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 600 °C. X-ray diffraction has shown that the films are epitaxied with the epitaxial relation Zn0.75Co0.25O(0 0 0 1) 〈101¯0〉//Al2O3(0 0 0 1)〈112¯0〉. The rocking curve of the 600 °C grown film has a 0.8° 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.