by: Prof. Gillian Gehring
       (Department of Physics and Astronomy, University of Sheffield)

    Abstract

    Much work is done on magnetically doped ZnO; after reviewing the field briefly the talk will address two issues:
    How does the magnetism depend on the carrier density and how may this be understood?
    What can be learned about the position of the energy levels of the transition metal ions Co and Mn, relative to the ZnO bands by the way in which doping changes the carrier concentration and the mobility and how is this related to magnetism?
    The Sheffield group makes films of ZnO doped with Al and with Co or Mn using PLD. The principle methods of characterisation are electrical resistivity and Hall effect and also magneto-optics and optical absorption. The principle results are that the magnetism can by large in both the insulating and metallic range and small between – confirming the results from Tsinghua University. We also find the magneto-optic signals and the Hall mobilities are rather different for Co and Mn doping.
    The implications of these results are discussed.