Berlin 2008 – scientific programme
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MA: Fachverband Magnetismus
MA 3: Magnetic Semiconductors
MA 3.6: Talk
Monday, February 25, 2008, 11:30–11:45, H 1012
Ferromagnetism and magnetic clusters in cobalt-doped ZnO — Matthias Opel1, Karl-Wilhelm Nielsen1, Sebastian Bauer1, •Sebastian T. B. Goennenwein1, Rudolf Gross1, Júlio C. Cezar2, Dieter Schmeisser3, Jürgen Simon4, and Werner Mader4 — 1Walther-Meißner-Institut, Bayerische Akademie der Wissenschaften, Garching, Germany — 2European Synchrotron Radiation Facility, Grenoble, France — 3Angewandte Physik II, Brandenburgische Technische Universität Cottbus, Germany — 4Institut für Anorganische Chemie, Rheinische Friedrich-Wilhelms-Universität Bonn, Germany
Ferromagnetic semiconductors (FMS) - i.e. semiconductors exhibiting long-range magnetic ordering - are intriguing materials. However, in spite of intensive research in the last decade, the existence of homogeneous FMS with a Curie temperature around or above room temperature still is controversial. A particularly tedious issue are local sample inhomogeneities or magnetic clusters, which can yield strong magnetic signals resembling the behaviour expected for a homogeneous FMS. Using pulsed laser deposition, we have grown cobalt-doped ZnO films on single crystalline ZnO substrates. Combining x-ray magnetic circular dichroism, DC magnetometry, and AC susceptibility measurements with a detailed structural analysis by high resolution x-ray diffraction, transmission electron microscopy, and electron-spectroscopic imaging, we can unambigously trace the characteristic, ferromagnetic-like behaviour of our ZnO:Co samples at room-temperature to nanometer-sized superparamagnetic metallic cobalt precipitates.