Summary: Journal of Magnetism and Magnetic Materials 267 (2003) 191196
Exchange bias effects in ferromagnetic wires
M.K. Husain, A.O. Adeyeye*, C.C. Wang, V. Ng, T.S. Low
Information Storage Materials Laboratory, Department of Electrical and Computer Engineering, National University of Singapore,
4 Engineering Drive 3, Singapore 117576, Singapore
Received 11 February 2003; received in revised form 18 March 2003
We have investigated the exchange bias effect in micron-sized ferromagnetic wires made from Co and Ni80Fe20 films.
The wires were fabricated using optical lithography, metallization by sputtering and lift-off technique. Magnetotran-
sport measurements were performed at temperatures ranging from 3 to 300 K. We observed marked changes in the
magnetoresistance (MR) properties as the temperature is varied. At 300 K, the field at which the sharp peak occurs
corresponding to the magnetization reversal of the Co wires is 167 Oe and is symmetrical about the origin. As the
temperature was decreased to 3 K, we observed a shift in the peak positions of the MR characteristics for both
the forward and reverse field sweeps corresponding to a loop shift of 582 Oe in the field axis. The asymmetric shift in the
MR loops at low temperatures clearly indicates the exchange bias between ferromagnetic (Co) and antiferromagnetic
parts (Co-oxide at the surfaces) from natural oxidation. Ni80Fe20 wires of the same geometry showed similar effect with
a low exchange bias field. The onset of exchange biasing effect is found to be 70 and 15 K for the Co and Ni80Fe20 wires,
respectively. A striking effect is the existence of exchange biasing effect from the sidewalls of the wires even when the
wires were capped with Au film.
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