  We investigated the magnetization reversal of a perpendicularly magnetized
nanodevice using a chirped current pulse (CCP) via spin-orbit torques (SOT).
Our findings demonstrate that both the field-like (FL) and damping-like (DL)
components of SOT in CCP can efficiently induce ultrafast magnetization
reversal without any symmetry-breaking means. For a wide frequency range of the
CCP, the minimal current density obtained is significantly smaller compared to
the current density of conventional SOT-reversal. This ultrafast reversal is
due to the CCP triggering enhanced energy absorption (emission) of the
magnetization from (to) the FL- and DL-components of SOT before (after)
crossing over the energy barrier. We also verified the robustness of the
CCP-driven magnetization reversal at room temperature. Moreover, this strategy
can be extended to switch the magnetic states of perpendicular synthetic
antiferromagnetic (SAF) and ferrimagnetic (SFi) nanodevices. Therefore, these
studies enrich the basic understanding of field-free SOT-reversal and provide a
novel way to realize ultrafast SOT-MRAM devices with various free layer
designs: ferromagnetic, SAF, and SFi.
