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Measurement of local magnetic properties of devices with transmission electron microscopy

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Energy-loss magnetic chiral dichroism (EMCD), which was experimentally realized by P. Schattschneider et al. for the first time in 2006, is a technique based on electron energy-loss spectroscopy (EELS). It aims at measuring the element-specific local magnetic moment of solids at a nanometer scale. Compared to its analogue X-ray magnetic circular dichroism (XMCD), EMCD has its potential advantage in spatial resolution. In recent years, EMCD studies of 3d transition metal atoms or ions in cubic crystals have been extensively performed, and its experimental setups, data processing methods as well as the application of sum rules have been constantly improved. With promising prospects, EMCD is still on its way to be a routine magnetic characterization technique. It is of importance to apply this technique to different groups of elements and crystal systems, for investigating its sensitivity in different cases and further extending its applications.

In this talk, I will present the EMCD studies of epitaxial MnAs thin films grown on a GaAs(001) substrate and DyFe2/YFe2 superlattices. The 3d orbital-to-spin moment ratio of Mn in hexagonal ferromagnetic MnAs along easy, hard and intermediate magnetic axes was estimated by EMCD . Moreover, a breaking of the ferromagnetic order in MnAs thin film, together with the crystallographic transition from hexagonal α-MnAs to quasi-hexagonal β-MnAs, was locally observed in-situ by modifying the temperature of the crystal inside the electron microscope. In addition, I will show a simultaneous probe of 3d and 4f moments by investigating Fe-L2,3 and Dy-M4,5 edges in DyFe2/YFe2 superlattices. EMCD signals of both Fe and Dy were observed. Sum rules exclusively for M4,5 edges were derived. The antiparallel alignment of net Dy and Fe moments was confirmed, taking into account the dynamic diffraction effects. The work illustrates for the first time the feasibility of EMCD technique for quantitative study of magnetocrystalline anisotropy and magnetic transition, and also proves its potential as a tool to investigate 4f moment as well as moment coupling in magnetic materials.

This talk is part of the Electron Microscopy Group Seminars series.

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