Simultaneous mapping of EMCD signals and crystal orientations in a transmission electron microscope

Hasan Ali,Jan Rusz,Tobias Warnatz,Björgvin Hjörvarsson,Klaus Leifer

doi:10.1038/s41598-021-81071-4

Hasan Ali, Jan Rusz + Show 3 more

Open Access

https://doi.org/10.1038/s41598-021-81071-4

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Abstract

When magnetic properties are analysed in a transmission electron microscope using the technique of electron magnetic circular dichroism (EMCD), one of the critical parameters is the sample orientation. Since small orientation changes can have a strong impact on the measurement of the EMCD signal and such measurements need two separate measurements of conjugate EELS spectra, it is experimentally non-trivial to measure the EMCD signal as a function of sample orientation. Here, we have developed a methodology to simultaneously map the quantitative EMCD signals and the local orientation of the crystal. We analyse, both experimentally and by simulations, how the measured magnetic signals evolve with a change in the crystal tilt. Based on this analysis, we establish an accurate relationship between the crystal orientations and the EMCD signals. Our results demonstrate that a small variation in crystal tilt can significantly alter the strength of the EMCD signal. From an optimisation of the crystal orientation, we obtain quantitative EMCD measurements.

Highlights

Electron magnetic circular dichroism (EMCD)[1], a transmission electron microscope (TEM) based technique, has emerged as an important technique to determine the magnetic moments of the materials with much higher spatial resolution as compared to its X-ray counterpart XMCD2
/I0 at each beam position are representative of the specimen’s orientation we have performed simulations of diffraction patterns for both elastic and inelastic electron scattering of a parallel beam on an iron sample tilted into a systematic row orientation, while varying the Laue circle center
The L 3 and L2 difference signals, on the other hand, weaken or even change their sign in the misoriented regions. It seems that a change in crystal orientation away from the 2-beam condition (2BC) significantly influences the measured electron magnetic circular dichroism (EMCD)

Summary

Introduction

Electron magnetic circular dichroism (EMCD)[1], a transmission electron microscope (TEM) based technique, has emerged as an important technique to determine the magnetic moments of the materials with much higher spatial resolution as compared to its X-ray counterpart XMCD2. One of the apparently simple findings in the experimental evolution of the EMCD technique since its discovery is that the sample orientation and the electron beam position must be very well defined in order to obtain a quantitative EMCD signal. With this in mind, it is suprising that hitherto, the orientation dependence of the EMCD signal has not been analysed systematically in the experimental situation. Having acquired the STEM image of the atomic lattice of the magnetic material, the place of the EMCD analysis can be accurately determined It is non-trivial to obtain all information needed for highly accurate EMCD, i.e. orientation and both EELS spectra simultaneously. One of the major difficulties in such work consists in the serial acquisition of the two EELS spectra needed for the EMCD and the diffraction patterns at each beam position which make it hard to ensure the spatial registration among these measurements

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Conclusion