Magnetization reversal asymmetry in (Co/Pt)/CoFe/IrMn multilayers with enhanced perpendicular exchange bias

The magnetization reversal of perpendicular exchange biased [Co/Pt]/Co60Fe40/IrMn and [Co/Pt]/Co/IrMn multilayers was investigated by time-resolved surface magneto-optical Kerr effect and Kerr microscopy. Compared with the nearly symmetric reversal of the [Co/Pt]/Co/IrMn with a smaller exchange bias field, significantly asymmetric domain evolution in the [Co/Pt]/Co60Fe40/IrMn with a larger exchange bias field was directly observed by Kerr microscopy. The asymmetric magnetization reversal is discussed in terms of the average thermally activated energy barriers as well as the dispersions of the barriers. The substitution of the interfacial Co60Fe40 layer for Co layer results in an enhancement of the interfacial exchange coupling eint and absolute dispersion of interfacial exchange coupling, σeint, and consequently increases the exchange bias field and reversal asymmetry.