In this work, we investigate the effects of cobalt doping on the structural, magnetic and transport properties of half metallic Fe3O4 films fabricated on MgO (100) substrates by co-sputtering. The doped films exhibit a highly broadened metal-insulator Verwey transition as compared to that of undoped Fe3O4 films. The magnetic and transport properties of the doped films are markedly sensitive to the Co doping concentration; films with high Co doping exhibit almost negligible coercivity at room temperature. Magnetoresistance (MR) curves show linear magnetic field dependence for the undoped films, while a reduction in MR and departure from linear field dependence is observed for Co-doped films. (c) 2005 Elsevier B.V. All rights reserved.