Magnetic and transport properties of (Mn, Co)-codoped ZnO films prepared by radio-frequency magnetron cosputtering

(Mn, Co)-codoped ZnO films have been synthesized on c-sapphire (0001) by a radio-frequency magnetron sputtering system in which two targets were sputtered together. X-ray-diffraction measurements indicate that the films are highly c-axis oriented. X-ray photon spectra show that the doped Mn and Co ions in (Mn, Co) ZnO films are both in the divalent states. The films show ferromagnetic behavior with a coercivity of about 90 Oe and a saturation moment of 0.11 mu(B)/(0.3Mn(2+)+0.7Co(2+)) at 300 K. In the lower temperatures between 5 and 20 K, a relatively large positive magnetoresistance over 10% was observed for (Mn-0.03, Co-0.07)Zn0.90O film. The number of carrier concentration is experimentally established to be 1.5613x10(18) cm(-3) and the mobility to be 2.815 cm(2) V-1 s(-1) for (Mn-0.03, Co-0.07)Zn0.90O film by Hall measurements at 300 K. The origins of the room-temperature magnetism and the large positive magnetoresistance are also discussed. (c) 2005 American Institute of Physics.