Nearly a decade since first demonstration, vibrational electron-energy-loss spectroscopy has pushed the capabilities of analytical in a scanning transmission electron microscope (STEM) [1]. Phonon eigen modes can now be detected at atomic resolution [2], along with their dispersion in momentum space [3], and related to local atomic structure and chemistry. Magnons are quasiparticles representing the collective excitation of spins in magnetic materials. They, along with hybrid magnon-phonon quasiparticles (magnon polarons), are the basis for the operation of new spin wave transfer logic devices. They occupy the same energy loss windows as phonon modes, suggesting that STEM-EELS may offer the ability to detect them at the nanoscale. Here, we show that bulk THz magnons can be excited and detected at the nanoscale using high-energy-resolution STEM EELS [4] with the help of hybrid-pixel electron detectors. Momentum-resolved (ω-q) vibrational EELS measurements on antiferromagnetic material systems reveal the unambiguous dispersion behaviour of the magnon signal (Fig. 1) in NiO. The experimental findings are shown to be in excellent agreement with theoretical momentum-resolved magnon EELS dispersion curves (Fig. 1), calculated using theoretical methodologies to electron inelastic scattering of magnons and phonon-magnon coupling in an electron microscope [5]. Finally, we explore the limits of spatial resolution, by performing atomically resolved measurements and discuss of the contrast formation in atomically resolved magnon maps.
[1] O.L. Krivanek et al, Nature 514, 209, (2014).
[2] F.S. Hage et al, Science 367, 1124-1127, (2020).
[3] F.S. Hage et al, Science Advances 4, eaar7495, (2018).
[4] D.M. Kepaptsoglou et al, Nature 644, pages83–88 (2025)
[5] J.Á. Castellanos-Reyes et al, Phys. Rev. Let. 134, 036402 (2025).