'Local structure and magnetism of Cu-doped ZnO pellets investigated at the Cu K-edge XAS and XMCD: experiment and theory'
| Autor: | P. S. Vachhani, O. Sipr, R.K. Ramamoorthy, G. Dalba, F. Rocca, J. Vackar, A.K. Bhatnagar |
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| Rok vydání: | 2012 |
| Předmět: | |
| Zdroj: | XAFS15-15th International Conference for X-ray Absorption Fine Structure, Beijing, China, 22-28/07/2012 info:cnr-pdr/source/autori:P. S. Vachhani, O. Sipr, R.K. Ramamoorthy, G. Dalba, F. Rocca, J. Vackar, A.K. Bhatnagar/congresso_nome:XAFS15-15th International Conference for X-ray Absorption Fine Structure/congresso_luogo:Beijing, China/congresso_data:22-28%2F07%2F2012/anno:2012/pagina_da:/pagina_a:/intervallo_pagine |
| Popis: | Magnetism of w-ZnO doped by transition metal atoms is an intriguing phenomenon which evades a consistent explanation. Reliable and consistent information on the local structure and local magnetic properties around the dopant is therefore very desirable. EXAFS, XANES and XMCD analysis done at the same edge is expected to be a very useful tool in this respect. Our study focuses on polycrystalline Cu-doped ZnO pellets, synthesized with Cu concentration varying from 2 to 10 weight percents by solid state reaction. Structural characterizations were carried out by x-ray diffraction and by EXAFS and XANES spectroscopies at the Cu K-edge. Magnetic properties were measured globally using a SQUID magnetometer and locally by relying on the Cu K-edge XMCD. At low Cu content, most of the Cu atoms substitute Zn in the ZnO wurtzite lattice while, for the higher Cu concentrations, Cu starts to segregate as CuO. XMCD measurements show that local moments at the Cu atoms behave paramagnetically. The calculations demonstrate that the measured XMCD signal indeed corresponds to magnetic Cu atoms in substitutional sites. We also investigated theoretically the effect of oxygen vacancies on the XANES and on the XMCD and find that the effect on the XANES is not very large while the XMCD signal changes considerably. Calculation also predicts that the replacement of Zn atoms by Cu atoms cannot be seen in the XAS, which is consistent with our experimental data. |
| Databáze: | OpenAIRE |
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