Enhanced spin-valve effect in magnetically doped carbon nanotubes

Spin valves made of nanotubes contacted to magnetic electrodes may display significant values of magnetoresistance but are limited by the restricted capacity for spin injection into the tube and by the unwanted spin-flip scattering caused by magnetic impurities. We propose an alternative route to produce the spin-valve effect which (a) does not involve magnetic electrodes, avoiding the spin injection limitation, and (b) uses magnetically coupled impurities to generate an efficient spin filter that enhances the magnetoresistance by orders of magnitude. Furthermore, we predict that substitutional Mn impurities on metallic nanotubes will generate enormously large values of magnetoresistance.