Magnetic and transport properties of Co-doped Fe3O4 films

We present a systematic study of the structural, magnetic, and magnetotransport properties of Co-doped Fe3O4 films deposited on MgO (100) substrates by cosputtering technique. Transmission electron microscopy images suggest that the undoped and Co-doped Fe3O4 films are polycrystalline in nature and consist of a well defined grain boundary network. The temperature dependence of resistance also shows that the transport mechanism in our films is dominated by electron tunneling across antiferromagnetically coupled grain boundaries. We observed that the magnetic properties of the doped films are markedly sensitive to the Co doping concentration, with the magnetization curves showing drastic changes in coercivity with increasing doping concentration. In-plane magnetoresistance curves show linear magnetic field dependence for the undoped Fe3O4 films while a reduction in magnetoresistance and a departure from linear field dependence are observed for the Co-doped films. (c) 2007 American Institute of Physics.