Absence of ferromagnetism in V-implanted ZnO single crystals.pdf

1 Absence of ferromagnetism in V-implanted ZnO single crystals Shengqiang Zhou*, K. Potzger, H. Reuther, K. Kuepper, W. Skorupa, M. Helm, and J. Fassbender Institute for Ion Beam Physics and Materials Research, Forschungszentrum Rossendorf, POB 510119, 01314 Dresden, Germany * Electronic mail: s.zhou@fz-rossendorf.de 2 Abstract The structural and magnetic properties of V doped ZnO are presented. V ions were introduced into hydrothermal ZnO single crystals by ion implantation with fluences of 1.2×1016 to 6×1016 cm-2. Post-implantation annealing was performed in high vacuum from 823 K to 1023 K. The ZnO host material still partly remains in a crystalline state after irradiation, and is partly recovered by annealing. The V ions show a thermal mobility as revealed by depth profile Auger electron spectroscopy. Synchrotron radiation x-ray diffraction revealed no secondary phase formation which indicates the substitution of V onto Zn site. However in all samples no pronounced ferromagnetism was observed down to 5 K by a superconducting quantum interference device magnetometer. 3 I. Introduction Diluted magnetic semiconductors (DMS) have recently attracted huge research attention because of their potential application for spintronics devices [1]. In DMS materials, transition or rare earth metal ions are substituted onto cation sites of the host semiconductor and are coupled with free carriers to yield ferromagnetism via indirect interaction [1, 2]. ZnO doped with V was found to be ferromagnetic at room temperature [3]. However, the origin of the observed ferromagnetism in transition metal doped ZnO is still controversial, e.g. ferromagnetic clusters [4], or extrinsic reasons (substrate impurities [5], use of stainless-steel tweezers [6]). The absence of ferromagnetism has been reported for Mn, Co doped ZnO [7]. Therefore, the observation of ferromagnetism in V doped ZnO should be carefully