Mössbauer studies of dilute magnetic semiconductors (IS-443)
R. Mantovan1, M. Fanciulli1, H.P. Gunnlaugsson2, G.Weyer2, R. Sielemann3, D. Naidoo4, K. Bharuth-Ram5, S. Olafsson6, G. Langouche7, K. Johnston8
1Laboratorio Nazionale MDM CNR-INFM, Agrate Brianza (MI) 20041, Italy
2Department of Physics and Astronomy,University of Aarhus, DK-8000 Århus C, Denmark
3Hahn-Meitner Institute, 14109 Berlin, Germany
4School of Physics, University of the Witwatersrand, WITS 2050, South Africa
5School of Physics, University of KwaZulu-Natal, Durban 4041, South Africa
6Physics Department, Science Institute University of Iceland, Iceland
7Department of Physics, Katholike Universiteit, Leuven, Belgium
8EP Division, CERN, CH-1211 Geneva 23, Switzerland
The study of materials showing multifunctional properties at room temperature (RT) is a challenging task for material science and of importance for future applications in spin-based electronics. The prediction of a Curie temperature above RT in Mn-doped ZnO  started a new field of research, with the aim to investigate magnetism in normally non-magnetic oxides. Despite the enormous experimental and theoretical efforts, the origin of the magnetism in (3d-elements) doped and pure ZnO is still a matter of debate in the scientific community. Calculations showing a vacancy-driven mechanism for the magnetism in ZnO have been proposed [2, 3], but clear experimental evidences for such mechanisms are still lacking.
In the framework of the experiment IS-443 at ISOLDE-CERN, we apply Mössbauer spectroscopy to investigate the magnetic properties in ZnO upon implantation with radioactive 57Mn+ (T½ = 1.5 min), decaying to the 57mFe Mössbauer state (T½ = 100 ns). We study the electronic and magnetic configurations of Fe atoms in the ZnO crystals, and the interaction between the Mn/Fe atoms with the defects induced during the implantation process . Our results show that the majority of the Fe atoms are located on Zn sites in a high-spin Fe3+ state at 600 K, giving a strong magnetic contribution in ZnO. The formation/annealing of the magnetism in ZnO is interpreted as occurring/disappearing upon the association/dissociation of Mn/Fe complexes with the lattice defects created in the implantation process . We present an overview of our experimental findings focusing on the essential role played by the lattice defects in observing magnetism in ZnO.
 T. Dietl, H. Ohno, F. Matsukura, J. Cibert., and D. Ferrand, Science 287, 1019 (2000).
 N. A. Spaldin, Phys. Rev. B 69, 125201 (2004).
 A. Debernardi and M. Fanciulli, Appl. Phys. Lett. 90, 212510 (2007).
 G. Weyer, H.P. Gunnlaugsson, R. Mantovan, M. Fanciulli, D. Naidoo, K. Bharuth-Ram, T. Agne, J. Appl. Phys., in print.