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A Study on High Coercivity and L10Ordered Phase in CoPt and FePt Thin Films

Published online by Cambridge University Press:  21 February 2011

R. A. Ristau ,
K. Barmak ,
L. H. Lewis ,
K. R. Coffey  and
J. K. Howard
R. A. Ristau
Affiliation:
Department of Materials Science and Engineering, Lehigh University, Bethlehem, PA 18015
K. Barmak
Affiliation:
Department of Materials Science and Engineering, Lehigh University, Bethlehem, PA 18015
L. H. Lewis
Affiliation:
Materials Science Division, Department of Applied Science, Brookhaven National Laboratory, Upton, NY 11973-5000
K. R. Coffey
Affiliation:
IBM Storage Systems Division, 5600 Cottle Road, San Jose, CA 95193
J. K. Howard
Affiliation:
IBM Storage Systems Division, 5600 Cottle Road, San Jose, CA 95193
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Abstract

This study relates the microstructure of equiatomic binary alloys of CoPt and FePt with their room-temperature hysteretic magnetic properties, particularly their high coercivity. A transformation from an atomically disordered, face-centered-cubic structure to the Li0 ordered structure occurred during post-deposition annealing and was characterized using digital analysis of dark-field transmission electron microscopy (TEM) images. The transformation was observed to follow first-order nucleation and growth kinetics, and the ordered volume fraction transformed was quantified at numerous points during the transformation. The ordered volume fraction was then compared to the magnetic coercivity data obtained from a superconducting quantum interference device (SQUID) magnetometer. Although the relationship most commonly described in the literature is that the highest coercivity corresponds to a two phase ordered/disordered mixture, the maximum value for coercivity in this study was found to correspond to the fully ordered state. Furthermore, in samples that were less than fully ordered, a direct relationship between ordered volume fraction and coercivity was observed. The proposed mechanism for the high coercivity in these films is an increasing density of magnetic domain wall pinning sites concurrent with an increasing fraction of ordered phase.

Type
Research Article
Information
MRS Online Proceedings Library (OPL) , Volume 577: Symposium H – Advanced Hard and Soft Magnetic Materials , 1999 , 347
Copyright
Copyright © Materials Research Society 1999

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References

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