  Many key electronic technologies (e.g., large-scale computing, machine
learning, and superconducting electronics) require new memories that are fast,
reliable, energy-efficient, and of low-impedance at the same time, which has
remained a challenge. Non-volatile magnetoresistive random access memories
(MRAMs) driven by spin-orbit torques (SOTs) have promise to be faster and more
energy-efficient than conventional semiconductor and spin-transfer-torque
magnetic memories. This work reports that the spin Hall effect of
low-resistivity Au0.25Pt0.75 thin films enables ultrafast antidamping-torque
switching of SOT-MRAM devices for current pulse widths as short as 200 ps. If
combined with industrial-quality lithography and already-demonstrated
interfacial engineering, our results show that an optimized MRAM cell based on
Au0.25Pt0.75 can have energy-efficient, ultrafast, and reliable switching, e.g.
a write energy of < 1 fJ (< 50 fJ) for write error rate of 50% (<1e-5) for 1 ns
pulses. The antidamping torque switching of the Au0.25Pt0.75 devices is 10
times faster than expected from a rigid macrospin model, most likely because of
the fast micromagnetics due to the enhanced non-uniformity within the free
layer. These results demonstrate the feasibility of Au0.25Pt0.75-based
SOT-MRAMs as a candidate for ultrafast, reliable, energy-efficient,
low-impedance, and unlimited-endurance memory.
