Defect mediated reversible ferromagnetism in Co and Mn doped zinc oxide epitaxial films

Journal Article · Sat Dec 01 00:00:00 EST 2012 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.4768721· OSTI ID:22089609

Mal, Siddhartha; Nori, Sudhakar; Narayan, J. ^[1]; Mula, Suhrit ^[1]; Prater, J. T. ^[2]

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1. Department of Material Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695 (United States)
2. Materials Science Division, Army Research Office, Research Triangle Park, North Carolina 27709 (United States)

We have introduced defects in ZnO (undoped and doped with Co and Mn) epitaxial thin films using laser irradiation from nanosecond laser pulses and thermal annealing in oxygen ambient. In contrast to the as grown samples, the laser irradiated films show a significant increase in conductivity, enhancement in UV emission, while maintaining the same wurtzite crystal structure. Room-temperature ferromagnetism (RTFM) is observed in laser-irradiated samples, which increased with the number of laser pulses up to a certain value where magnetic moment saturates. The induced ferromagnetism as well as the enhanced electrical conductivity can be reversed with thermal annealing in oxygen ambient. The magnetization in Co and Mn doped films was found to be strong function of growth conditions and defect concentration. X-ray diffraction and optical absorption experiments suggested a 2+ valance state and tetrahedral coordination for both Co and Mn ions. There is a simultaneous increase in n-type electrical conductivity with the number of laser pulses and continue to exhibit semiconducting behavior in both undoped and doped films. The saturation magnetization was found to be 0.08 {mu}{sub B}/Co and 0.05 {mu}{sub B}/Mn, much lower than 3.0 {mu}{sub B}/Co and 5.0 {mu}{sub B}/Mn, indicating the prominent role of intrinsic defects in RTFM with some contribution from Co{sup 2+}-oxygen vacancy complexes. We propose a unified mechanism based upon introduction of intrinsic defects to explain RTFM and n-type conductivity enhancements during pulsed laser and thermal annealing.

• OSTI ID: 22089609
• Journal Information: Journal of Applied Physics, Vol. 112, Issue 11; Other Information: (c) 2012 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA); ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
36 MATERIALS SCIENCE
ANNEALING
COBALT ADDITIONS
CRYSTAL DEFECTS
DOPED MATERIALS
ELECTRIC CONDUCTIVITY
EPITAXY
FERROMAGNETIC MATERIALS
FERROMAGNETISM
LASER RADIATION
LAYERS
MAGNETIC MOMENTS
MAGNETIZATION
MANGANESE ADDITIONS
SEMICONDUCTOR MATERIALS
TEMPERATURE RANGE 0273-0400 K
THIN FILMS
VACANCIES
X-RAY DIFFRACTION
ZINC OXIDES