Domain structure during magnetization reversal of PtMn/CoFe exchange bias micro-patterned lines

The magnetic domain configuration and the magnetization reversal behavior of micropatterned exchange bias elements were investigated by means of magnetic force microscopy. In addition to the unidirectional anisotropy the shape anisotropy determines the overall magnetization reversal behavior. In order to modify the ratio between both anisotropy contributions the exchange bias field strength was reduced by means of 5 keV He+ ion irradiation. For the as-prepared samples a mono-domain magnetization state with the magnetization direction aligned along the exchange bias field direction was found regardless of the element shape. After irradiation the unidirectional anisotropy contribution is reduced and hence the previously homogeneous magnetization state brakes up into small domains with 360° domain walls in between. The appearance of these domain walls, which was mainly observed for the descending branch of the magnetization reversal, is found to depend strongly on the structure width and orientation.