Co-current Doping Effect of Nanoscale Carbon and Aluminum Nitride on Critical Current Density and Flux Pinning Properties of Bulk $$\hbox {MgB}_{2}$$MgB2 Superconductors

Abstract

The effect of nanoscale aluminum nitride (n-AlN) and carbon (n-C) co-doping on superconducting properties of polycrystalline bulk $$\hbox {MgB}_{2}$$ superconductor has been investigated. Polycrystalline pellets of $$\hbox {MgB}_{2}$$ , $$\hbox {MgB}_{2} + 0.5$$ wt% AlN (nano), $$\hbox {MgB}_{1.99}\hbox {C}_{0.01}$$ and $$\hbox {MgB}_{1.99}\hbox {C}_{0.01} + 0.5$$ wt% AlN (nano) have been synthesized by a solid reaction process under inert atmosphere. The transition temperature ( $$T_{\mathrm{C}})$$ estimated from resistivity measurement indicates only a small decrease for C (nano) and co-doped $$\hbox {MgB}_{2}$$ samples. The magnetic field response of investigated samples has been measured at 4, 10, and 20 K in the field range ± 6 T. $$\hbox {MgB}_{2}$$ pellets co-doped with 0.5 wt% n-AlN and 1 wt% n-C display appreciable enhancement in critical current density ( $$J_\mathrm{C}$$ ) of $$\hbox {MgB}_{2}$$ in both low ( $$\ge 3$$ times), as well as, high-field region ( $$\ge $$ 15 times). $$J_\mathrm{C}$$ versus H behavior of both pristine and doped $$\hbox {MgB}_{2}$$ pellets is well explained in the light of the collective pinning model. Further, the normalized pinning force density $$f_\mathrm{p}(= F_\mathrm{p}/F_{\mathrm{pmax}})$$ displays a fair correspondence with the scaling procedure proposed by Eisterer et al. Moreover, the scaled data of the pinning force density (i.e., $$f_\mathrm{p}{-}h$$ data) of the investigated pellets at different temperature are well interpreted by a modified Dew-Hughes expression reported by Sandu and Chee.