Features of Magnetization and Vortex System of Magnesium Diboride

The Monte Carlo method was used to numerically calculate the magnetization curves of a model sample of magnesium diboride containing various concentrations of point defects. The dynamics of penetration, propagation, and trapping of Abrikosov vortices have been investigated. The calculations showed a qualitative agreement with the experimental data obtained on a multifilamentary polycrystalline commercial magnesium diboride sample. Similar simulations were performed for a cuprate high-temperature superconductor YBCO to compare the magnetic characteristics of two materials with identical pinning distributions. Differences in the irreversibility fields and total penetration fields have been shown, as well as a twofold difference in the areas of magnetization loops for these materials, which is important for practical applications. It has been shown that the observed features can be associated with the differences in vortex-vortex interactions and different pinning efficiencies resulting from the differences in the characteristic lengths. A proposal has been made that the greater rigidity of the vortex lattice in magnesium diboride than in YBCO should lead to a greater increase in magnetization and critical current when artificial defects are added.