Change in interface magnetism of an exchange-coupled system due to the presence of nonmagnetic spacers

We report on the effect of nonmagnetic spacer layers on the interface magnetism and the exchange bias in the archetypical [Co/CoO] sub(16) system. The separation of the magnetic bilayers by Au layers with various thicknesses d sub(Au) > or = 25 nm leads to a threefold increase of the exchange bias field (H sub(eb)). Reflectometry with polarized neutrons does not reveal any appreciable change in the domain population. This result is in agreement with the observation that the granular microstructure within the [Co/CoO] bilayers is independent of d sub(Au). The significant reduction of the magnetic moments in the Co layers can be attributed to interfacial disorder at the Co-Au interfaces. Element-specific x-ray absorption spectroscopy attributes part of the enhancement of H sub(eb) to the formation of Co sub(3) O sub(4) in the [Co/CoO] bilayers within the multilayers. A considerable proportion of the increase of H sub(eb) can be attributed to the loss of magnetization at each of the Co-Au interfaces with increasing d sub(Au). We propose that the interfacial magnetism of ferro- and antiferromagnetic layers can be significantly altered by means of metallic spacer layers thus affecting the exchange bias significantly. This study shows that the magnetism in magnetic multilayers can be engineered by nonmagnetic spacer layers without involving the microstructure of the individual layers.