Browsing by Author "Ghorbani, SR"

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    Simulation of light C4+ ion irradiation and its enhancement to the critical current density in BaFe1.9Ni0.1As2 single crystals
    (American Scientific Publishers, 2014-07-01) Shahbazi, M; Wang, XL; Ionescu, M; Ghorbani, SR; Dou, SX; Choi, KY
    In this work, we analyse the influence of C4+ irradiation with ion flounce of 3 × 1012 up to 2.3 × 1015 ion·cm−2 on significant enhancement of the critical current density, Jc , in BaFe1.9Ni0.1As2 single crystals. Jc was increased from 0.61 × 105 up to 0.94 × 105 A/cm2 at T = 10 K and H = 0.5 T. BaFe1.9Ni0.1As2 single crystals with and without the C4+-irradiation were characterized by magneto-transport and magnetic measurements up to 13 T over a wide range of temperatures below and above the superconducting critical temperature, Tc . It is found that the C4+-irradiation causes little change in Tc , but it can greatly enhance the in-field critical current density by a factor of up to 1.5. Higher dose of C4+ ions, causes further Jc enhancement at T=10 K. furthermore, flux jumping completely disappeared at T=2 K after second C4+-irradiation. Our Monte Carlo simulation results show that all the C4+ ions end up in a well defined layer, causing extended defects and vacancies at the layer, but few defects elsewhere on the irradiation paths. Furthermore, the normal state resistivity is enhanced by the light C4+ irradiation, while the upper critical field, H c2, the irreversibility field, H irr, and Tc were affected very little. © 2014 American Scientific Publisher
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    Vortex-glass phase transition and enhanced flux pinning in C4+-irradiated BaFe1.9Ni0.1As2 superconducting single crystals
    (IOP Publishing, 2013-08-13) Shabhazi, M; Wang, XL; Ghorbani, SR; Ionescu, M; Shcherbakova, OV; Wells, FS; Pan, AV; Dou, SX; Choi, KY
    We report the effects of C4+-irradiation on the superconducting properties of BaFe1.9Ni0.1As2 single crystal. The BaFe1.9Ni0.1As2 single crystal before and after C4+-irradiation was characterized by magnetic, magneto-transport and magneto-optical techniques over a wide range of magnetic fields (0–13 T) and temperatures (2–200 K). We demonstrate that the C4+-irradiation significantly enhances the in-field critical current density (by a factor of up to 1.5 at 5 K) and induces enhanced flux jumping at 2 K, with only a small degradation (by 0.5 K) of the critical temperature, Tc. The vortex phase diagram describing the evolution of the vortex-glass transition temperature with magnetic field and the upper critical field has been resolved for the C4+-irradiated sample. For temperatures below Tc, the resistivity curves and the pinning potential were found to show good scaling, using a modified model for vortex-liquid resistivity. The vortex state is three dimensional at temperatures lower than a characteristic temperature. Good agreement between the thermally activated flux flow model, which is usually employed to account for the resistivity in the vortex-liquid region, and the modified vortex-liquid model, has been observed. © 2013 IOP Publishing