November 24, 2010 Wednesday 15:30
Numan Akdoğan, Gebze Institute of Technology, Department of Physics Nanomagnetism and Spintronic Research Center (NASAM)
ZnO-based Diluted Magnetic Semiconductors for Spintronic Applications

Diluted magnetic semiconductors (DMS) are promising candidates for spintronic applications at ambient temperatures, provided that their Curie temperature (TC) is far enough above room temperature. Therefore, a number of different semiconductor hosts have been investigated to test their magnetic properties. In particular, the calculations of Dietl et al. [1] were the first to indicate that Mndoped ZnO could exhibit ferromagnetism above room temperature. Later, Sato et al. have also investigated ZnO-based DMS by ab initio electronic structure calculations and reported ferromagnetic ordering of 3d transition metal ions in ZnO [2]. These theoretical predictions initiated an outburst of experimental activities of TM-doped ZnO. Actually, some of these studies indeed claim ferromagnetic signals above room temperature. However, the origin of ferromagnetism in this system is still under debate. In this talk, I present a corresponding detailed study of the structural and magnetic properties of a Co-implanted ZnO film grown on a sapphire substrate. The structural data indicate a Co cluster formation in the sapphire substrate close to the ZnO/Al2O3 interface. However, no indication of clustering in the ZnO layer has been found. The XAS data with a multiplet structure around the Co L3 edge clearly shows that the implanted cobalt ions are in the Co2+ oxidation state in Co-implanted ZnO film. The magnetization measurements show that there are two magnetic phases in the Co-implanted ZnO/Al2O3 films. One is the ferromagnetic phase due to the Co substitution on Zn sites in the ZnO host matrix and the second magnetic phase originates from Co clusters in the sapphire substrate. Furthermore, we have found very high magnetic moment of 2.81 μB per substituted cobalt atom with a very high Curie temperature (TC>>400 K) in Co-implanted ZnO film [3]. The six-fold in-plane magnetic anisotropy of the FMR signal has been observed for the first time in ZnO-based diluted magnetic semiconductors is also a clear indication for long range ferromagnetic ordering between substitutional cobalt ions in the single-crystalline ZnO films [4]. [1] T. Dietl, H. Ohno, F. Matsukura, J. Cibert, and D. Ferrand, Science, 287, 1019 (2000). [2] K. Sato and H. Katayama-Yoshida, Jpn. J. Appl. Phys. 40, L334 (2001). [3] N. Akdoğan, A. Nefedov, K. Westerholt, H. Zabel, H. W. Becker, C. Somsen, R. Khaibullin, L. Tagirov, J. Phys. D: Appl. Phys. 41, 165001 (2008). [4] N. Akdoğan, B. Rameev, S. Güler, O. Öztürk, B. Aktaş, H. Zabel, R. Khaibullin, and L. Tagirov, Appl. Phys. Lett. 95, 102502 (2009).