Ferromagnetism and Crossover of Positive Magnetoresistance to Negative Magnetoresistance in Na-Doped ZnO

Na doped ZnO films were fabricated via a hydrothermal process. The films have shown room; temperature ferromagnetism and p-type conductivity. Crossover of positive to negative magnetoresistance has been observed with the variation of Na doping concentrations. The positive MR is due to pp exchange interaction induced Zeeman splitting to suppress the hopping path of holes. The ferromagnetism is attributed to the formation of a Zn vacancy complex. The negative magnetoresistance is due to the minimization of spin-dependent scattering by the applied magnetic field.