Paper detail

Enhanced Critical parameters of nano-Carbon doped MgB2 Superconductor

The high field magnetization and magneto transport measurements are carried out to determine the critical superconducting parameters of MgB2-xCx system. The synthesized samples are pure phase and the lattice parameters evaluation is carried out using the Rietveld refinement. The R-T(H) measurements are done up to a field of 140 kOe. The upper critical field values, Hc2 are obtained from this data based upon the criterion of 90% of normal resistivity i.e. Hc2=H at which Rho=90%Rho; where RhoN is the normal resistivity i.e., resistivity at about 40 K in our case. The Werthamer-Helfand-Hohenberg (WHH) prediction of Hc(0) underestimates the critical field value even below than the field up to which measurement is carried out. After this the model, the Ginzburg Landau theory (GL equation) is applied to the R-T(H) data which not only calculates the Hc2(0) value but also determines the dependence of Hc2 on temperature in the low temperature high field region. The estimated Hc(0)=157.2 kOe for pure MgB2 is profoundly enhanced to 297.5 kOe for the x=0.15 sample in MgB2-xCx series. Magnetization measurements are done up to 120 kOe at different temperatures and the other parameters like irreversibility field, Hirr and critical current density Jc(H) are also calculated. The nano carbon doping results in substantial enhancement of critical parameters like Hc2, Hirr and Jc(H) in comparison to the pure MgB2 sample.