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The new paradigm of electronics, 'spintronics', promises to extend the functionality of information storage and processing in conventional electronics. The principal spintronics device, the 'spin valve', consists of two magnetic layers decoupled by a spin-transporting spacer, which allows parallel (on) and antiparallel (off) alignment of the magnetizations (spins) of the two magnetic layers. The device resistance then depends on the spin alignment controlled by the external magnetic field. In pursuit of semiconductor spintronics, there have been intensive efforts devoted to develop room-temperature magnetic semiconductors and also to incorporate both inorganic semiconductors and carbon-based materials as the spin-transporting channels. Molecule/organic-based magnets, which allow chemical tuning of electronic and magnetic properties, are a promising new class of magnetic materials for future spintronic applications. Here, we report the realization of an organic-based magnet as an electron spin polarizer in the standard spintronics device geometry. A thin non-magnetic organic semiconductor layer and an epitaxial ferromagnetic oxide film were employed to form a hybrid magnetic tunnel junction. The results demonstrate the spin-polarizing nature of the organic-based magnetic semiconductor, vanadium(TCNE: tetracyanoethylene)(x) (x approximately 2; T(c) approximately 400 K), and its function as a spin injector/detector in hybrid magnetic multilayer devices.

We report that organic semiconductors such as -sexithiophene (-6T) have magnetoresistance (MR) with unexpected sign changes; depending on applied voltage, temperature, and layer thickness, the resistance may either increase or decrease upon application of a small magnetic field (<100 mT). We propose that MR and the inversion of MR are due to the role of hyperfine interaction in a magnetic field, as illustrated by the recombination-limited regime.

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