Enhanced critical parameters of nanocarbon doped MgB2 superconductor

Abstract

The high field magnetization and magnetotransport measurements are carried out to determine the critical superconducting parameters of MgB 2−x C x system. The synthesized samples are pure phase and the lattice parameter evaluation is carried out using the Rietveld refinement. The R − T͑H͒ measurements are done up to a field of 140 kOe. The upper critical field values, H c2 , are obtained from these data based on the criterion of 90% of normal resistivity, i.e., H c2 = H at which =90% N , where N is the normal resistivity, i.e., resistivity of about 40K in our case. The Werthamer-Helfand-Hohenberg prediction of H c2 ͑0͒ underestimates the critical field value even below the field up to which measurement is carried out. After this model, the Ginzburg-Landau theory is applied to the R − T͑H͒ data which not only calculate the H c2 ͑0͒ value but also determine the dependence of H c2 on temperature in the low temperature high field region. The estimated H c2 ͑0͒ = 157.2 kOe for pure MgB 2 is profoundly enhanced to 297.5 kOe for the x = 0.15 sample in MgB 2−x C x series. Magnetization measurements are done up to 120 kOe at different temperatures and the other parameters such as irreversibility field H irr and critical current density J c ͑H͒ are also calculated. The nano carbon doping results in substantial enhancement of critical parameters such as H c2 , H irr , and J c ͑H͒ in comparison to the pure MgB 2 sample.

Electron paramagnetic resonance and Raman spectroscopy studies on carbon-doped MgB2 superconductor nanomaterials

“…It should be noted that for C doping into MgB 2 , the carbons can either substitute into boron sites or into interstitial sites within boron rings and grain boundaries. 23,38 The very small increase in lattice parameter c shown in Fig. 1(b) may be related to interstitial C substitution into MgB 2 .…”

Effect of Ce Substitution on the Magnetoresistivity and Flux Pinning Energy of the Bi2Sr2Ca1−x Ce x Cu2O8+δ Superconductors

“…By using the ρ = ρ N (90 % ) relation, where ρ N is the normal state resistivity at the critical temperature, , related to each field value [51], the upper critical fields of samples are obtained and presented in Fig. 4.…”

Development of Doped ${\rm MgB}_{2}$ Wires and Tapes for Practical Applications

“…So far, the only element well known to increase BB c2 is carbon. The significant improvements of B c2 B in carbon doped samples have been reported by several groups [25][26][27][28]. Figure 4 shows the temperature dependence of BB c2 and B irr for the pure MgB 2 B tapes and nano-C doped samples, where the BB c2 and B irr B obtained from the 10% and 90% values of the normal-state resistance ρ.…”