The giant magnetoresistance (GMR) of a point contact between a Co/Cu multilayer and a superconductor tip varies for different bias voltage. Direct measurement of spin polarization by Andreev reflection spectroscopy reveals that the GMR change is due to a change in spin polarization. This work demonstrates that the GMR structure can be utilized as a spin source and that the spin polarization can be continuously controlled by using an external magnetic field.

Ferromagnetic Heusler Co₂FeAl_0.5Si_0.5 epitaxial thin-films have been fabricated in the L2₁ structure with saturation magnetizations over 1200 emu/cm³. Andreev reflection measurements show that the spin polarization is as high as 80% in samples sputtered on unheated MgO (100) substrates and annealed at high temperatures. However, the spin polarization is considerably smaller in samples deposited on heated substrates.

An unconventional iron superconductor, SmO_0.7F_0.3FeAs, has been utilized to determine the spin polarization and temperature dependence of a highly spin-polarized material, La_0.67Sr_0.33MnO₃, with Andreev reflection spectroscopy. The polarization value obtained is the same as that determined using a conventional superconductor Pb but the temperature dependence of the spin polarization can be measured up to 52 K, a temperature range, which is several times wider than that using a typical conventional superconductor. The result excludes spin-parallel triplet pairing in the iron superconductor.