Effect of nano-particle doping on the upper critical field and flux pinning in MgB2

The effect of nano particle doping on the critical current density of MgB₂ is reviewed. Most nano-particle doping leads to improvement of J_c(H) performance while some shows a negative effect as with Cu and Ag. Nano-carbon containing dopants have two distinguishable contributions to the enhancement of J_c field performance: increase of upper critical field and improvement of flux pinning. Among all the dopants studied so far, nano SiC doping showed the most significant and reproducible enhancement in J_c(H). The nano SiC doping introduced many precipitates at a scale below 10 nm, which serve as strong pinning centers. J_c for the nano SiC doped samples increased by more than an order of magnitude at high fields and all temperatures compared to the undoped samples. The significant enhancement in J_c(H) of nano-SiC doping has been widely verified and confirmed, having a great potential for applications. An attempt is made to clarify the controversy on the effects of nano Fe and Ti doping on J_c.