Asymmetric magnetic reversal of perpendicular exchange biased (Co∕Pt)5∕IrMn probed by magnetoresistance and magnetic force microscopy

Magnetic reversal of (Co∕Pt)5∕IrMn multilayers with perpendicular exchange bias has been studied by magnetoresistance and magnetic force microscopy (MFM). It has been found that as a function of perpendicular external field, the resistance decreases with field above saturation and has sharp maxima at the reversal fields due to the domain wall resistance effect. The latter contribution has been found to be asymmetric, suggesting a corresponding asymmetry in the domain state in the two branches of the hysteresis loop. This asymmetry correlates with the fractal dimension of the domain wall projection deduced from MFM images, which is larger on the descending branch of the hysteresis loop than along the ascending branch. This in turn can be explained as due to the different intensities of domain wall nucleation in the two branches.