Effect of ion irradiation on the structural and the magnetic properties of Zn 0.75Co 0.25O magnetic semiconductors

Abstract

We have used magnetron co-sputtering to grow Zn 0.75Co 0.25O magnetic semiconductors on SiO 2/Si substrate at 400 °C. X-ray diffraction analysis has shown that the film is textured with c-axis of the wurtzite structure along the growth direction. Optical absorption measurements have been performed and showed three absorptions bands that are due to the transitions between the crystal-field-split 3 d levels of tetrahedral Co 2+ substituting Zn 2+ ions. Magnetization measurements have been performed at room temperature and have shown the presence of the ferromagnetism with a saturation magnetization of about 0.2 μ B / Co . Irradiation with He ions at 520 °C have been performed on the as-deposited film. For a dose of 6 × 10 16 cm −2 a huge increase of the magnetic moment up to 0.37 μ B / Co has been observed and accompanied with an improvement of the crystalline quality. However, for higher doses the magnetic moment is strongly reduced down to 0.13 μ B / Co . This is attributed to the change in the free carriers density in the ZnO host.