Magnetic nanoparticles as efficient bulk pinning centers in type-II superconductors

Enhancement of vortex pinning by magnetic nanoparticles embedded into the bulk of a type-II superconductor is studied both theoretically and experimentally. Magnetic part of the pinning force associated with the interaction between a finite-size spherical magnetic inclusion and an Abrikosov vortex is calculated in the London approximation. Calculations are supported by the experimental results obtained on sonochemically modified MgB2 superconductor with embedded magnetic Fe2O3 nanoparticles and compared to MgB2 with nonmagnetic Mo2O5 pinning centers of similar concentration and particle size distribution. It is shown that ferromagnetic nanoparticles result in a considerable enhancement of vortex pinning in large-kappa type-II superconductors.