Electron energy-loss magnetic chiral dichroism (EMCD), which is the electron wave analogue of X-ray magnetic circular dichroism (XMCD), offers the possibility to study magnetic properties at the nanoscale in a TEM. The relatively young method of EMCD  was already refined to such an extent that it is possible to probe magnetic moments of thin films of a variety of ferromagnets [2, 3, 4]. By now, these measurements already surpass the resolution of XMCD experiments. However, quantitative EMCD measurements are so far only reported on thin films rather than on nanoparticles, which are expected to reveal distinct magnetic properties due to their reduced dimensions and enhanced surface to volume ratio.
We report on EMCD measurements on a single FePt nanoparticle (cf. Figure 1) and compare our experimental findings with simulations. L10 ordered FePt is a particularly interesting material since it offers the highest magneto-crystalline anisotropy among the oxidation-resistant hard magnets . It is therefore a promising material for future high density magnetic data storage media. The L10 ordered FePt nanoparticles on a STO substrate were prepared by sputtering. Prior to the spectroscopic measurements, samples in plan view geometry were subjected to mechanical thinning and grazing incidence Ar+ ion milling in order to obtain 10 nm thick substrate-free nanoparticles.
The experiments were performed on a FEI Titan3 80-300 microscope equipped with an image CS corrector. The sample was oriented in three beam condition with the  easy axis of L10 FePt oriented (close to) parallel to the electron beam. Binned-gain acquisition of the EEL spectra was used to optimize the S/N ratio . Particular attention was paid to the analysis of the EEL spectra. A measurement route is presented that allows for the extraction of a dichroic signal from spectra that still suffer from non-optimal S/N ratio. Our experiments are supported by simulations of EEL spectra utilizing the WIEN2k program package  in combination with Bloch-wave (BW) methods. These simulations are used to (pre-)determine optimal experimental parameters, that provide for the highest EMCD signals [8, 9]. The experiments reveal a small but reproducible dichroic signal (cf. Figure 2) that agrees well with the results of the theoretical calculations. From these experimental spectra, a ratio of angular to spin magnetic moment ml/ms = 0.08 ± 0.08 is for the first time quantitatively derived for individual FePt nanoparticles , which agrees well with the XMCD result ml/ms = 0.09 for a large ensemble of L10 ordered FePt nanoparticles .
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P. Schattschneider acknowledges financial support by the Austrian Science Fund (FWF) under grant nr. I543-N20. S. Löffler acknowledges financial support by the Austrian Science Fund (FWF) under grant nr. J3732-N27.
To cite this abstract:Sebastian Schneider, Darius Pohl, Stefan Löffler, Deepa Kasinathan, Jan Rusz, Peter Schattschneider, Ludwig Schultz, Bernd Rellinghaus; Quantifying magnetism on the nanometer scale: EMCD on individual FePt nanoparticles. The 16th European Microscopy Congress, Lyon, France. https://emc-proceedings.com/abstract/quantifying-magnetism-on-the-nanometer-scale-emcd-on-individual-fept-nanoparticles/. Accessed: November 27, 2022
EMC Abstracts - https://emc-proceedings.com/abstract/quantifying-magnetism-on-the-nanometer-scale-emcd-on-individual-fept-nanoparticles/