Contact induced magnetism in carbon nanotubes

Evidence is presented to show that carbon nanotubes can become magnetized when they are in contact with magnetic material. Spin-polarized charge transfer at the interface between a flat ferromagnetic metal substrate and a multiwalled carbon nanotube leads to a spin transfer of about 0.1 mu(B) per contact carbon atom. The corresponding magnetization is detected by using magnetic force microscopy to probe the stray field in the neighbourhood of the nanotube. Magnetic contrast is observed for carbon nanotubes placed on cobalt or magnetite substrates, but it is absent on silicon, copper or gold substrates. This observation of contact-induced magnetism opens a new avenue for implementing spin-electronics at the molecular level, where the current leads can be separated from the electrodes producing spin polarization.