1. Department of Materials Science, University of Cambridge, Pembroke Street, Cambridge CB2 3QZ, UK
   
2. Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK
   
3. Institut de Ciencia de Materials de Barcelona, CSIC Campus UAB, 08193 Bellaterra, Barcelona, Spain
   
4. Cavendish Laboratory, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0HE, UK
   
5. Nanoscience Centre, University of Cambridge, JJ Thomson Avenue, Cambridge CB3 0FF, UK
   
6. Unité Mixte de Physique CNRS-Thales, TRT, 91767 Palaiseau and Université Paris-Sud, 91405 Orsay, France
   
7. Present addresses: ISMN-CNR, via Gobetti 101, 40129 Bologna, Italy (L.E.H.); Department of Physics, University of California, Berkeley, California 94720, USA (J.M.P.); Departamento de Física, Comisión Nacional de Energia Atómica, Gral. Paz 1499, 1650 San Martín, Buenos Aires, Argentina (V.F.); School of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK (G.B.).

Correspondence to: Neil D. Mathur¹ Correspondence and requests for materials should be addressed to N.D.M. (Email: ndm12@cam.ac.uk).

Spin electronics (spintronics) exploits the magnetic nature of electrons, and this principle is commercially applied in, for example, the spin valves of disk-drive read heads. There is currently widespread interest in developing new types of spintronic devices based on industrially relevant semiconductors, in which a spin-polarized current flows through a lateral channel between a spin-polarized source and drain^{1, 2}. However, the transformation of spin information into large electrical signals is limited by spin relaxation, so that the magnetoresistive signals are below 1% (ref. 2). Here we report large magnetoresistance effects (61% at 5 K), which correspond to large output signals (65 mV), in devices where the non-magnetic channel is a multiwall carbon nanotube that spans a 1.5 m gap between epitaxial electrodes of the highly spin polarized^{3, 4} manganite La_0.7Sr_0.3MnO₃. This spintronic system combines a number of favourable properties that enable this performance; the long spin lifetime in nanotubes due to the small spin–orbit coupling of carbon; the high Fermi velocity in nanotubes that limits the carrier dwell time; the high spin polarization in the manganite electrodes, which remains high right up to the manganite–nanotube interface; and the resistance of the interfacial barrier for spin injection. We support these conclusions regarding the interface using density functional theory calculations. The success of our experiments with such chemically and geometrically different materials should inspire new avenues in materials selection for future spintronics applications.