Magnetoresistance properties of granular nanowires composed of carbon nanoparticles embedded in a Co matrix

Spin-dependent transport was studied in granular nanowires composed of magnetic and nonmagnetic nanoparticles embedded in a Co matrix. At low temperature, giant magnetoresistance (GMR) and tunnelinglike magnetoresistance (TMR) appear. GMR and TMR-like magnetoresistance are identified by the temperature and bias voltage dependence of the resistivity and the temperature dependence of the magnetoresistance. Electron microscopy observations suggest also that the percolation threshold of the particles in the wire triggers the transition from diffusive to hopping transport. The magnetoresistance behavior is very similar for both Ohmic and non-Ohmic transport. The origin of the magnetoresistance is ascribed to the presence of constrained magnetic walls pinned between the nanoparticles.