Magnetic Studies of MgB2 Prepared by Internal Magnesium Diffusion With Various Doping

MgB
₂
wires doped with carbon and SiO
₂
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 MgB
₂
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 A · 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 SiO
₂
-doped wires exhibited a wide flux jump region and a quickly declining field dependence of J
_c
.