Suppression of magnetization ripple by exchange bias

Abstract

We present a magnetic domain imaging study of polycrystalline exchange biased ferromagnet/ antiferromagnet Co/FeMn bilayers using x-ray photoelectron emission microscopy. At low FeMn thicknesses, where the system exhibits no exchange bias, a magnetic fine structure due to fluctuations of the local anisotropy axis is observed in the ferromagnetic Co layer. We find that upon increasing the FeMn layer thickness, this dispersion of the magnetization of the ferromagnetic layer is increasingly suppressed. This can be interpreted as influence of the exchange bias field on the spin structure of the ferromagnetic layer, mediated by the interface coupling, if the “exchange length” analogous to a domain-wall width of the antiferromagnetic layer is larger than that of the ferromagnetic layer. The same behavior is observed for both the induced Fe and Mn ferromagnetic moments in the antiferromagnetic layer. We illustrate that the final spin structure at the Co/FeMn interface is not only governed by the magnetic spin structure of the Co layer alone which is the general perception but is also an exchange average of both the Co and FeMn layers.