Size effects on the magnetization reversal behavior of exchange bias modulated thin films

Thin films of NiFe/IrMn/Ta with spatially modulated unidirectional anisotropy have been prepared by local oxidation of the antiferromagnetic IrMn layer. Varying the lateral dimensions and orientation of the stripe structures with respect to the direction of exchange bias, the films exhibited different magnetization reversal behavior. While stripes aligned parallel to the unidirectional anisotropy direction display a two-step hysteresis loop, those with perpendicular orientation show a single-step, shifted hysteresis loop. Magnetic domain observation reveals separate switching of the magnetically different stripes for the parallel structures. For decreased lateral dimensions as well as perpendicularly aligned stripes quasidomain states are observed. The different magnetization reversal phenomena are discussed in terms of direct exchange coupling of the bimodal magnetic properties at the stripe interfaces.