The double-shifted magnetic hysteresis loops and domain structure in perpendicular [Co/Ni]_N/IrMn exchange biased systems

The double-shifted magnetic hysteresis loops, which are accompanied by the formation of bi-domain state, are normally observed after zero field cooling a demagnetized sample or as-deposited ferromagnetic (FM)/antiferromagnetic (AFM) structures. In the pioneer works, this phenomenon was explained by the imprinting of ferromagnetic FM domain in AFM layer, however the interaction between the FM and AFM domain has never been discussed. In this work, we observed double-shifted magnetic hysteresis loops and bi-domain state in [Co 0.3/Ni 0.4i]_N/IrMn multilayers with perpendicualr magnetic anisotropy. By comparing the domain patterns in (Co 0.3/Ni 0.4)_N/IrMn multilayers, we may conclude that the bi-domain state in FM/AFM structure is related to both the FM and AFM domain, and the domain size is determined by the minimum of the total energy in the FM/AFM system through the interficial coupling. (paper)