Electron energy-loss magnetic chiral dichroism of magnetic iron film affected by an underlayer in a double-layer structure

Abstract

The electron energy-loss magnetic chiral dichroism (EMCD) technique has been generally applied to single-phase magnetic crystals while rarely used for composite structures. It is mainly due to the lack of in-depth understanding of EMCD in the latter case where an additional phase may present under or above the investigated magnetic phase in the electron beam path. Here, we report EMCD signals acquired on a 15-nm-thick magnetic iron film with different thicknesses of the MgO substrate underlayer. By comparison, for areas with total thicknesses of t=0.59λ and t=1.02λ expressed with the mean free inelastic path of electron λ, the relative dichroic signals at the Fe-L3 edge are 3.8%±1.0% and 3.5%±1.6%, respectively, demonstrating no significant difference within the error range. However, the dichroic signal intensity at the Fe-L2 edge peak is 77.6% larger in the thinner area of t=0.59λ. Accordingly, the extracted mL/ms ratio of Fe 3d moments is 63% smaller in the thinner area even after the plural scattering is removed. Then, we confirm that the presence of an additional nonmagnetic phase under a magnetic iron crystal can noticeably affect the quantified value of the mL/ms ratio of iron moment determined from the EMCD measurements. Furthermore, the larger thickness of the underlayer may result in relatively higher valuation of the mL/ms ratio of the upper layer. A correction method, considering the different influence of the underlayer on the Fe-L3 and L2 edges, is in demand for developing potential applications of the EMCD technique to such composite nanomaterial systems.