Magnetization reversal in trained exchange biased multilayers

FM magnetization may be collinear (responsible for nonuniform reversal) or noncollinear (responsible for uniform reversal) to the direction of the applied field in ferromagnetic-antiferromagnetic (FM-AF) exchange-biased systems depending upon the number of field cycles it has undergone. Usually noncollinearity sets in right after the first field cycle, i.e.when the system is in the trained state. Here we show that in case of polycrystalline multilayers (MLs) of continuous AF-FM interfaces (ML-C), e.g.in [Co/CoO] ₂₀, this collinearity of the FM magnetization remains not only in the untrained state but even in the trained state as each FM layer in the ML remagnetizes symmetrically for both field branches via the nonuniform mode only. Thus the state of magnetization can remain virtually unaffected by repeated field cycling, and this can be exploited in building stable state spin-valve systems.