Regioregular polythiophene based spintronic devices: effect of interface*

Polymeric spin valves have been fabricated using regio-regular (poly 3-hexylthiophene) (RRP3HT) as the spacer layer sandwiched between La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ (LSMO) and Co electrodes. The devices show high spin valve magnetoresistance (MR) at 5K (80{\%}) which reduces at room temperature to 1.5{\%}. The spin valve behavior is quite similar to a magnetic tunnel junction although the non-magnetic spacer layer ($\sim $100 nm) is much thicker than the tunneling limit. We attribute this behavior to the formation of a thin spin-selective tunneling interface between LSMO and RRP3HT caused by the chemical bonding between RRP3HT and LSMO as observed by x-ray photoelectron spectroscopy measurement. Deliberate destruction of the spin injecting interface by the introduction of a monolayer of organic insulators between LSMO and RRP3HT reduces the spin injection.