Comment on 'Exchange penetration and anisotropy magnetoresistance in Co-Nimultilayers'

In this comment we show how the claim of Hernando et al (1998 J. Phys. D: A ppl. Phys. 31 637) of an enhanced magnetoresistance of 130% with a field se nsitivity of 6%/Oe in Co/Ni sputtered multilayers is based on a misinterpre tation of the magnetoresistance effect. To illustrate this we use their squ are four-point probe arrangement to obtain a magnetoresistance effect of 17 6% with a field sensitivity of 11.7%/Oe in a sputtered permalloy film. We p resent critical analysis of this 'extraordinary' effect showing that the hi gh magnetoresistance values obtained are not intrinsic to the material but are an artefact of the measurement method.