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

L. PEREIRA, E.L MUÑOZ, A.W. CARBONARI, M. CORDEIRO, M. MERCURIO, M. RENTERÍA, R. SAXENA, AND J. J. MESTNIK-FILHO

Ginebra

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

Executive Committee del 3th HFI/NQI International Conference

The investigation on wide-band gap semiconductors doped with transition metals (TM)has attracted a considerable interest in last years, mostly because of its possibleapplications in the spintronic field. Among these materials, cobalt-doped zinc oxide(Co-doped ZnO) has been one of the most investigated systems. Despite the focus onthe magnetic aspect in these compounds in order to reach ferromagnetic ordering atroom temperature, there is still enough space for some interesting questionsregarding electronic structure that might be investigated. The study of the possiblechanges in the electronic structure caused by the introduction of a TM, is a questionof great interest, especially if it is necessary to introduce large quantities of TMand carriers. One of the quantities that can be used in order to observe thedifferences in the electronic structure of a given crystalline site, is the electricfield gradient (EFG), since it is a very sensitive parameter that may reveal even smallchanges occurring in an atomic scale. In this way, in the reference [1] it ispresented PAC results at 111Cd probe inserted in pure ZnO and 5% Co-doped ZnO. Twomeasurements on pure compound were performed; one with a commercially availablesample and the other one was prepared at our laboratory together with the Co-dopedsample utilizing sol-gel methodology. It was observed that the perturbation spectraare practically identical for all of the three situations, with Cd quadrupolefrequency (nuq) assuming values within the 31-32 MHz range. Yet in another work [2],it was developed a systematic PAC study with the 111Cd probe focusing on theconcentration variation of cobalt dopant in ZnO within the 5 – 15 % Co range. Thesesamples have a single ZnS-type phase and presented a same major fraction of siteswith a very similar quadrupole frequency nuq in the range between 31.1 – 33.1 MHz.In the present work we try to explain which electronic phenomena could be occurringwhen Co-doped ZnO do not generate any change at Cd efg. For this purpose we usedfirst principles electronic structure calculations, carried out within the DensityFunctional Theory (DFT) framework using Linearized Augment Plane Waves methods (LAPW)embodied at the WIEN2k code [3]. In our calculations, several ZnO cells were set upwith Cd and/or Co ions and then, different Cd neighborhoods were simulated. Theelectric field gradient at Cd, the density of states (DOS) and charge densitydistributions were analyzed. The resulted EFG at Cd are in agreement with theexperimental values [2]. By means of DOS it was observed that both the Co and Znelectronic structure are very similar. References [1] M.E. Mercurio, A.W. Carbonariet al., J. Magn. Magn. Mater. 322, 1195 (2010). [2] M.E. Mercurio, A.W. Carbonari,oral communication. To be published. [3] Blaha, P., Schwarz et al: WIEN2K, anAugmented Plane Wave plus Local Orbitals… . Karlheinz Schwarz, Techn. UniversitätWien, Austria. ISBN 3-9501031-1-2 (2001).