1. Department of Physics, University of Utah, Salt Lake City, Utah 84112, USA

Correspondence to: Jing Shi Email: jshi@physics.utah.edu

A spin valve is a layered structure of magnetic and non-magnetic (spacer) materials whose electrical resistance depends on the spin state of electrons passing through the device and so can be controlled by an external magnetic field. The discoveries of giant magnetoresistance¹ and tunnelling magnetoresistance² in metallic spin valves have revolutionized applications such as magnetic recording and memory, and launched the new field of spin electronics³—'spintronics'. Intense research efforts are now devoted to extending these spin-dependent effects to semiconductor materials. But while there have been noteworthy advances in spin injection and detection using inorganic semiconductors^{4, 5, 6}, spin-valve devices with semiconducting spacers have not yet been demonstrated. -conjugated organic semiconductors may offer a promising alternative approach to semiconductor spintronics, by virtue of their relatively strong electron–phonon coupling⁷ and large spin coherence⁸. Here we report the injection, transport and detection of spin-polarized carriers using an organic semiconductor as the spacer layer in a spin-valve structure, yielding low-temperature giant magnetoresistance effects as large as 40 per cent.

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