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Magnetic Exchange-Coupling in CoPt/Co Bilayer thin Films

Published online by Cambridge University Press:  21 February 2011

J. Kim ,
K. Barmak ,
L. H. Lewis ,
D. C. Crewt  and
D. O. Welcht
J. Kim
Affiliation:
Dept. of Materials Science and Eng., Lehigh University, Bethlehem, PA 18015
K. Barmak
Affiliation:
Dept. of Materials Science and Eng., Carnegie Mellon University, Pittsburgh, PA 15213
L. H. Lewis
Affiliation:
Materials and Chemical Sciences Division, Dept. of Applied Sciences, Brookhaven National Laboratory, Upton, NY 11973
D. C. Crewt
Affiliation:
Materials and Chemical Sciences Division, Dept. of Applied Sciences, Brookhaven National Laboratory, Upton, NY 11973
D. O. Welcht
Affiliation:
Materials and Chemical Sciences Division, Dept. of Applied Sciences, Brookhaven National Laboratory, Upton, NY 11973
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Abstract

Thin film CoPt/Co bilayers have been prepared as a model system to investigate the relationship between microstructure and exchange coupling in two-phase hard/soft composite magnets. CoPt films, with a thickness of 25 nm, were sputter-deposited from a nearly equiatomic alloy target onto oxidized Si wafers. The films were subsequently annealed at 700°C and fully transformed from the FCC phase to the magnetically hard, ordered L1 0 phase. The coercivity of the films increased rapidly with annealing time until it reached a plateau at approximately 9.5 kOe. Fully-ordered CoPt films were then used as substrates for deposition of Co layers, with thicknesses in the range of 2.8-225 nm, in order to produce the hard/soft composite bilayers. As predicted by theory, the magnetic coherency between the soft Co phase and the hard, ordered CoPt phase decreased as the thickness of the soft phase increased. This decrease in coupling was clearly seen in the magnetic hysteresis loops of the bilayers. At small thicknesses of Co (a few nanometers), the shape of the loop was one of a uniform material showing no indication of the presence of two phases with extremely different coercivities. At larger Co thicknesses, constricted loops, i.e., ones showing the presence of a mixture of two ferromagnetic phases of different hardnesses, were obtained. The magnetic exchange present in the bilayer samples was qualitatively analyzed using magnetic recoil curves and the dependence of exchange coupling on the soft phase dimension in the bilayer hard/soft composite magnet films is discussed.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 577: Symposium H – Advanced Hard and Soft Magnetic Materials , 1999 , 353
Copyright
Copyright © Materials Research Society 1999

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References

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