A study of perpendicular-anisotropy magnetic tunnel junction switched by spin-Hall-assisted spin-transfer torque

Current-induced spin-transfer torque (STT) is a mainstream method of switching the magnetization of free layer of magnetic tunnel junctions (MTJs) [1-2]. However, currently STT-MTJ is suffering from speed and energy bottlenecks caused by two tradeoffs: firstly, since the critical write current (I_c0) is proportional to the thermal stability barrier (Δ), it is difficult to reduce I_c0 without decreasing Δ. Secondly, the write current is limited to a relative small value to avoid the barrier breakdown, resulting in a low write speed. To overcome these bottlenecks, recent experiments [3-7] provide alternative write schemes in which spin Hall effect (SHE) and Rashba effect are used for switching the three-terminal MTJs (see Fig. 1). However, the applications of these schemes are hindered by some disadvantages: For switching a perpendicular-anisotropy MTJ (p-MTJ), both a charge current and an additional magnetic field are required (see Fig. 1(a)), which adds complexity to architecture. If an in-plane-anisotropy MTJ (i-MTJ) is used instead of p-MTJ, deterministic switching can be achieved by a charge current without the need of magnetic field (see Fig. 1(b)), but i-MTJ is inferior to p-MTJ in the scalability.