MgB2 samples immersed in synthetic engine oil on the critical current density (Jc(H)), magnetic field dependence of the pinning force density fp(b) and Tc performances of MgB2 bulk superconductors. Synthetic engine oil was used as a product which is cheap and a rich carbon source. Manufactured MgB2 pellet samples were immersed at different standby time of 30 min, 120 min, 300 min and 1440 min in synthetic engine oil after the first heating process. Finally, MgB2 samples immersed in synthetic engine oil were sintered at 1000 °C and kept for 15 min in Ar atmosphere. The critical current density of all of MgB2 samples immersed at different standby time in engine oil in whole field range was better than that of the pure MgB2 sample because of the number of the pinning centers. The MgB2 sample immersed at 300 min standby time in synthetic engine oil has the best performance compared to other samples. The Jc value for the pure sample is 2.0 × 103A/cm2, whereas for the MgB2 sample immersed at 300 min standby time in engine oil the Jc is enhanced to 4.8 × 103A/cm2 at 5 K and 3 T. The superconducting transition temperature (Tc) did not change with the increasing standby time of the samples in synthetic engine oil at all. The best diamagnetic property was obtained from the sample which kept in synthetic engine oil for 300 min. Synthetic engine oil treatment results in remarkable improvement of the critical current density and pinning force performances of MgB2 superconductors. It was found that all MgB2 samples have a different pinning property at different measuring temperatures. Using synthetic engine oil as a product which is cheap and a rich carbon source in MgB2 bulk superconductors makes MgB2 samples immersed in synthetic engine oil a good candidate for industrial applications. © 2016 Elsevier B.V. All rights reserved., 13182, All the authors would like to thank Prof. Dr. Ali Gencer (at Ankara University, Ankara, Turkey) for his support and encouragement and Sahure Geçer (at Ankara University, Ankara, Turkey) for the technical assistance. This work was supported by the Scientific Research Coordination Unit of Karadeniz Technical University of Turkey, with project No: 13182.

The Jc(H) of nano-Al doped MgB2 samples has been calculated from M(H) loop measurements at different temperatures. Normalized volume pinning forces as a function of the reduced field have been analyzed at different temperatures and doping level which was taken from the Jc(H) data. The modified scaling law was used as discussed by the Eisterer to analyze the pinning forces. This law was compared with the scaling law used by the Fietz and co-worker. The grain boundary pinning is found the dominant pinning mechanism in all the doped samples and exhibit the scaling behavior. The XRD and temperature dependence of resistivity confirms the successful substitution of nano-Al at Mg sites. The results endorse that the magnetic anisotropy decreased from pure to the dirty limit with the doping of the nano-Al. The enhancement in the Jc(H) of the sample with the nano-Al doping is due to decrease in the anisotropy and increase in the volume pinning forces. The 2 % nano-Al doped sample between 15–30K shows the highest Jc(H) among all the samples.

Understanding the variation of the superconducting properties as a function of the maximum heat treatment temperature or heating time in jelly-roll Nb/sub 3/Al wire is important for the optimization of the rapid heating conditions. Jelly-roll Nb/sub 3/Al wires with a Nb matrix were ohmically-heated to maximum temperatures ranging from 1900 to 2300 /spl deg/C in vacuum in order to optimize the rapid heating conditions and to investigate the superconducting properties for this transformation method. The diameter of the wire was 0.94 mm. The sample was monitored using a noncontact measurement technique employing a photodiode to measure high temperatures (over 2000 /spl deg/C) during rapid heating. After the surface temperature reached a maximum, the sample was quenched in liquid gallium. The samples were annealed for 10 hours at 800 /spl deg/C after the rapid heating process to transform the bcc-phase to the A15 phase. The superconducting properties including DC magnetization and critical current were explored for various maximum heating temperatures and heating times.

11p; International audience; The model of thermally activated relaxation developed and successfully tested on high-Tc superconductors [Phys. Rev. B 70 (2004) 0245251-9] was applied to magnetic data of a bulk spark-plasma sintered MgB2 sample to elucidate its magnetic relaxation behavior. MgB2 and the related borides form a superconductor class lying between classical and high-Tc superconductors. In accord with this classification, the relaxation phenomena were found to be about ten times weaker than in cuprates. Vortex pinning analyzed in terms of the field dependence of the pinning force density indicates a combined pinning by normal point-like defects and by grain surfaces. An additional mode of pinning at rather high magnetic fields (of still unknown origin) was observed.