Planar-type spin valves based on low-molecular-weight organic materials with La0.67Sr0.33MnO3 electrodes

The spin injection and transport properties of low-molecular-weight organic semiconductors such as pentacene and bis(l,2,5-thiadiazolo)-p-quinobis(l,3-dithiole) (BTQBT) were investigated utilizing planar-type spin-valve devices with half-metallic La0.67Sr0.33MnO3 electrodes. The devices showed clear spin-valve characteristics with a magnetoresistance (MR) ratio of up to 29% at 5K. The MR ratio was found to depend on the gap spacing of the electrodes, the applied bias voltage, temperature, and the crystallinity of the films. It was also affected by gas adsorption onto the films, indicating that the spins were scattered by carriers and/or radical ions in the films generated through charge transfer from gas molecules.