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Effect of codopants (Li, Na and K) on the magnetic properties of Co doped ZnO thin films |
| Ramasubramanian Swaminathan , Kumar Janakiraman |
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Crystal Growth Centre, Anna University, Chennai, Chennai 600025, India |
| Abstract |
| Zinc oxide (ZnO) is studied for a variety of electrical and optical applications because of its wide band gap, transparency and its high exciton binding energy (60 meV) [1]. Since the last decade, considerable work has been devoted in realizing ZnO as a Dilute Magnetic Semiconductor (DMS) by doping transition (TM) metals in it. Among the TM ions, Cobalt doping is one of the most investigated and is considered to yield high magnetic moment in ZnO [2].The nature of the observed magnetism in Co doped ZnO is not being clear as it is intrinsic or because of the presence of metallic cluster. The presence of defects or impurities are also affects the magnetic property in the Co doped ZnO. In this work, we report the study on the impact of I group codopants (Li, Na and K) on the magnetic properties of the Co doped ZnO thin films. CoyZn1-yO, LixCoyZn1-x-yO, NaxCoyZn1-x-yO and KxCoyZn1-x-yO (x, y =0.03) thin films were grown on sapphire (0001) substrates using Sol-gel spin coating technique. Sol-gel technique has been adapted inorder to realize the homogeneous and atomic scale doping in the films. Structural properties of the films were analyzed using X-ray diffraction. Raman scattering techniques indicated the substitution of the dopants in the ZnO matrix.The amount of incorporated K+ ions in the KxCoyZn1-x-yO films was found to be minimal. Surface morphology of the films was found to be of densely packed grains of varied sizes between 120 – 150 nm. The introduction of codopants was resultant in reducing the average grain sizes in the grown films. The transmittance spectra of all the films showed the characteristic Co2+ absorptions in the visible region at the wavelengths of 567, 619 and 673 nm. The optical bandgap energies of Co doped ZnO, (Li, Co) codoped ZnO, (Na, Co) codoped ZnO and (K, Co) codoped ZnO films were estimated to be 3.24 eV, 3.2 eV, 3.27 eV and 3.26 eV respectively. Photoluminescence measurement demonstrated the distinct variations in the nature of the intrinsic defects (Vo, Zni, Vzn
) in the different codoped ZnO films. Magnetic measurements showed the observation of the room temperature ferromagnetism in all the films. The magnetic moments found to be varied with the amount of incorporated Co in the grown films. Magnetic force microscopy was used to analyze the magneitc regions on the surfaces of the films. Presence of small metallic clusters of Co were observed along the grain boundaries. Figure 1 shows MFM images of Co doped ZnO. The introduction of Li and Na as codopants found to significantly reduced the amount of metallic cobalt in the grains. Our studies showed the nature of magnetism observed in the Co doped ZnO films could get changed by the use of codpants.
 Figure 1: MFM image of the Li,Co codoped film over scan area of 1000 nm × 1000 nm. References: 1. U. Ozgur, Ya. I. Alivov, C. Liu, A. Teke, M. A. Reshchikov, S. Dogan, V. Avrutin, S.J. Cho, and H. Morkoc, J. Appl. Phys. 98, (2005) 041301 2. M. Venkatesan, C. B. Fitzgerald, J. G. Lunney and J. M. D. Coey, Phys. Rev. Lett. 93 (2004) 177206. |
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Presentation: Poster at 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17, Topical Session 2, by Kumar JanakiramanSee On-line Journal of 17th International Conference on Crystal Growth and Epitaxy - ICCGE-17 Submitted: 2013-03-29 11:26 Revised: 2013-07-17 23:05 |