Synthesis and characterization of Ni-doped ZnO: A transparent magnetic semiconductor

We report synthesis of a transparent magnetic semiconductor by incorporating Ni in zinc oxide (ZnO) matrix. ZnO and nickel-doped zinc oxide (ZnO: Ni) thin films (similar to 60 nm) are prepared by fast atom beam (FAB) sputtering. Both undoped and doped films show the presence of ZnO phase only. The Ni concentration ( in at%) as determined by energy dispersive X-ray (EDX) technique is similar to 12 +/- 2%. Magnetisation measurement using a SQUID magnetometer shows that the Ni-doped films are ferromagnetic, having coercivity (H(c)) values 192, 310 and 100 Oe and saturation magnetization (M(s)) values of 6.22, 5.32 and 4.73 emu/g at 5, 15 and 300 K, respectively. The Ni-doped film is transparent (> 80%) across visible wavelength range. Resistivity of the ZnO: Ni film is similar to 2.5 x 10(-3) Omega cm, which is almost two orders of magnitude lower than the resistivity (similar to 4.5 x 10(-1) Omega cm) of its undoped counterpart. Impurity d-band splitting is considered to be the cause of increase in conductivity. Interaction between free charges generated by doping and localized d spins of Ni is discussed as the reason for ferromagnetism in the ZnO: Ni film. (C) 2008 Elsevier B.V. All rights reserved.