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In our numerical study, we identify the best conditions for efficient domain wall motion by spinorbit torques originating from the Spin Hall effect or Rashba effect. We demonstrate that the effect depends critically on the domain wall configuration, the current injection scheme and the symmetry of the spin-orbit torque. The best identified configuration corresponds to a Néel wall driven by spin Hall Effect in a narrow strip with perpendicular magnetic anisotropy. In this case, the domain wall velocity can be a factor of 10 larger than that for the conventional current-inplane spin-transfer torque.PACS : 75.70.Ak-75.60.Ch-75.78.FgThe fundamental concepts of spintronics are based on the generation, manipulation and detection of spin polarized currents. It has led in the last two decades to the development of a new generation of magnetic sensors, and notably read heads of hard disks and of non volatile magnetic memories (MRAM) that are expected to supplant semiconductor based memory devices. In classical spintronics, one generally creates a spin current by passing a charge current through a thin ferromagnetic layer, whose magnetization direction can be controlled by an external applied field or more efficiently by spin transfer torques. Recently an alternative way has emerged to control the magnetization configuration of a ferromagnetic layer that is based on current-induced spin-orbit (SO) torques, namely the Spin Hall Effects [1] and the Rashba effect [2]. Such SO torques are expected for magnetic stripes adjacent to a nonmagnetic conductive layer with strong spin-orbit interactions (SO layer) [3]. The exploitation of these SO effects 1

A review of the developments in MRAM technology over the past 20 years is presented. The various MRAM generations are described with a particular focus on Spin-Transfer-Torque MRAM (STT-MRAM) which is currently receiving the greatest attention. The working principles of these various MRAM generations, the status of their developments, and demonstrations of working circuits, including already commercialized MRAM products, are discussed.

We describe a new approach to understanding and calculating magnetization switching rates and noise in the recently observed phenomenon of "spin-torque switching". In this phenomenon, which has possible applications to information storage, a large current passing from a pinned ferromagnetic (FM) layer to a free FM layer switches the free layer. Our main result is that the spin-torque effect increases the Arrhenius factor $\exp(-E/kT)$ in the switching rate, not by lowering the barrier $E$, but by raising the effective spin temperature $T$. To calculate this effect quantitatively, we extend Kramers' 1940 treatment of reaction rates, deriving and solving a Fokker-Planck equation for the energy distribution including a current-induced spin torque of the Slonczewski type. This method can be used to calculate slow switching rates without long-time simulations; in this Letter we calculate rates for telegraph noise that are in good qualitative agreement with recent experiments. The method also allows the calculation of current-induced magnetic noise in CPP (current perpendicular to plane) spin valve read heads.Comment: 11 pages, 8 figures, 1 appendix Original version in Nature format, replaced by Phys. Rev. Letters format. No substantive change

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Spin-transfer torque magnetic random access memory (STT-MRAM) is a novel, magnetic memory technology that leverages the base platform established by an existing 100+nm node memory product called MRAM to enable a scalable nonvolatile memory solution for advanced process nodes. STT-MRAM features fast read and write times, small cell sizes of 6F 2 and potentially even smaller, and compatibility with existing DRAM and SRAM architecture with relatively small associated cost added. STT-MRAM is essentially a magnetic multilayer resistive element cell that is fabricated as an additional metal layer on top of conventional CMOS access transistors. In this review we give an overview of the existing STT-MRAM technologies currently in research and development across the world, as well as some specific discussion of results obtained at Grandis and with our foundry partners. We will show that in-plane STT-MRAM technology, particularly the DMTJ design, is a mature technology that meets all conventional requirements for an STT-MRAM cell to be a nonvolatile solution matching DRAM and/or SRAM drive circuitry. Exciting recent developments in perpendicular STT-MRAM also indicate that this type of STT-MRAM technology may reach maturity faster than expected, allowing even smaller cell size and product introduction at smaller nodes.

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We present spin transfer switching results for MgO based magnetic tunneling junctions (MTJs) with large tunneling magnetoresistance (TMR) ratio of up to 150 % and low intrinsic switching current density of 2-3 x 10 6 A/cm 2 . The switching data are compared to those obtained on similar MTJ nanostructures with AlO x barrier. It is observed that the switching current density for MgO based MTJs is 3-4 times smaller than that for AlO x based MTJs, and that can be attributed to higher tunneling spin polarization (TSP) in MgO based MTJs. In addition, we report a qualitative study of TSP for a set of samples, ranging from 0.22 for AlO x to 0.46 for MgO based MTJs, and that shows the TSP (at finite bias) responsible for the current-driven magnetization switching is suppressed as compared to zero-bias tunneling spin polarization determined from TMR.