Electro- and magneto-transport properties of amorphous carbon films doped with iron

Electro- and magneto-transport properties of amorphous carbon films doped with iron element have been systematically studied. The electro-transport mechanism of the films is dominated by thermal activation at T > 200 K, Mott-type variable range hopping (VRH) at 200 K > T > 60 K and Efros-Shklovskii type (ES-) VRH at T < 60 K. An anomalous giant positive magnetoresistance (MR) 6.40% is found at the ES-VRH range, which is attributed to the spin blockage effect. At high temperatures, an anomalous Hall effect (AHE) is also found with a large AHE coefficiency 49.6 mu Omega cm/T. Electron energy loss spectroscopy (EELS) reveals that iron atoms chemically bond with carbon matrix. These iron carbides exist as amorphous nanoparticles with a diameter of 6-12 nm, which is regarded as the origin of the MR and AHE. Besides, the films are p-type conductive at high temperature, which might be related with the iron doping. These properties make iron doped amorphous carbon films applicable in carbon-based solar cells, magnetic sensors or some other multifunctional devices. (C) 2010 Elsevier B.V. All rights reserved.