PROBING FERROMAGNETS WITH ANDREEV REFLECTION

High transmissivity, ferromagnet-superconductor thin film nanocontacts are studied experimentally. Compared to nonmagnetic metal-superconduc tor contacts, Andreev reflection is strongly suppressed due to the spi n polarization of conduction electrons in the ferromagnet. This effect is used to measure both the transparency of the interface and spin po larization of the direct current in the ferromagnet in contrast to the spin polarization of the tunneling current previously measured in fer romagnet-insulator-superconductor systems. [S0031-9007(98)07318-9].