Spin-polarized tunneling and spin injection in superconductor-ferromagnet junctions

We present non-equilibrium phenomena in ferromagnet/superconductor/ferromagnet tunnel junctions. In the junctions, spin polarization induced by the spin-polarized tunneling competes with the superconductivity. As a result, a variety of non-linear superconducting and magnetoresistive phenomena are expected. The superconducting critical current observed experimentally in ferromagnetic manganite/high-Tc superconductor tunnel junctions is analyzed. We also discuss the spin current backflow accompanied by the Josephson current caused by the spin injection.