Dresden 2009 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 24: Magnetic Semiconductors
MA 24.1: Vortrag
Mittwoch, 25. März 2009, 14:45–15:00, HSZ 401
Element specific structural and magnetic properties of Co-doped ZnO - from a paramagnet to a superparamagnetic ensemble — •Katharina Ollefs1, Shuangli Ye1, Verena Ney1, Tom Kammermeier1, Fabrice Wilhelm2, Andrei Rogalev2, and Andreas Ney1 — 1Fachbereich Physik, Universität Duisburg-Essen, Duisburg, Germany — 2ESRF, Grenoble, France
The structural and magnetic properties of the dilute magnetic semiconductor (DMS) Co:ZnO prepared by reactive magnetron sputtering were studied using hard x-ray synchrotron radiation. By means of x-ray linear dichroism (XLD) measurements and respective simulations using the FDMNES code [1] the local crystallographic structure was investigated. For Co:ZnO with optimized growth conditions the local environment for both Co and Zn is the wurtzite structure of the ZnO bulk material. Virtually all Co dopant atoms are incorporated on cation lattice sites like previously shown for pulsed laser deposited samples [2]. X-ray magnetic circular dichroism (XMCD) and the corresponding element specific hysteresis at the Co K-edge reveal pure paramagnetic behavior as corroborated by SQUID measurements. Altered preparation conditions lead to the onset of phase-separation as revealed by a clear reduction of the XLD signal. With the onset of clustering a superparamagnetic blocking behavior arises which is typical for a particle ensemble. Changes in magnetic and electronic properties of such an ensemble due to annealing effects will be discussed.
[1] Y. Joly, Phys. Rev. B 63, 125120 (2001)
[2] A. Ney et al., Phys. Rev. Lett. 100, 157201 (2008)