Unveiling the impact of temperature on magnon diffuse scattering detection in scanning transmission electron microscopy

Magnon diffuse scattering (MDS) signals could be studied with high spatial resolution in scanning transmission electron microscopy (STEM), thanks to recent technological progress in electron energy loss spectroscopy. However, detecting MDS signals in STEM is challenging due to their overlap with the stronger thermal diffuse scattering (TDS) signals. In bcc Fe at 300~K, MDS signals greater than or comparable to TDS signals occur under the central Bragg disk, into a currently inaccesible energy-loss region. Therefore, to detect MDS in STEM, it is necessary to identify conditions in which TDS and MDS signals can be distinguished from one another. Temperature may be a key factor due to the distinct thermal signatures of magnon and phonon signals. In this work, we present a study on the effects of temperature on MDS and TDS in bcc Fe -- considering a detector outside the central Bragg disk -- using the frozen phonon and frozen magnon multislice methods. Our study reveals that neglecting the effects of atomic vibrations causes the MDS signal to grow approximately linearly up to the Curie temperature of Fe, after which it exhibits less variation. The MDS signal displays an alternating behavior due to dynamical diffraction, instead of increasing monotonically as a function of thickness. The inclusion of the Debye-Waller factor (DWF) causes the linear growth of the MDS signal to change to an oscillatory behavior that exhibits a predominant peak for each thickness, which increases and shifts to higher temperatures as the thickness increases. In contrast, the TDS signal grows more linearly than the MDS signal (with DWF) but still exhibits dynamical diffraction effects. An analysis of the signal-to-noise ratio (SNR) shows that the MDS signal can be a statistically significant contribution to the total scattering intensity under realistic measurement conditions and reasonable acquisition times.