Magnetic domain control and voltage response of exchange biased magnetoelectric composites

Self-biased magnetoelectric composites, which are realized with the exchange bias effect, hold an increased total anisotropy field compared to systems without exchange bias. Thus, small exchange bias fields are favorable because of a minor reduction of magnetic permeability and magneto-electric voltage coefficient. However, weakly biased magnetoelectric composites lose their self-biasing properties and possibly show an increase of discontinuities in magnetization reversal due to the formation of magnetic domains. By a thickness variation of the ferromagnetic layer, a maximum voltage coefficient αME ≈ 430 V/cm Oe was found for a magnetostrictive multilayer of 3 × (5 nm Ta/3 nm Cu/8 nm Mn-Ir/333 nm Fe-Co-Si-B). Yet, a stable single domain state indicating a well defined magnetization reversal by coherent magnetization rotation was achieved for layer thicknesses up to 100 nm Fe-Co-Si-B with αME ≈ 340 V/cm Oe. This slight reduction is overcompensated by the improved control of the magnetic domain pattern which is highly beneficial for magnetic field sensing applications and of special importance, when frequency conversion techniques are applied.