Study of electronic structure and electric field gradient at Cd probe in Co-doped ZnO matrix by first principles calculations

L.F.D. PEREIRA; E. L. MUÑOZ; A. W. CARBONARI; M. CORDEIRO; M. MERCURIO; M. RENTERÍA; J. MESTNIK-FILHO

CERN, Ginebra, Suiza.

Conferencia; HFI/NQI2010, 15th International Conference on Hyperfine Interactions & 19th International Symposium on Nuclear Quadrupole Interaction; 2010

Comité organizador de la Conferencia

The investigation on wide-band gap semiconductors doped with transition metals (TM) has attracted a considerable interest in last years, mostly because of its possible applications in the spintronics field. Among these materials, cobalt-doped zinc oxide (Co-doped ZnO) has been one of the most investigated systems. Despite the focus on the magnetic aspect in these compounds – in order to reach ferromagnetic ordering at room temperature -, there is still enough space for some interesting questions regarding electronic structure that might be investigated.The study about the possible changes in the electronic structure caused by the introduction of a TM, is a question of great interest, once it is necessary to introduce sufficient quantities of TM and carriers. One of the great tools that can be used in order to observe the differences in the electronic structure of a given crystalline site, is the electric field gradient (EFG), which is a very sensible parameter, that may reveal even small changes occurring in an atomic scale. In this way, the reference [1] presents PAC results at 111Cd probe inserted in pure ZnO (obtained commercially and prepared by sol-gel methodology) and 5% Co-doped ZnO (by sol-gel method), in which perturbation spectra are practically identical for the three situations, with Cd quadrupole frequency (íq) assuming values in 31-32 MHz range. In another work [2], it was developed a systematic study, for samples prepared by sol-gel method with 111Cd PACprobe, focusing on the concentration variation of cobalt dopant in ZnO, where PAC measurements of the samples with 5 –15 % Co range (which these samples have a single phase ZnS-type) showed the same major fraction corresponding to Zn site with íq values very similar for all samples, in the range between 31.1 –33.1 MHz. Here we tried to explain what electronic phenomena could be occurring when Co-doped ZnO do not generate any change at Cd efg. For make this propose we used first principles calculations, which were developed inside the Density Functional Theory (DFT) framework using Linearized Augment Plane Waves methods (LAPW) embodied at the WIEN2k  code [3]. In our calculations several ZnO cell were set up with Cd and/or Co ions, so different Cd neighborhoods were simulated. Cadmium efg, density of state (DOS) and density of charge were analyzed. Cadmium efg results are in agreement with experimental values [2]. By means of DOS was observed that Co and Zn electronic structure could be similar. References [1] M.E. Mercurio, A.W. Carbonari et al., J. Magn. Magn. Mater. 322, 1195 (2010). [2] M.E. Mercurio, A.W. Carbonari, oral communication. To be published. [3] Blaha, P., Schwarz, K., Madsen, G.K.H., Kvasnicka, D., Luitz, J.: WIEN2K, an Augmented Plane Wave plus Local Orbitals Program for Calculating Cristal Properties. Karlheinz Schwarz, Techn. Universitat Wien, Austria. ISBN 3-9501031-1-2 (2001).