We study the effect of nano(n)-SiC addition on the crystal structure, critical temperature (T(c)), critical current density (J(c)) and flux pinning in MgB(2) superconductors. X-ray diffraction patterns show that all the samples have MgB(2) as the main phase with a very small amount of MgO; further, with n-SiC addition the presence of Mg(2)Si is also noted and confirmed by scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS). The T(c) value for pure MgB(2) is 18.9 K under 8 T applied field, while it is 20.8 K for the 10 wt% n-SiC doped sample under the same field. This points towards the increment in the upper critical field value with n-SiC addition. The irreversibility field (H(irr)) for the 5% n-SiC added sample reached 11.3, 10 and 5.8 T, compared to 7.5, 6.5, and 4.2 T for the pure MgB(2) at 5, 10 and 20 K, respectively. The critical current density (J(c)) for the 5 wt% n-SiC added sample is increased by a factor of 35 at 10 K and 6.5 T field and by a factor 20 at 20 K and 4.2 T field. These results are understood on the basis of superconducting condensate (sigma band) disorder and ensuing intrinsic pining due to B-site C substitution clubbed with further external pinning due to available n-SiC/Mg(2)Si pins in the composite system.
We study the effect of synthesis temperature on the phase formation in nano(n)-SiC added bulk MgB 2 superconductor. In particular we study: lattice parameters, amount of carbon (C) substitution, microstructure, critical temperature (T c ), irreversibility field substitution enhances the H c2 while the low temperature synthesis is responsible for the improvement in J c due to the smaller grain size, defects and nano-inclusion induced by C incorporation into MgB 2 matrix, which is corroborated by elaborative HRTEM (highresolution transmission electron microscopy) results. We optimized the the T c (R=0) of above 15K for the studied n-SiC doped and 750 0 C synthesized MgB 2 under 140 KOe field, which is one of the highest values yet obtained for variously processed and nanoparticle added MgB 2 in literature to our knowledge.
One of the most important properties of very recently reported FeSe based superconductors is the robustness of their superconductivity under applied magnetic field. The synthesis and control of superconductivity in FeSe based compounds is rather a difficult task. Synthesis and physical property characterization for optimized superconductivity of FeSe 1/2 Te 1/2 at 13 K is reported here. The compound crystallized in a tetragonal structure with lattice parameters a = 3.8015͑2͒ and c = 6.0280͑4͒ Å. Magnetization measurements indicated bulk superconductivity with lower critical field ͑H c1 ͒ of around 180 Oe. By applying Ginzburg-Landau theory, the H c2 ͑0͒ value is estimated to be ϳ1840 kOe for the 90% of resistive transition. A heat capacity measurement revealed bulk superconductivity by a hump at T c near 13 K and an expected decrease in the same was observed under an applied magnetic field.
We report the experimental and theoretical study on magnetic nature of Bi 3 Ni system. The structure is found to be orthorhombic (Pnma) with lattice parameters a = 8.879Å b = 4.0998Å and c = 4.099Å. The title compound is synthesized via a solid state reaction route by quartz vacuum encapsulation of 5N purity stoichiometric ingredients of Ni and Bi. The superconducting transition temperature is found to be 4.1 K as confirmed from magnetization and specific heat measurements. The lower critical field (H c1 ) and irreversibility field (H irr ) are around 150 and 3000Oe respectively at 2K. Upper critical field (Hc 2 ) as determined from in field (up to 4 Tesla) ac susceptibility is found to be around 2 Tesla at 2K. The normal state specific heat is fitted using Sommerfeld-Debye equation C(T) = γT + βT 3 +δT 5 and the parameters obtained are γ= 11.08mJ/mol-K 2 , β= 3.73mJ/mol-K 4 and δ= 0.0140mJ/mol-K 6 . The calculated electronic density of states (DOS) at Fermi level N(E F ) and Debye temperature Θ D are 4.697 states/eV per formula unit and 127.7K respectively. We also estimated the value of electron phonon coupling constant (λ) to be 1.23, which when substituted in MacMillan equation gives T c = 4.5K. Density functional (DFT) based calculations for experimentally determined lattice parameters show that Ni in this compound is non-magnetic and ferromagnetic interactions seem to play no role. The Stoner condition I*N(E F ) = 0.136 per Ni atom also indicates that system cannot have any ferromagnetism. The fixed spin moment (FSM) calculations by fixing total magnetic moment on the unit cell also suggested that this system does not exhibit any signatures of ferromagnetism. Further it is concluded that ferromagnetic interactions play no role in superconductivity of Bi 3 Ni. This is in contrast to a recent report [14] related to possibility of coexistence of superconductivity and magnetism in Bi 3 Ni. Our results will surely attract more researchers to work on superconductivity of this and similar Ni containing compounds. determined from Reitveld analysis of the studied Bi 3 Ni is given in Fig. 1(b). Results and DiscussionThe DC and AC magnetic susceptibility plots of studied Bi 3 Ni are shown in Fig. 2 and 3 respectively. Namely, Fig. 2(a) depicts the DC magnetic susceptibility (χ) in both zero-fieldcooled (FC) and field-cooled (FC) situations in temperature range of 2K to 10K. The applied field is 10Oe. Superconductivity is observed at 4.1K with a sharp diamagnetic transition in magnetic susceptibility (χ) in both ZFC and FC situations. The superconducting volume fraction seems to be around 87.6% as calculated from FC (χ). This is slightly higher than as reported in ref.13.Though an estimated value is given, still we believe estimating superconducting volume 4 fraction without exactly knowing the pinning properties is not correct. What one can safely conclude from Fig. 2(a) is that the studied Bi 3 Ni is a bulk superconductor with superconducting transition temperature (T c ) at 4.1K. The AC susceptibility of Bi 3 Ni i...
We report an easy single step synthesis route of title compound Although by now nearly two years are over after the discovery of superconductivity in C. Finally the sample was allowed to cool down to room temperature. All the heating schedules were given in one single step. The resultant compound was hard enough for transport measurements and was black in color. Typically, 1 gram of raw pellet was sealed in 2.5 cm diameter and 10 cm length high quality "thick walled" quartz tube. The X-ray diffraction pattern of the compound was taken on a Rigaku diffractometer using CuK α radiation and the Rietveld analysis was carried out to know the lattice parameters and impurities etc., if present at all. Magneto-resistivity measurement R(T)H up to 14 T Field and DC magnetic susceptibility in both zero-field-cooled (zfc) and field-cooled (fc) situations along with the isothermal magnetization (MH) measurements were carried out on a physical property measurement system (PPMS) from Quantum Design (QD). The AC susceptibility at different frequencies (33 to 9999 Hz) & different amplitudes (1 to 15 Oe) of AC drive field with 4 temperatures down to 5 K, the specific heat with temperature down to 2.2 K and thermo-electric power (TEP) were also measured on the same physical property measurement system (PPMS). Figure The upper critical field is determined using different criterion of H c2 =H at which =90% N or 50% N or 10% N , where N is the normal resistivity or resistance at about 51 K. RESULTS AND DISCUSSIONThe H c2 variation with temperature is shown in Figure 2(c). To determine H c2 (0) value, we applied Ginzburg Landau (GL) theory. The GL equation is:Where, t=T/T c is the reduced temperature [18]. DC magnetic susceptibility versus temperature plot in both zero-field-cooled (zfc) and field-cooled (fc) situations is given in Figure 3. The applied magnetic field is 50 Oe.Superconductivity sets in below 49 K, as evidenced from clear diamagnetic signal at this temperature. Although the transition seems slightly broad the same is still sharper than previous reports on polycrystalline NdFeAsO/F [14,15]. Both zfc and fc are nearly saturated below 30 K.As far as the determination of superconducting volume fraction is concerned the same cannot be ascertained without ambiguity primarily due to positive paramagnetic contribution to magnetic susceptibility from Nd/Fe moments and secondly the pinning defects and impurities hamper the real outcome. Still one can say with confidence that the studied compound is a bulk superconductor with shielding fraction above 25% and superconducting volume fraction of > 8%. 7Measurement of the AC susceptibility can be conveniently used to investigate both intergrain and intragrain vortex dynamics in superconductors [31][32][33]. Figure sample is a granular superconductor like other reported oxy-pnictides.The temperature variation of the AC susceptibility measured at different AC field amplitudes 1, 2, 4, 6, 8, 10, 12, 13 & 15 Oe is shown in Figure 5. The diamagnetic onset temperature is ~ 47.7 K...
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