’Invisible’ ferromagnetic secondary phases in Co doped ZnO

The search for ferromagnetic transition-metal doped ZnO, i.e., diluted magnetic semiconductors (DMS), has turned into the search for unwanted secondary phases by high-resolution structural analysis [1]. Such phases even can lead to anomalous Hall effect arising from charge carrier spin polarization. In this talk we show that the general analysis technique for the identification, i.e. x-ray diffraction spectroscopy, fails to identify a recently observed kind of ferromagnetic inclusions with heavy crystalline disorder. We discuss the properties of those clusters using the popular Co:ZnO system.
[1] K. Potzger, S. Q. Zhou, H. Reuther, A. Mucklich, F. Eichhorn, N. Schell, W. Skorupa, M. Helm, J. Fassbender, T. Herrmannsdorfer, T. P. Papageorgiou, Appl. Phys. Lett. 88, 052508 (2006).