Spin screening of magnetic moments in superconductors

We consider ferromagnetic particles embedded into a superconductor and study the screening of their magnetic moments by the spins of the Cooper pairs in the superconductor. It is shown that a magnetic moment opposite to the one of the ferromagnetic particle is induced in the superconductor. In the case of a small itinerant ferromagnet grain and low temperatures, the full screening of the magnetic moment takes place, i.e. the absolute value of the total magnetic moment induced in the superconductor is equal to the one of the ferromagnetic particle. In type-II superconductors the proposed screening by spins of the conduction electrons can be much stronger than the conventional screening by Meissner currents.