Direct observation of asymmetric magnetization reversal in Fe/Cr/Fe thin films

We report our experimental finding showing that there exists an asymmetric magnetization reversal behavior along the direction normal to the easy axis in Fe/Cr/Fe thin films. Interestingly enough, the magnetoresistance and the Kerr hysteresis loops are found to be quite asymmetric between the decreasing- and the increasing-field branches of the loop in the applied-field direction normal to the easy axis whereas they are found to be symmetric in the direction parallel to the easy axis. To clarify the microscopic details of the asymmetric magnetization reversal, we use a magneto-optical microscope magnetometer to carry out a direct time-resolved observation of the domain evolution patterns at each switching field. The magnetization reversal is revealed to take place with a fast, abrupt, simple 180-degree domain-wall configuration at the switching field in the increasing-field branch while it is found to take place with an irregular and complex configuration at the switching field in the decreasing-field branch.