Manipulating ferromagnetism of ZnO-based diluted magnetic semiconductors via transition metal atoms inhomogeneous distribution*

H. Xu, W. Hao
Beihang University, CN

Keywords: Zn0.95Co0.05O and Zn0.98Mn0.02O nanocrystals, ferromagnetism, inhomogeneous distribution

Summary:

The inhomogeneous distribution of transition metal (TM) ions is a general state in ZnO Diluted magnetic semiconductors (DMSs), it has important effects on the magnetism properties. The inhomogeneous TM distribution in ZDMSs explains why the magnetic properties can be well modulated by various surface treatments. Zn0.95Co0.05O and Zn0.98Mn0.02O nanocrystals were synthesized by the wet chemical route and were treated in different atmosphere. The environment around Co, Mn and the defect type and concentration were characterized by photoluminescence, Raman, X-ray photoelectron spectroscopy and X-ray absorption fine structure. It is found that the ferromagnetisms of the H2-annealed and Ar-annealed Zn0.95Co0.05O nanocrystals increase significantly, but that of the O2-annealed sample decreases. For Zn0.98Mn0.02O nanocrystals, our results indicate that Mn ions are prior to enter into the interstitial sites in ZnO and form Mn3+O6 octahedron coordination in the as-prepared samples. Antiferromagnetic coupling between neighboring Mn3+O6 can be observed in as-prepared samples. After H2 annealing, Mn3+ transfer to Mn2+ and substitute for Zn2+ to form Mn2+O4 tetrahedron coordination. The samples exhibit both ferromagnetic and antiferromagnetic behaviors. Our results indicate that inhomogeneous TM distribution is helpful for manipulating the states of the TM ions and the ferromagnetic coupling in ZnO-DMSs by post-treatment.