Magnetization processes in Co Cu multilayers with low magnetoresistive hysteresis

We have used transmission electron microscopy to study magnetization processes in Co/Cu multilayers with the Cu spacer layer thickness close to 9 Angstrom. The films show giant magnetoresistance (GMR) values approximate to 25%, saturation fields of 1-2 kOe, and very little magnetoresistive hysteresis; they are of interest as position sensors. While the Cu thickness was chosen to correspond to the first antiferromagnetic maximum, magnetic images taken throughout a magnetization cycle attest to the fact that the antiferromagnetic coupling is far from complete. Detailed analysis of image sequences and the corresponding low angle diffraction patterns suggests that the coupling is dominated by a biquadratic component. This is consistent with the relatively low value of GMR. Furthermore, the well-defined and relatively simple domain processes which are observed over the low field regime (+/-50 Oe) explain why little hysteresis is observed. (C) 1999 American Institute of Physics. [S0021-8979(99)05412-2].