Long-range interlayer-coupled magnetization reversal mediated by the antiferromagnetic layer in Py/FeMn/CoFe trilayers

With a combination of vector magneto-optical Kerr effect magnetometry and polarized neutron reflectometry, the detailed magnetization reversal mechanism of the exchange-biased Py(30-nm)/FeMn[t_AFM = (0-30)-nm]/CoFe(30-nm) trilayers was studied. We found that Py/FeMn(15-nm) and FeMn(15-nm)/CoFe bilayers show completely different magnetization reversal modes, whereas they become very similar to each other in the corresponding Py/FeMn/CoFe trilayers. This is convincing evidence that the 15-nm FeMn layer mediates the magnetization reversal behaviors of both Py and CoFe layers through interlayer exchange bias coupling. Furthermore, magnetization reversal of Py and CoFe layers are decoupled for t_AFM=30 nm, indicating that the exchange length the magnetization reversal between two adjacent ferromagnetic layers is correlated over is less than 30 nm. This is in reasonable agreement with the theoretically predicted domain-wall width such as 28 nm for the polycrystalline FeMn/Co bilayer and 50 nm for the perfect Fe₅₀Mn₅₀ crystal.