High temperature annealing treatment on Co doped ZnO bulks

Abstract

Zn0.95Co0.05O Bulk samples were synthesized by solid state reaction method and annealed by different processes. The Zn treated samples show ferromagnetism，whereas the vacuum annealed samples do not show ferromagnetism. The XRD patterns show that there is Co impurity phase in the sample after Zn treatment at 1100℃，which is the reason of the ferromagnetism observed. At low temperature，both the positive and negative magnetoresistance （MR） effect can be observed for all the samples. We conclude that the s-d exchange_interaction_induced spin-splitting gives rise to positive MR， while the formation of bound magnetic polarons and the magnetic field suppressed spin-disorder scattering are responsible for the negative MR behavior under high field.

The electrical transport behavior of Zn-treated Zn1−xMnxO bulks

“…As reported in our previous study on TM doped ZnO bulks, [13,30] the formation of BMPs is a universal phenomenon for ZnO based DMSs when the sample is in the localization range. The conduction mechanism and MR behavior of ferromagnetic Zn 1−x Co x O and paramagnetic Zn 1−x Mn x O bulks are very similar.…”

Influence of reducing anneal on the ferromagnetism in single crystalline Co-doped ZnO thin films

“…[10−20] However, the presented data were plagued by instability and a lack of reproducibility. In some cases, the ferromagnetism can be attributed to uncontrolled ferromagnetic clusters or secondary phases, [10,11] which is absent from single phase specimens. [12] However, in many other cases, hightemperature ferromagnetism could have been caused by defects, including Zn interstitials (Zn i ) and oxygen vacancies (V O ) which are presented in the TMdoped ZnO, as explained by the bound magnetic polaron (BMP) model.…”