Regensburg 2007 – scientific programme

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MA: Fachverband Magnetismus

MA 10: Spinelectronics/Spininjection in Heterostructures

MA 10.6: Talk

Monday, March 26, 2007, 16:30–16:45, H23

Thermal phase transformation and perpendicular exchange coupling of Co nanocrystals embedded in ZnO — •Shengqiang Zhou, Kay Potzger, Wolfgang Skorupa, Manfred Helm, and Jürgen Fassbender — 1Institute of Ion Beam Physics and Materials Research, Forschungszentrum Dresden-Rossendorf, P.O. Box 510119, 01314 Dresden, Germany

Recently, due to the potential application in spintronics, ferromagnet-semiconductor hybrid structures have attracted huge attention [1]. Large magnetoresistance was observed in GaAs consisting MaAs nanocrystals and granular ZnO/Co systems [2, 3]. Wide-band-gap semiconductors (e.g. ZnO) doped with transition metals were reported to be diluted magnetic semiconductors with Curie temperatures above room temperature [4]. However, the origin of the observed ferromagnetism is still controversial. In this work, Co nanocrystals (NCs) were formed inside ZnO by ion implantation. The Co NCs are crystallorgraphically oriented inside ZnO. The magnetic properties, e.g. anisotropy and blocking temperature, can be tuned by annealing. In the as-implanted and annealed (823 K) samples, Co NCs have been found and show superparamagnetism. After annealing at 923 K, the sample exhibits a much higher blocking temperature and shows a perpendicular exchange bias effect. The semiconducting ZnO consisting of Co NCs could be a promising hybrid for spin-injection. 1.Ohno, Semicond. Sci. Technol. 17, 275 (2002). 2.Wellmann, et al., App. Phys. Lett. 73, 3291 (1998). 3.Pakhomov, et al., J. App. Phys. 95, 7393 (2004). 4.MacDonald, et al., Nat. Materials 4, 195 (2005).