Spin-orbit-torque magnetic random access memory (SOT-MRAM) is a promising technology for the next generation of data storage devices. The main bottleneck of this technology is the high reversal current density threshold. This outstanding problem is now solved by a new strategy in which the magnitude of the driven current density is fixed while the current direction varies with time. The theoretical limit of minimal reversal current density is only a fraction (the Gilbert damping coefficient) of the threshold current density of the conventional strategy. The Euler-Lagrange equation for the fastest magnetization reversal path and the optimal current pulse is derived for an arbitrary magnetic cell and arbitrary spin-orbit torque. The theoretical limit of minimal reversal current density and current density for a GHz switching rate of the new reversal strategy for CoFeB/Ta SOT-MRAMs are, respectively, of the order of ${10}^5$ ${\mathrm{A}/\mathrm{cm}}^2$ and ${10}^6$ ${\mathrm{A}/\mathrm{cm}}^2$ far below ${10}^7$ ${\mathrm{A}/\mathrm{cm}}^2$ and ${10}^8$ ${\mathrm{A}/\mathrm{cm}}^2$ in the conventional strategy. Furthermore, no external magnetic field is needed for a deterministic reversal in the new strategy.

• Received 26 December 2017
• Revised 7 February 2018

DOI:https://doi.org/10.1103/PhysRevB.97.144416