Size-dependent scaling of perpendicular exchange bias in magnetic nanostructures

Size-dependent scaling is studied in exchange biased nanostructures obtained by depositing [Pt∕Co]₃∕IrMn multilayers with perpendicular magnetization onto an array of monodisperse polystyrene nanospheres with a diameter ranging from 580.3em0exnm to 3200.3em0exnm. We find that the exchange bias field increases with the inverse of the sphere diameter when the IrMn layer is single domain. This scaling behavior, which is favorable for further miniaturization of magnetic devices, can be understood within the context of a random field model by a statistical distribution of Mn spins at the Co∕IrMn interface.