  Reducing energy dissipation while increasing speed in computation and memory
is a long-standing challenge for spintronics research. In the last 20 years,
femtosecond lasers have emerged as a tool to control the magnetization in
specific magnetic materials at the picosecond timescale. However, the use of
ultrafast optics in integrated circuits and memories would require a major
paradigm shift. An ultrafast electrical control of the magnetization is far
preferable for integrated systems. Here we demonstrate reliable and
deterministic control of the out-of-plane magnetization of a 1 nm-thick Co
layer with single 6 ps-wide electrical pulses that induce spin-orbit torques on
the magnetization. We can monitor the ultrafast magnetization dynamics due to
the spin-orbit torques on sub-picosecond timescales, thus far accessible only
by numerical simulations. Due to the short duration of our pulses, we enter a
counter-intuitive regime of switching where heat dissipation assists the
reversal. Moreover, we estimate a low energy cost to switch the magnetization,
projecting to below 1fJ for a (20 nm)^3 cell. These experiments prove that
spintronic phenomena can be exploited on picosecond time-scales for full
magnetic control and should launch a new regime of ultrafast spin torque
studies and applications.
