Skip navigation
Please use this identifier to cite or link to this item: http://repository.iitr.ac.in/handle/123456789/12671
Title: Defect mediated reversible ferromagnetism in Co and Mn doped zinc oxide epitaxial films
Authors: Mal S.
Nori S.
Mula, Suhrit
Narayan J.
Prater J.T.
Published in: Journal of Applied Physics
Abstract: 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 0.08μB/Co and 0.05μB/ Mn, much lower than 3.0μB/Co and 5.0μB/Mn, indicating the prominent role of intrinsic defects in RTFM with some contribution from Co2+-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. © 2012 American Institute of Physics.
Citation: Journal of Applied Physics (2012), 112(11): -
URI: https://doi.org/10.1063/1.4768721
http://repository.iitr.ac.in/handle/123456789/12671
Issue Date: 2012
ISSN: 218979
Author Scopus IDs: 36160564100
6701754734
12783902100
35415849700
7007016412
Author Affiliations: Mal, S., Department of Material Science and Engineering, North Carolina State University, Raleigh, NC 27695, United States
Nori, S., Department of Material Science and Engineering, North Carolina State University, Raleigh, NC 27695, United States
Mula, S., Department of Material Science and Engineering, North Carolina State University, Raleigh, NC 27695, United States, Department of Metallurgical and Materials Engineering, National Institute of Technology, Rourkela 769008, India
Narayan, J., Department of Material Science and Engineering, North Carolina State University, Raleigh, NC 27695, United States
Prater, J.T., Materials Science Division, Army Research Office, Research Triangle Park, NC 27709, United States
Funding Details: The authors were pleased to acknowledge the support of the Army Research Office under Grant W911NF-04-D-0003, and the National Science Foundation under Grant NSF 0653722. FIG. 1. XRD (θ-2θ) scans of the undoped ZnO and Zn 0.7 TM 0.3 O (TM = Co and Mn) films grown at substrate temperature of 550 °C and oxygen partial pressure of 10 −5 Torr. FIG. 2. XRD plots of thermal annealed and laser irradiated Zn 0.95 Co 0.05 O (a) and Zn 0.95 Mn 0.05 O (b) films. FIG. 3. UV–Vis transmission spectra of Co doped ZnO films. FIG. 4. UV–Vis transmission spectra of Mn doped ZnO films. FIG. 5. Plots of (αhν) 2 versus hν for the Co doped ZnO films. Straight line fits through the linear regions of the plot are extrapolated to hν = 0 to find the bandgap. FIG. 6. Plots of (αhν) 2 versus hν for the Mn doped ZnO films. FIG. 7. Plot of the bandgap values as a function of dopant concentration. FIG. 8. Room temperature hysteresis loops of Zn 0.95 Co 0.05 O films grown at different conditions. FIG. 9. Room temperature hysteresis loops of oxygen annealed, oxygen annealed followed by vacuum annealed and oxygen annealed followed by laser irradiated Zn 0.95 Co 0.05 O films. FIG. 10. Room temperature hysteresis loops of oxygen annealed, oxygen annealed followed by vacuum annealed and oxygen annealed followed by laser irradiated Zn 0.95 Co 0.05 O films.
Corresponding Author: Mal, S.; Department of Material Science and Engineering, North Carolina State University, Raleigh, NC 27695, United States; email: smal@ncsu.edu
Appears in Collections:Journal Publications [MT]

Files in This Item:
There are no files associated with this item.
Show full item record


Items in Repository are protected by copyright, with all rights reserved, unless otherwise indicated.