Magnetic Studies of MgB2Prepared by Internal Magnesium Diffusion With Various Doping

Abstract

MgB2 wires doped with carbon and SiO2 nanoparticles prepared by the modified internal magnesium diffusion method were studied and compared with an undoped reference sample. It was found that doping of boron powder has a substantial effect on the diffusion reaction and that carbon acts as a MgB2 growth suppressor. The highest critical current density was exhibited by the wire with SMI+C boron powder heat-treated at 650 °C/1 h, with almost 10 000 $\text{A}\cdot\text{cm}^{-2}$ at 10 T and 4.2 K. From the point of view of pinning behavior, this wire showed the lowest pinning energies, indicating that high $J_{c}$ is due to an increased number of pinning sites. The other C-doped wire with the PVZ+C boron powder showed field-direction-dependent pinning energies with higher energies for the parallel direction, in good agreement with the $J_{c}$ results. The SiO2-doped wires exhibited a wide flux jump region and a quickly declining field dependence of $J_{c}$ .