Berlin 2008 – wissenschaftliches Programm
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HL: Fachverband Halbleiterphysik
HL 51: Poster IV
HL 51.38: Poster
Donnerstag, 28. Februar 2008, 16:30–19:00, Poster D
Magneto transport properties of codoped ZnCoO — •Christoph Knies1, Matthias T. Elm1, Jan Stehr1, Peter J. Klar1, Detlev M. Hofmann1, Tom Kammermeier2, Andreas Ney2, and Nikolai Romanov3 — 1I. Physikalisches Institut, Justus-Liebig Universität Giessen, Heinrich-Buff-Ring 16, D-35392 Giessen, Germany — 2Univ. Duisburg-Essen, Germany — 3Ioffe Institute, St. Petersburg, Russia
Current models predict that ZnO with ferromagnetic properties can be obtained by alloying the material with Co. Additionally a co-doping with shallow donors is needed to mediate the exchange interaction. We have prepared thin film of such materials by colloid chemical methods with Co concentrations up to 30%. For Co concentrations higher than 15 % the formation of secondary phases becomes evident from X-ray diffraction. All samples are high resistive in the as grown state and can be converted to n-type conduction by an annealing step in Zn vapour (450 °C, for 10 min.), which is believed to create Zn interstitial shallow donors. This process is reversible, subsequent annealing in air or O2 causes high resistivity again. The conducting films are suitable for temperature dependent magneto-transport measurement in order to investigate a possible spin-polarisation of carriers. We find the usual weak negative magneto-resistive effect in the ZnO reference sample. In the Co doped samples this effect is superimposed by a positive magneto-resistive effect at temperatures below 40 K. It is due to the alloy scattering caused by the Co ions. The results of further detailed characterisation of the co-doped ZnCoO will be discussed.