Electrochemical deposition of (Mn, Co)-codoped ZnO nanorod arrays without any template

(Mn,Co)-codoped ZnO nanorod arrays were successfully prepared on Cu substrates by electrochemical self-assembly in solution of 0.5 mol/l ZnCl2-0.01 mol/l MnCl2-0.01 mol/1 COCl2-0.1 m01/1 KCl-0.05 mol/l tartaric acid at a temperature of 90 degrees C, and these nanorods were found to be oriented in the c-axis direction with wurtzite structure. Energy dispersive X-ray spectroscopy and x-ray diffraction show that the dopants Mn and Co are incorporated into the wurtzite-structure of ZnO. The concentrations of the dopants, and the orientations and densities of nanorods can easily be well controlled by the current densities of deposition or salt concentrations. Magnetization measurement indicates that the prepared (Mn, Co)-codoped ZnO nanorods with a coercivity of about 91 Oe and a saturation magnetization (M-s) of about 0.23 emu/g. The anisotropic magnetism for the (Mn, Co)-codoped ZnO nanorod arrays prepared in solution of 0.5 mol/l ZnCl2-0.01 mol/l MnCl2-0.01 mol/l COCl2-0.1 mol/l KCl-0.05 mol/l tartaric acid with current density of 0.5 mA/cm(2) was also investigated, and the crossover where the magnetic easy axis switches from parallel to perpendicular occurs at a calculated time of about 112 min. The anisotropic magnetism, depending on the rod geometry and density, can be explained in terms of a competition between self-demagnetization and magnetostatic coupling among the nanorods. (C) 2007 Elsevier B.V. All rights reserved.