Magneto-Transport Studies Of Fe/Alq3/Co Organic Spin-Valves

Abstract

We have studied vertical organic spin‐valves made of evaporated π‐conjugated molecule, namely 8‐hydroxy‐quinoline aluminum (Alq3) semiconductor spacer sandwiched between two ferromagnetic (FM) electrodes with spin injecting capability. Recently we have communicated on our work with organic spin‐valve devices using half‐metallic manganites as one of the spin injecting FM electrode that showed giant magnetoresistance (GMR) of about 40% at 11 K. However, we found that the GMR decreases at high temperatures and actually disappears at 300 K, partially because the FM manganite loses its magnetic properties at ambient temperature. To realize room temperature organic spin‐valve devices, in the present work we report on our investigations of Fe/Alq3/Co spin‐valve devices, where both spin‐injecting FM electrodes (Fe and Co) have high Curie temperatures and thus maintain their magnetic properties at ambient temperature. We found that these devices show GMR of about 5% at 11K. However at elevated temperatures the GMR value steeply decreases, and in fact vanishes at 90K. We attribute this decrease to the increase of the spin relaxation rate of the injected carriers in the Alq3 organic spacer at elevated temperatures, and the carrier injection across the Fe/Alq3 interface that is dominated by thermo‐ionic emission at high temperatures.