Determination of Spin Polarization Using an Unconventional Iron Superconductor

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.