Defect-mediated room temperature ferromagnetism in zinc oxide

We have introduced systematic changes in the electrical, magnetic and optical properties of undoped ZnO films through irradiation with an UV Excimer laser. Increases in the electrical conductivity and magnetic moment have been controlled precisely with the number of laser pulses, without altering the Wurtzite crystal structure and nn-type semiconducting characteristics of the films. The laser induced ferromagnetism and concomitant conductivity enhancement can be reversed through subsequent thermal annealing. Hence, we have successfully demonstrated reversible switching of RTFM in undoped ZnO by employing oxygen annealing (off) and laser irradiation (on). We discuss these findings in terms of defects and defect complexes created by pulsed laser irradiation.