Magnetic perpendicular anisotropy in sputtered (Zn0.75Co0.25)O dilute magnetic semiconductor

We have used reactive magnetron co-sputtering to grow Zn0.75CO0.25O dilute magnetic semiconductor on Al2O3(0 0 0 1) substrates at 400 and 600degreesC. X-ray diffraction has shown that the films are epitaxied with the epitaxial relation Zn0.75CO0.25O(0 0 0 1) <1 0 1 0>//Al2O3(0 0 0 1)<1 1 (2) over bar 0>. The rocking curve of the 600degreesC grown film has a 0.8degrees FWHM indicating a good structural quality of the film. For both films, we observe a ferromagnetic hysteresis loop at low and room temperature. This is consistent with the thermal variation of the magnetic susceptibility, which shows that the ferromagnetism is present for a temperature as high as 300 K. In addition, magnetization loops recorded at 10 K with the magnetic field along and perpendicular to the film plane evidence a perpendicular magnetic anisotropy with the easy magnetization axis along the growth axis. The origin of the ferromagnetism in these films is ascribed to the CO2+ atoms from structural, magnetic, and optical transmission measurements. (C) 2004 Published by Elsevier B.V.