Microstructures And Magnetism Of Cr, Fe Doped ZnO And Fe, Cu-codoped ZnO Diluted Magnetic Semiconductors

In this paper, Cr, Fe doped ZnO and Fe, Cu-codoped ZnO diluted magnetic semiconductors powders and films were successfully prepared by solid-state reaction and plused laser deposition, respectively. The effect of transition metal concentration and preparation conditions on their microstructures and magnetic properties were systematically investigated. The preparation conditions include sintering atmosphere, sintering temperature, and deposition atmosphere. And the origin of the ferromagnetism and the mechanism were discussed. Conclusions presented in this paper can be summarized as follows: (1) In Zn1-xCrxO (x=2~20) powders, no secondary phases were detected within the sensitivity of x-ray diffraction (XRD) when the Cr concentration is 2 at. % and 5 at. %. And the appearance of the ZnCr2O4 impurity phase in the ZnO: Cr 10 at. % was an indication that the solubility limit of Cr in ZnO had been exceeded. The Zn1-xCrxO powders exhibit no ferromagnetism, whether they are sintered in air or annealed in vacuum. The powders sintered in air was then pressed into a pellet, then it was sintered. The resulting pellet was used as the target in a pulsed laser deposition (PLD) chamber. All the ZnCrO films deposited by PLD exhibit room temperature ferromagnetism. With the increase of Cr concentration, Ms of the films is initially increased, and then reduced, which may be related with the formation of different Cr-O-Cr or Cr-O-Zn-O-Cr, due to Cr ions substituting different Zn ions in ZnO. (2) In Zn0.97Fe0.03O powders, the high sintering temperature is beneficial to enhance the solubility of Fe in ZnO. When the sintering temperature is 800℃, Fe can be absolutely dissolved in ZnO host, and the mono-phasic Zn0.97Fe0.03O powders was obtained. The ferromagnetism of ZnO powders was enhanced due to the introduction the defects of oxygen vancancies, which was generated by the annealing process in oxygen deficiency atmosphere of vacuum. Moreover, The optimal ferromagnetism was obtained at the annealing temperature of 575℃. (3) Fe, Cu-codoped ZnO powders sintered in air or vacuum exhibit no ferromagnetism; (4) All Fe-doped ZnO and Fe, Cu-doped ZnO films are mono-phasic. No Fe-doped ZnO films show ferromagnetism. However, Fe, Cu-doped ZnO films exhibit ferromagnetism, which may be associated with both the additional doping of Cu and the generation of donor defects of oxygen vacancies. To sum up, although different doping elements were chosen, the different preparation methods and various preparation conditions were used, and the corresponding different Ms was obtained, there are similarities among them. Both ZnCrO and ZnFeO powders sintered in air show no ferromagnetism. And both ZnCrO and ZnFeCuO films exhibit ferromagnetism. Moreover, their Ms is strongly dependent on the doping concentration and the deposition atmosphere. Therefore, both the substitution of doping elements for Zn in ZnO and the generation of the defects are two key factors in inducing magnetic ordering of ZnO-based diluted magnetic semiconductors.