Determination of the surface spin-polarization of perovskite oxides using point-contact Andreev reflection spectroscopy

Materials with surface spin-polarization are invaluable for incorporation into devices that utilize spin-polarized currents. Point-contact Andreev reflection spectroscopy is currently one of the few techniques capable of direct measurement of surface spin-polarization. Niobium wire was electrochemically etched in a potassium hydroxide solution to form sharp tips which were used to form point-contacts with perovskite oxides in single crystal and thin film forms. Surface spin-polarization values were determined at 4.2 K for several materials including La$_{0.7}$Sr$_{0.3}$MnO$_{3}$, which is a material with purported 100{\%} spin polarization. The results show that surface spin polarization of perovskites is smaller than theoretically predicted.