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Concentration and Defect Dependent Ferromagnetism above Room Temperature in Co Doped ZnO Films Prepared by Metalorganic Decomposition

Published online by Cambridge University Press:  01 February 2011

P. Kharel
Affiliation:
C. Sudakar
Affiliation:
G. Lawes
Affiliation:
R. Suryanarayanan
Affiliation:
R. Naik
Affiliation:
V. M. Naik
Affiliation:
[email protected], University of Michigan-Dearborn, Department of Natural Sciences, United States
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Abstract

Zn1−xCoxO (x = 0.0 – 0.047) thin films (thickness ∼0.5 – 1 μm) have been prepared on sapphire substrates using metalorganic decomposition (MOD) method. The X-ray diffraction and Raman scattering studies indicate films to be polycrystalline ZnO with wurtzite structure. The optical absorption spectra show an expected bandgap of ∼3.2 eV. The magnetization studies show that the as prepared films lack the room temperature ferromagnetic order, whereas the films when vacuum annealed at a temperature 500 – 600 °C acquire ferromagnetic ordering at room temperature. Further, the observed ferromagnetism (FM) appears only for a limited range of Co concentration, 0.03 < x < 0.10 (after heat treating in vacuum at 550 °C), and it reversibly disappears upon re-annealing in air. The data presented here seem to suggest that the appearance of ferromagnetic order is dictated by both the oxygen defects and the critical concentration of Co, and thus may lend support to a recent model proposed by Coey et al. [Nature Materials4, 173 (2005)].

Type
Research Article
Copyright
Copyright © Materials Research Society 2006

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References

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