  Magnetic materials with strong perpendicular magnetic anisotropy are of great
interest for the development of nonvolatile magnetic memory and computing
technologies due to their high stabilities at the nanoscale. However,
electrical switching of such perpendicular magnetization in an
energy-efficient, deterministic, scalable manner has remained a big challenge.
This problem has recently attracted enormous efforts in the field of
spintronics. Here, I review recent advances and challenges in the understanding
of the electrical generation of spin currents, the switching mechanisms and the
switching strategies of perpendicular magnetization, the switching current
density by spin-orbit torque of transverse spins, the choice of perpendicular
magnetic materials, and summarize the progress in prototype perpendicular SOT
memory and logic devices toward the goal of energy-efficient, dense, fast
perpendicular spin-orbit torque applications.
