  Heterogeneous sonochemical method was applied for synthesis of novel
superconducting nanocomposites consisting of magnetic (and/or nonmagnetic)
nanoparticles embedded into the bulk of ceramic superconductors. In addition to
in-situ production of the efficient pinning centers, this synthesis method
considerably improves the interbrain coupling. Significant enhancement of the
magnetic irreversibility is reported for Fe2O3 nanoparticles embedded into the
bulk of MgB2 superconductor. Nonmagnetic Mo2O5 nanoparticles also increase
pinning strength, but less than magnetic Fe2O3. Detailed magnetization and
electron microscopy characterization is presented. Theory of bulk magnetic
pinning due to ferromagnetic nanoparticles of finite size embedded into the
superconducting matrix is developed.
