On the relationship of high coercivity and L1{sub 0} ordered phase in CoPt and FePt thin films

Journal Article · Fri Oct 01 04:00:00 EDT 1999 · Journal of Applied Physics

DOI:https://doi.org/10.1063/1.371397· OSTI ID:686516

Ristau, R A; Barmak, K ^[1]; Lewis, L H ^[2]; Coffey, K R; Howard, J K ^[3]

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1. Department of Materials Science and Engineering, Lehigh University, Bethlehem, Pennsylvania 18015 (United States)
2. Materials Science Division, Department of Applied Science, Brookhaven National Laboratory, Upton, New York 11973-5000 (United States)
3. IBM Storage Systems Division, 5600 Cottle Road, San Jose, California 95193 (United States)

The microstructure and the room-temperature hysteretic magnetic properties of sputtered, 10 nm thin films of equiatomic binary alloys of CoPt and FePt were characterized using transmission electron microscopy (TEM) and a superconducting quantum interference device (SQUID) magnetometer. A transformation from an atomically disordered, face-centered-cubic structure to the L1{sub 0} ordered structure occurred during postdeposition annealing and was characterized using digital analysis of dark-field 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 the SQUID magnetometer. In contrast to the relationship most commonly described in the literature, 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 for both CoPt and FePt. 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. {copyright} {ital 1999 American Institute of Physics.} thinsp

• OSTI ID: 686516
• Journal Information: Journal of Applied Physics, Journal Name: Journal of Applied Physics Journal Issue: 8 Vol. 86; ISSN JAPIAU; ISSN 0021-8979
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
ANNEALING
COBALT ALLOYS
COERCIVE FORCE
HYSTERESIS
IRON ALLOYS
MAGNETIC PROPERTIES
MICROSTRUCTURE
NUCLEATION
PERMANENT MAGNETS
PHASE TRANSFORMATIONS
PLATINUM ALLOYS
SQUID DEVICES
THIN FILMS
TRANSMISSION ELECTRON MICROSCOPY