Dynamic hyperfine interactions in 111In/111Cd-doped ZnO semiconductor: PAC results supported by ab initio calculations

E.L. MUÑOZ, M.E. MERCURIO, L.F.D. PEREIRA, M.R. CORDEIRO, A.W. CARBONARI, AND M. RENTERÍA.

Buenos Aires

Workshop; FCM2010, International Workshop "At the Frontiers of Condensed Matter Physics V"; 2010

CAC-CNEA

During the last 25 years, dynamic hyperfine interactions have been observed in several Time-Differential  gamma-gamma Perturbed- Angular-Correlation (PAC) experiments when the probe isotope 111Cd, obtained after the electron-capture (EC) decay of its parent 111In, was used in certain semiconducting and insulator oxides. These dynamic interactions are originated in the electronic relaxation of the probe atom, usually called after-effects (AE), which follows the EC decay of the 111In isotope.This relaxation must occur during the life time of the intermediate-sensitive-nuclear state of the gamma-gamma cascade, time-windowin which we measure the hyperne interaction at the probe nucleus with external elds by means of the PAC technique. Upto now it was believed that the ECAE can only be detected if the probe atom was a non-isovalent impurity in the systemunder study.Following these ideas, we present here results of PAC experiments performed in an oxide, ZnO, were the 111Cd probe atomis an isovalent impurity. But this time the observed behavior will be analyzed enlighten by recent ab initio calculations ofthe electric-field gradients (EFG) as a function of the charge state of the Cd atom.PAC experiments carried out on 111In-diffused polycrystalline ZnO have been performed in order to measure the EFG at(111In (EC)-->)111Cd nuclei located at the cation site of the ZnO crystal structure. The PAC experiments were performedin the temperature range 77 K-1075 K. The presence of dynamic hyperfine interactions with low intensity was observed,fitting the spectra with a perturbation factor based in the Bäverstam and Othaz model [U. Bäverstam et al., Nucl. Phys.A 186, 500 (1972)]. The experimental results were compared with ab initio calculations performed with the Full-PotentialAugmented Plane Wave plus local orbital (FP-APW+lo) method, in the framework of the Density Functional Theory (DFT),using the Wien2K code. The dependence of the EFG at the Cd sites as a function of the charge state of the supercell wasdetermined. From this ab initio-experimental comparison we can correlate the strength dynamic hyperfine interaction withthe dependence of the EFG on the charge state of the impurity Cd atom.