“External forces” are indispensable for the occurrence of exchange bias?

Abstract

We demonstrate here a double-shifted exchange bias which spontaneously exists in the as-deposited [Pt/Co]n/IrMn multilayers without resorting to any “external forces,” such as deposition with field, field annealing, (zero) field cooling with specific procedures. The observed results indicate that the exchange bias might occur spontaneously when a ferromagnetic layer is in contact with an antiferromagnetic layer; herein it is tentatively attributed to interactions among perpendicular anisotropy of [Pt/Co]n multilayers, its intrinsic demagnetization field, and magnetic anisotropy of the IrMn layer. The thickness and the magnitude of magnetic anisotropy of the ferromagnetic multilayer are crucial for the adjustment of asymmetric double-shifted exchange bias which can also be tuned to exist in the in-plane or out-of-plane directions.