Sub-ns magnetic domain wall motion dynamics

Since the first discovery that magnetic domain walls can be displaced by electrical currents through spin-transfer and spin-orbit torques, the current-induced domain wall motion (CIDWM) effect has been object of attention in the scientific community. This is due to the interesting applications of the CIDWM effect, such as e.g. the possibility of fabricating magnetic memories that combine long-term data retention with the absence of mechanically moving parts. The experimental investigation of the sub-ns dynamical processes of the domain wall motion dynamics is of paramount importance for the understanding of the physical processes governing the CIDWM process. However, due to numerous experimental challenges, the domain wall motion dynamics at the sub-ns timescale have long eluded a direct experimental investigation.

In this work, we were able to overcome these experimental challenges and perform pump-probe dynamical investigations using time-resolved scanning transmission x-ray microscopy of the current- and magnetic field-induced domain wall motion in a perpendicularly magnetized (PMA) material exhibiting anti-symmetric exchange interaction combining high spatial and temporal resolutions. This work was carried out as a collaborative effort between the magnetism research team of the PolLux endstation and the group of Prof. Christopher Marrows at the University of Leeds.

Thanks to the sub-ns time step employed for the imaging of the domain wall dynamics, we were able to observe that the motion of the magnetic domain walls occurs synchronously with the onset of the electrical current/magnetic field excitation (within an error of 200 ps), providing strong indications for the absence of inertia in the domain walls of the PMA material. Furthermore, we observed that, for short current and magnetic field pulses, the magnetic domain walls do not exhibit a tilting during its motion, providing a potential mechanism for the fast, tilt-free, current-induced motion of magnetic domain walls. These findings will provide a substantial step forward towards the understanding of the physical processes behind the current- and magnetic field-induced motion of magnetic domain walls.