Magnetic and optical properties of Co-doped ZnO nanorod arrays

In this study, Zn 1−x Co x O nanorod arrays were deposited on Si substrates by magnetron sputtering followed by the hydrothermal method at 100 °C. The effects of doping concentration and hydrothermal growth conditions on the crystal structures, morphologies, magnetic and optical properties of the obtained Zn 1−x Co x O nanorod arrays were studied. Surface characterization showed Zn 1−x Co x O nanorod arrays with uniform and dense distributions along the [0001] direction with the hexagonal wurtzite structure. Besides, no impurity phases were detected in Zn 1−x Co x O nanorod arrays. The room-temperature ferromagnetism of Zn 1−x Co x O nanorod arrays was detected based upon the high-saturation magnetization of 4.4 × 10 –4 emu/g, the residual magnetization of 1.1 × 10 –4 emu/g and the coercive field of 309 Oe. Furthermore, the photoluminescence (PL) spectra exhibited by the Zn 1−x Co x O nanorod arrays with the luminescence intensity in the ultraviolet region were nearly five times that of the pure ZnO nanorod arrays. With the increase in the Co 2+ doping concentration, the redshift in the ultraviolet emission peaks was observed. The theoretical results presented obvious spin polarization near the Fermi level, with strong Co 3d and O 2p hybridization effects. The magnetic moments were mainly generated by Co 3d and partial contribution of O 2p orbital electrons. These results indicated that Zn 1−x Co x O nanorod arrays can be used as potential magneto-optical materials.