the paper presents our simulated results showing the substantial improvement of both switching speed and energy consumption in a perpendicular magnetic tunnel junction (p-MTJ), a core unit of Spin-Transfer-Torque Magnetic Random Access Memory (STT-MRAM), by the help of additional Spin-Orbit-Torque (SOT) write pulse current (WP Sot ). An STT-SOT hybrid torque module for OOMMF simulation is implemented to investigate the switching behavior of a 20 nm cell in the p-MTJ. We found that the assistance of WP Sot to STT write pulse current (WP Stt ) have a huge influence on the switching behavior of the free layer in the p-MTJ. For example, we could dramatically reduce the switching time (t SW ) by 80% and thereby reduce the write energy over 70% as compared to those in the absence of the WP Sot . Even a very tiny amplitude of WP Sot (J Sot of the order of 10 2 A/m 2 ) substantially assists to reduce the critical current density for switching of the free layer and thereby decreases the energy consumption as well. It is worth to be pointed out that the energy can be saved further by tuning the WP Sot parameters, i.e., amplitude and duration along at the threshold WP Stt . Our findings show that the proposed STT-SOT hybrid switching scheme has a great impact on the MRAM technology seeking the high speed and low energy consumption.Magnetic Random Access Memory (MRAM) has known to be an outstanding candidate among next-generation memories due to its various advantages, such as non-volatility, high-speed operation, high density and scalability, over other competing memories 1-4 . In particular, spin-transfer torque MRAM (STT-MRAM) composed of perpendicular magnetic tunnel junctions (p-MTJs) has received a significant attention because it offers reduced write current and strong thermal stability 5 . In an MTJ, there are two ferromagnetic (FM) layers separated by an insulating tunneling barrier. One FM layer has a fixed magnetization and another has a variable magnetization (called as a free layer) which can be made to align either parallel (P) or anti-parallel (AP) with respect to the fixed layer. Magnetization of the free layer is used to store the data and can be switched by spin-polarized electrons (equivalently spin current) without a magnetic field. When the spin-polarized current flows through the free layer, the layer absorbs spin angular momentum from the electrons and as a result, its magnetization flips, which is the reason why we call it spin (momentum) transfer torque. STT-MRAM faces various challenges along with its merits such as, the reliability of a tunnel barrier, long write latency and small energy efficiency due to still high write current. Out of these, the most important issue which needs to be counter first is high energy consumption due to high write current and long write latency. The current density for switching of STT-MRAM is relatively large and hence large transistors are inevitable to drive it, which thus significantly limits their future use for memory applications 6,7 . The sustainability of hig...

Owing to their remarkable spin−charge conversion (SCC) efficiency, topological insulators (TIs) are the most attractive candidates for spin−orbit torque generators. The simple method of enhancing SCC efficiency is to reduce the thickness of TI films to minimize the trivial bulk contribution. However, when the thickness reaches the ultrathin regime, the SCC efficiency decreases owing to intersurface hybridization. To overcome these contrary effects, we induced dehybridization of the ultrathin TI film by breaking the inversion symmetry between surfaces. For the TI film grown on an oxygen-deficient transition-metal oxide, the unbonded transition-metal d-orbitals affected only the bottom surface, resulting in asymmetric surface band structures. Spintronic terahertz emission spectroscopy, an emerging tool for investigating the SCC characteristics, revealed that the resulting SCC efficiency in symmetry-broken ultrathin Bi 2 Se 3 was enhanced by up to ∼2.4 times.

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