Ferromagnetic Resonance Spectroscopy, Micromagnetic Simulations and Scanning Transmission X-ray Microscopy as a toolbox for the characterization of magnetic nanoparticle ensembles*

Magnetic nanoparticles are studied for applications from medical research towards high performance computing using magnonic excitations. [1-3]. The understanding of their dynamic magnetic properties is a crucial task to bring such particle ensembles towards the application state. A characterization toolbox for these demands is the combination of Ferromagnetic Resonance (FMR) spectroscopy, micromagnetic simulations and element-specific (Time-Resolved) Scanning Transmission X-ray Microscopy (TR-STXM) [4][5], using X-ray Circular Magnetic Dichroism (XMCD) as contrast mechanism [6]. Here we present the use of this toolbox for the dynamic magnetic characterization of Fe₃O₄ nanoparticles ensembles naturally grown by biomineralization within magnetotactic bacteria of the species Magnetospirillum Magnetotacticum (average particle diameter 40 to 50 nm). In-plane angular dependent X-band FMR spectroscopy shows a multitude of angular dependent resonances exhibiting magnonic band gaps and crossings, well resembled by micromagnetic simulations. With TR-STXM we demonstrate the phase resolved sampling of magnetization dynamics of a nanoparticle ensemble of the same species showing a resonant response uniform in phase and non-uniform in amplitude with < 50 nm spatial resolution supplemented by micromagnetic simulations in good agreement [4]. 

References

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[2] A. Hoffmann and S.D. Bader. Physical Review Applied, 2015. 4(4): p. 047001-1-047001-18.

[3] B. Zingsem, T. Feggeler, et al. Nature Communications, 2019. 10: p. 4345.

[4] T. Feggeler, R. Meckenstock, et al. Physical Review Research, 2021. 3(3).

[5] S. Bonetti, R. Kukreja, et al. Review of Scientific Instruments, 2015. 86(9): p. 093703-1-093703-9.

[6] J. Stöhr and H.C. Siegmann, Magnetism From Fundamentals to Nanoscale Dynamics. Springer, ed. M. Cardona, et al. 2006, Berlin, Heidelberg: Springer.