Dresden 2011 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 37: Magnetic Semiconductors II
MA 37.4: Vortrag
Mittwoch, 16. März 2011, 15:30–15:45, HSZ 401
muSR proof of magnetism in undoped ZnO thin films — •Thomas Tietze1, Patrick Audehm1, Boris Straumal1,2, Peter Straumal2, Zaher Salman3, Hubertus Lütkens3, Thomas Prokscha3, and Eberhard Goering1 — 1Max-Planck-Institut für Metallforschung, Heisenbergstr. 3, D-70569 Stuttgart — 2Moscow Institute of Steel and Alloys, Technological University, Leninsky Prospect 4, 119991 Moscow, Russia — 3Paul Scherrer Institut, Labor für Myon-Spin Spektroskopie, CH-5232 Villigen PSI, Switzerland
Over the last decade tremendous efforts have been taken to reveal the origin of room temperature (RT) ferromagnetism (FM) in transition metal (TM) doped ZnO. SQUID measurements mostly showed ferromagnetic behavior whereas element specific methods like x-ray magnetic circular dichroism (XMCD) could not address the FM to any of the containing elements. FM occurred even in undoped ZnO, if the specific grain boundary area exceeds a threshold value. We suggest vacancy like states located at the grain boundaries as a possible source of the origin of RT FM of undoped ZnO. In order to proof intrinsic magnetism of nanostructured pure ZnO, we performed low energy muon spin rotation (LE-muSR) experiments at the Swiss Muon Source (SmuS). SQUID hysteresis loops revealed enhanced FM according to higher specific grain boundary area, in perfect agreement with our muSR measurements. The maximum muSR related magnetic volume fraction for nano grained samples was about 35%, while the pure ZnO single crystal sample was solely diamagnetic. Therefore, we present intrinsic evidence for a new type of RT-FM.