Visualization of spin-wave propagation dynamics using laser-free GHz stroboscopic transmission electron microscopy

Spin waves, also known as magnons, have the potential to play a vital role as information carriers in spintronics. Their lower energy damping, short wavelength and spin intrinsic nature, promise high-speed data processing in conventional and quantum information transmission. Although several experimental techniques have already been applied to study magnons, imaging spin wave dynamics with sufficient spatial resolution remains a challenge.

With the development of the laser-free ultrafast electron microscope (UEM) at Brookhaven National Laboratory, direct visualization of materials’ structural dynamics with nanometer-picosecond spatiotemporal resolution can be achieved. Instead of using laser pulses as the excitation pump, transverse radio frequency (RF) electrical signals are sent to the sample devices via an impedance matched RF sample holder. The dynamics can then be probed by the temporally synchronized electron pulse-trains generated by a RF cavity installed in the UEM.

In this work, we study the spin-wave propagation dynamics in patterned permalloy (Py, Ni₈₀Fe₂₀) thin films using the laser-free UEM in Lorentz mode. Oscillating magnetic fields generated by the microwave currents are applied as local excitation to the Py pattern via a coplanar waveguide (CPW). The dynamics of spin-wave excitation from various magnetic domain configurations will be reported and discussed. Micromagnetic simulations will also be presented to compare with the experimental results.