Structural and magnetic properties of transition metals doped ZnO(TM)/ZnO multilayers

摘要

ZnO(Fe)/ZnO multilayers (MLs) with Fe 6.5% (Fe-doped sample) and ZnO(FeNi)/ZnO MLs with Fe_(22)Ni_(78) 6.5% (Ni-doped sample) prepared by helicon plasma sputtering were investigated. Structures of as-prepared Fe- and Ni-doped samples show the layer structures and the ZnO crystalline structures. However, the samples annealed at 773 K induced the formation of ZnFe_2O_4 for Fe doped sample, and the growth of metallic Ni for Ni-doped sample. Furthermore, Fe atoms in the annealed Fe-doped sample are dispersed mainly in the surface region, and Ni atoms in as-prepared and annealed Ni-doped samples are located uniformly in the film. The ionic states of Fe in Fe-doped sample and Ni in Ni-doped sample before and after annealing are the mixed Fe~(2+/3+) and metallic Ni, respectively. Therefore, it is considered that the as-prepared and the annealed Ni-doped samples form Ni particles. As-prepared samples showed the paramagnetic properties. However, the magnetic state of the as-prepared Ni-doped sample is partly superparamagnetic due to the existence of small Ni particles. On the other hand, annealed samples show the ferromagnetic characteristics due to formation of ZnFe_2O_4 for Fe-doped ones and growing metallic Ni particles for Ni-doped ones.