STEM-EELS analysis of interface magnetic moments in Fe(100)/Co(bcc) superlattices

Abstract

Information on the magnetic moment can be obtained experimentally by Electron Energy Loss Spectroscopy (EELS) at the L_2,3 edge of iron, since the moment depends upon the Fe-3d band occupancy [1,2]. Experimental works have for instance shown that the Fe-I(L₃)/I(L₂) ratio is directly correlated to the Fe magnetic moment for an important number of compounds and alloys containing iron [2,3,4,5,6]. In this contribution, we focus on the magnetic moment modification induced by the interfaces of a thin iron layer. Local and averaged values of the I(L₃)/I(L₂) ratio have been measured in cross sectional sample, and for several Fe(n atomic layers)/Co(3 atomic layers) bcc superlattices, with n=3,5,10,20, grown by Molecular Beam Epitaxy (MBE) on a single crystal Fe(100) buffer, see Fig. 1. The samples differ one from the others by the iron layer thickness. The Fe-I(L₃)/I(L₂) ratio measured in the superlattices is higher than the Fe buffer value and increases when the number of atomic planes in the thin iron layer of the Fe/Co superlattice decreases. This can be clearly seen in Fig. 2. These variations of the L_2,3 ratio can be interpreted in term of an interface-induced enhancement of the Fe spin magnetic moment: This has been confirmed by ab-inito calculations of the magnetic moment for the superlattices corresponding to our samples. The relative modification of the L_2,3 ratio and of the calculated spin magnetic moment can be compared. They are of the same order of magnitude and increase when the proportion of iron atoms which are located at the interface increases.