Richard A. Fry(a), R. D. McMichael(a), J. E. Bonevicha, P. J. Chen(a), W. F. Egelhoff, Jr.(a), and C.-G. Lee(b)
(a)National Institute of Standards and Technology, Gaithersburg, MD  20899  USA
(b)Changwon National University, Changwon, Kyingnam, 641-773 Korea

It has recently been found that large uniaxial anisotropy fields in excess of 120 kA/m (1500 Oe) can be
created in thin (3 nm to 5 nm) films of Co by obliquely sputtered Ta underlayers.  This anisotropy can be
used to pin the bottom film of a spin valve while having only a modest effect on the top 'free' film,
separated by a 2.5 nm Cu spacer layer.  We describe measurements of magnetic anisotropy and thermal
stability in these Ta-pinned spin valves.  Using room temperature giant magnetoresistance (GMR) as a
measure, we find that the structure is stable under cumulative 20 min anneals at 25°C intervals up to
300°C; GMR decreases to zero upon further anneals up to 450°C.  Measurements taken at elevated
temperatures reveal that GMR decreases linearly with temperature, extrapolating to zero at
approximately 425°C, while the anisotropy field is much less temperature dependent, remaining nearly
constant up to 150°C and gradually decreasing to 50 % of its room temperature value at 325°C.  The
thermal stability of the large uniaxial anisotropy is comparable to that of the exchange bias in NiMn
pinned films.