New advances in organic spintronics

Abstract

The basic components of spintronic devices are spin polarized ferromagnets and spin transporting non-magnetic spacers. Exploiting carbon-based materials for these components promises to extend functionality of information storage and processing as well as to improve device integration and fabrication. Here we present the magnetoresistance of organic semiconductor rubrene (C 42H28) used as a spacer in La2/3Sr 1/3MnO3 (LSMO)/organic semiconductor (OSC)/Fe heterojunctions. Efficient spin polarized tunneling through the thin layer of rubrene spacer (5 nm) was observed. As the thickness of rubrene layers is increased, device current is strongly limited by carrier injection resulting in strong temperature dependent device resistance. The carrier injection is described with thermionic field emission at the metal/OSC interface. As a next step toward organic spintronics we used an organic based magnet vanadium-tetracyanoethylene (V(TCNE)x, x∼2) in tandem with LSMO in a spin- valve with 5 nm rubrene spacer. V(TCNE)x is the earliest developed room temperature molecule-based magnet (Tc ∼ 400 K). Due to strong on-site Coulomb interaction and weak intermolecule overlapping their magnetic state can be described with a model of half-semiconductor in which valence and conduction bands are spin polarized. The magnetoresistance data for bulk V(TCNE)x is in agreement with the model of spin polarized valence and conduction bands. We demonstrated that an organic-based magnetic semiconductor V(TCNE)x functions very well as an electron spin polarizer in the standard spintronic device geometry.