Organic spintronics: The case of Fe/Alq3/Co spin-valve devices

We have embarked on studying magneto-transport response of organic spin-valves made of evaporated Alq3 spacer sandwiched between two ferromagnetic (FM) electrodes with spin-injecting capability. Recently, we have fabricated and completed studies on organic spin-valve devices using half-metallic manganites as one of the spin-injecting FM electrode, which have shown giant magnetoresistance (GMR) of up to 40% at 11 K. Also we found that the GMR response decreases at higher temperatures, and actually disappears at temperatures above ∼180 K, partially because the FM manganite loses its magnetic properties at ambient temperature. In order to realize room temperature organic spin-valve devices, we have begun studying spin-valve devices where both spin-injecting FM electrodes have high Curie temperatures, and thus maintain their magnetic properties at ambient temperature. In this paper we report our preliminary investigations of Fe/Alq3/Co spin-valves, where both electrodes are regular, d-band metallic FM's. We found that these devices show GMR with maximum of about 5% at 11 K. However, at elevated temperatures the GMR value steeply decreases, and in fact vanishes at 90 K. We attribute this decrease to the increase of the spin-lattice relaxation rate of the injected spin-1/2 carriers in the Alq3 spacer at elevated temperatures, where there is also change in the spin carrier injection mechanism at the Fe/Alq3 interface.