Effect of annealing on magnetic exchange coupling in CoPt/Co bilayer thin films
- Department of Materials Science and Engineering, Lehigh University, Bethlehem, Pennsylvania 18015 (United States)
- Department of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213 (United States)
- Materials and Chemical Sciences Division, Department of Applied Sciences, Brookhaven National Laboratory, Upton, New York 11973 (United States)
Thin film CoPt/Co bilayers have been prepared as a model system to investigate the relationship between microstructure and exchange coupling in two-phase nanocomposite permanent magnets. The bilayers were prepared by magnetron sputter deposition of near-equiatomic CoPt with a thickness of 25 nm onto oxidized Si wafers. In the as-deposited state, CoPt had the A1 (fcc) structure and was magnetically soft. Before reinsertion into the sputtering chamber for the deposition of 2.8-16.7 nm thick Co layers, the CoPt films were annealed at 700 degree sign C for 120 min to produce the magnetically hard, fully ordered L1{sub 0} phase. The presence of exchange coupling in the bilayers was verified by magnetic hysteresis and recoil measurements and showed that only for Co thicknesses below 6.3 nm was this layer (in its as-deposited state) coupled through its full thickness to the CoPt layer. Annealing the bilayer samples at 300 and 550 degree sign C for 20 min resulted in improvement of the interlayer magnetic coupling and produced clear differences in the magnetic reversal coherency and the recoil curves. However, for some samples, the improved coupling resulted in a decrease in coercivity, indicating that there is an optimum in the coupling strength for the attainment of high coercivity. Transmission electron microscopy studies of the bilayers in plan view showed that the increased interlayer coupling with annealing was a result of improved granular epitaxy of Co to CoPt. (c) 2000 American Institute of Physics.
- OSTI ID:
- 20216265
- Journal Information:
- Journal of Applied Physics, Vol. 87, Issue 9; Other Information: PBD: 1 May 2000; ISSN 0021-8979
- Country of Publication:
- United States
- Language:
- English
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