Defect mediated reversible ferromagnetism in Co and Mn doped zinc oxide epitaxial films
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 0.08 μB/Co and 0.05 μB/Mn, much lower than 3.0 μB/Co and 5.0 μB/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.
Document Details
- Document Type
- Pub Defense Publication
- Publication Date
- Dec 01, 2012
- Source ID
- 10.1063/1.4768721
Entities
People
- J. T. Prater
- Jagdish Narayan
- Siddhartha Mal
- Sudhakar Nori
- Suhrit Mula
Organizations
- Army Research Office
- Maulana Azad National Institute of Technology, Bhopal
- National Science Foundation
- North Carolina State University
- United States Army Research Laboratory