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Resistive switching devices, important for emerging memory and neuromorphic applications, face significant challenges related to control of delicate filamentary states in the oxide material. As a device switches, its rapid conductivity change is involved in a positive feedback process that would lead to runaway destruction of the cell without current, voltage, or energy limitation. Typically, cells are directly patterned on MOS transistors to limit the current, but this approach is very restrictive as the necessary integration limits the materials available as well as the fabrication cycle time. In this article we propose an external circuit to cycle resistive memory cells, capturing the full transfer curves while driving the cells in such a way to suppress runaway transitions. Using this circuit, we demonstrate the acquisition of $10^5$ I-V loops per second without the use of on-wafer current limiting transistors. This setup brings voltage sweeping measurements to a relevant timescale for applications, and enables many new experimental possibilities for device evaluation in a statistical context.

In this work, we use a Cr-doped V2O3 based Mott oscillator circuit to build a reservoir computing system that has much smaller model size than an equivalent LSTM. In contrast to an LSTM, our reservoir computing system can be trained very efficiently and on-line, with very low latency. We demonstrate close to state-of-the-art performance with three benchmark tasks: speech recognition, handwritten digit recognition, and HDD channel decoding. We show that our Mott circuit-based reservoir computing system brings significant reduction in power consumption and inference speed compared to CPU, GPU, or FPGA based systems.

In cloud and edge computing models, it is important that compute devices at the edge be as power efficient as possible. Long short-term memory (LSTM) neural networks have been widely used for natural language processing, time series prediction and many other sequential data tasks. Thus, for these applications there is increasing need for low-power accelerators for LSTM model inference at the edge. In order to reduce power dissipation due to data transfers within inference devices, there has been significant interest in accelerating vector-matrix multiplication (VMM) operations using non-volatile memory (NVM) weight arrays. In NVM array-based hardware, reduced bit-widths also significantly increases the power efficiency. In this paper, we focus on the application of quantization-aware training algorithm to LSTM models, and the benefits these models bring in terms of resilience against both quantization error and analog device noise. We have shown that only 4-bit NVM weights and 4-bit ADC/DACs are needed to produce equivalent LSTM network performance as floating-point baseline. Reasonable levels of ADC quantization noise and weight noise can be naturally tolerated within our NVMbased quantized LSTM network. Benchmark analysis of our proposed LSTM accelerator for inference has shown at least 2.4x better computing efficiency and 40x higher area efficiency than traditional digital approaches (GPU, FPGA, and ASIC). Some other novel approaches based on NVM promise to deliver higher computing efficiency (up to 4.7x) but require larger arrays with potential higher error rates., Comment: Published in: 2019 IEEE International Conference on Rebooting Computing (ICRC)

The switching speed of a threshold switching Cr-doped V 2 O 3 device as function of voltage and resistive load is understood by means of a thermal device model. It is found that conditions that result in switching trajectories traveling further from equilibrium result in reduced switching time and energy, providing interesting guidelines for the optimization of the 1S1R memory cell. Secondly, the addition of capacitive loads is investigated. Voltage-controlled oscillatory behavior in the frequency range of 10–30 MHz has been obtained and also properly simulated by our device model. Such nanodevice oscillators are of high interest for new neuromorphic computing paradigms.

Recording experiments and decoding algorithms are presented for evaluating the bit error rate (BER) of state-of-the-art magnetic bit-patterned media (BPM). The recording experiments are performed with a static tester and conventional hard-disk drive heads. As the reader dimensions are larger than the bit dimensions in both the down-track and the cross-track directions, a 2-D bit-decoding algorithm is required. Two such algorithms are presented in detail together with the methodology implemented to accurately retrieve island positions during recording. Using these techniques, a 1.6 Td/in2 magnetic BPM is demonstrated to support 2-D BER below 1e-2 under shingled magnetic recording conditions.

In this work, thin film (down to 10 nm) $(\mathrm{V}_{1-\mathrm{x}}\text{Cr}_{\mathrm{x}})_{2}\mathrm{O}_{3}$ Mott-oxide based nano-devices (electrode width down to 120 nm) are fabricated for the first time. The devices show volatile threshold switching and NDR caused by thermal feedback. Fast ( $(\mathrm{V}_{1-\mathrm{x}}\text{Cr}_{\mathrm{x}})_{2}\mathrm{O}_{3}$ films, enabling predictions for further scaled device geometries.

Bit patterned media (BPM) provide an alternative to conventional granular thin film recording media, circumventing the challenges of managing grain size and its associated noise and thermal stability issues in granular media. A viable fabrication strategy involves creation of a master pattern by rotary-stage e-beam lithography and directed self-assembly of block copolymers, followed by pattern replication via UV-cure nanoimprint lithography and pattern transfer to a magnetic thin film by ion beam etching. These steps have been demonstrated for 150 Gdot/cm2 (1 Tdot/in2) hcp patterns, achieving a dot placement tolerance of 1.2 nm 1σ and a defect rate of ; 1. A master pattern generation generation strategy for BAR>; 1 with rectangular islands is shown using intersecting lines generated by directed self-assembly of lamellar block copolymers in combination with spacer-defined line doubling.

We present a method for growing bit patterned magnetic recording media using directed growth of sputtered granular perpendicular magnetic recording media. The grain nucleation is templated using an epitaxial seed layer, which contains Pt pillars separated by amorphous metal oxide. The scheme enables the creation of both templated data and servo regions suitable for high density hard disk drive operation. We illustrate the importance of using a process that is both topographically and chemically driven to achieve high quality media.

Ferromagnetic resonance (FMR) spectroscopy, x-ray magnetic circular dichroism (XMCD) spectroscopy and magnetic transmission soft x-ray microscopy (MTXM) experiments have been performed to gain insight into the magnetic anisotropy and domain structure of ultrathin Co | Ni multilayer films with a thin permalloy layer underneath. MTXM images with a spatial resolution better than 25 nm were obtained at the Co L3 edge down to an equivalent thickness of Co of only 1 nm, which establishes a new lower boundary on the sensitivity limit of MTXM. Domain sizes are shown to be strong functions of the anisotropy and thickness of the film.

An experimental study of domain wall motion in Ni80Fe20 ring structures induced by current pulses as well as conventional magnetic fields is presented. Using constrictions we demonstrate that current-induced domain wall motion can be used to displace walls into parts of the structure where no pulsed currents are flowing. Measurements at variable temperatures between 2 and 300 K show that the fields necessary for wall motion decrease with increasing temperature, which can be explained by thermal activation. For the current-induced case we find, depending on the geometry and temperature range, that the current densities necessary for displacement can increase or decrease with rising temperature. This indicates that, in addition to thermal excitations, an intrinsic temperature dependence of the efficiency of the spin torque effect is present and leads to an increase in the critical current density with increasing temperature.

Bit Patterned Media (BPM) for magnetic recording provide a route to densities $>1 Tb/in^2$ and circumvents many of the challenges associated with conventional granular media technology. Instead of recording a bit on an ensemble of random grains, BPM uses an array of lithographically defined isolated magnetic islands, each of which stores one bit. Fabrication of BPM is viewed as the greatest challenge for its commercialization. In this article we describe a BPM fabrication method which combines e-beam lithography, directed self-assembly of block copolymers, self-aligned double patterning, nanoimprint lithography, and ion milling to generate BPM based on CoCrPt alloys. This combination of fabrication technologies achieves feature sizes of $, 44 pages

Stimulated Brillouin backscattering (SBS) is studied in multimode glass fibers with core diameters between 25 and 200 μm . The SBS threshold energy, and damage threshold were measured. High SBS reflectivities over 80% are obtained with 30 ns laser pulses at 1.06 μm wavelength. The experimental results regarding the SBS reflectivity are compared with an analytical calculation for a plane wave model of the SBS process. The Brillouin gain coefficient of the fibers appeared to be about equal to the bulk gain coefficient.

Équipe 101 : Nanomagnétisme et électronique de spin; International audience; We present a systematic experimental study of the spin-torque-induced magnetic switching statistics at room temperature, using all-perpendicularly magnetized spin-valves as a model system. Three physical regimes are distinguished: a short-time ballistic limit below a few nanoseconds, where spin-torque dominates the reversal dynamics from a thermal distribution of initial conditions; a long time limit, where the magnetization reversal probability is determined by spin-torque-amplified thermal activation; and a cross-over regime, where the spin-torque and thermal agitation both contribute. For a basic quantitative understanding of the physical processes involved, an analytical macrospin model is presented which contains both spin-torque dynamics and finite temperature effects. The latter was treated rigorously using a Fokker-Plank formalism, and solved numerically for specific sets of parameters relevant to the experiments to determine the switching probability behavior in the short time and cross over regimes. This analysis shows that thermal fluctuations during magnetization reversal greatly affect the switching probability over all the time scales studied, even in the short time limit. (C) 2014 Elsevier B.V. All rights reserved

Switching field measurements of the free layer element of 75 nm diameter spin-valve nanopillars reveal a bimodal distribution of switching fields at low temperatures (below 100 K). This result is inconsistent with a model of thermal activation over a single perpendicular anisotropy barrier. The correlation between antiparallel to parallel and parallel to antiparallel switching fields increases to nearly 50% at low temperatures. This reflects random fluctuation of the shift of the free layer hysteresis loop between two different magnitudes, which may originate from changes in the dipole field from the polarizing layer. The magnitude of the loop shift changes by 25% and is correlated to transitions of the spin-valve into an antiparallel configuration., 3 pages, 4 figures. Submitted to JAP for 58th MMM Proceedings

Équipe 101 : Nanomagnétisme et électronique de spin; International audience; We present switching field distributions of spin-transfer-assisted magnetization reversal in perpendicularly magnetized Co/Ni multilayer spin-valve nanopillars at room temperature. Switching field measurements of the Co/Ni free layer of spin-valve nanopillars with a 50 nm x 300 nm ellipse cross section were conducted as a function of current. The validity of a model that assumes a spin-current-dependent effective barrier for thermally activated reversal is tested by measuring switching field distributions under applied direct currents. We show that the switching field distributions deviate significantly from the double exponential shape predicted by the effective barrier model, beginning at applied currents as low as half of the zero field critical current. Barrier heights extracted from switching field distributions for currents below this threshold are a monotonic function of the current. However, the thermally induced switching model breaks down for currents exceeding the critical threshold.

Equipe 101 : Nanomagnétisme et électronique de spin; International audience; We present temperature dependent switching measurements of the Co/Ni multilayered free element of 75-nm-diameter spin-valve nanopillars. Angular dependent hysteresis measurements as well as switching field measurements taken at low temperature are in agreement with a model of thermal activation over a perpendicular anisotropy barrier. However, the statistics of switching (i.e. the mean switching field and the variance of the switching field distribution) from 20 up to 400 K are in disagreement with a Neel-Brown model that assumes a temperature independent barrier height and anisotropy field. We introduce a modified Neel-Brown model that fits the experimental data in which we attribute a T-3/2 dependence to the barrier height and the anisotropy field due to the temperature dependent magnetization and anisotropy energy.

International audience; Using transport measurements and micromagnetic simulations we have investigated the domain wall motion driven by spin-transfer torques in all-perpendicular hexagonal nanopillar spin-valves. In particular, we probe domain walls nucleated in the free layer of the spin-valves, which are then pinned in the devices. We have determined both the field-current state diagrams for the domain-wall state and the thermally activated dynamics of the nucleation and depinning processes. We show that the nucleation process is well-described by a modified Néel-Brown model taking into account the spin-transfer torque, whereas the depinning process is independent of the current. This is confirmed by an analytical calculation which shows that spin-torques have no effect on the Arrhenius escape rate associated with thermally activated domain wall depinning in this geometry. Furthermore, micromagnetic simulations indicate that spin-transfer only weakly affects the domain wall motion, but instead modifies the inner domain wall structure.

We inject current pulses into uniformly magnetized patterns of thin films of the itinerant ferromagnet SrRuO${}_{3}$, while monitoring the effective temperature of the patterns during the current injection. We gradually increase the amplitude of the pulses until magnetization reversal occurs. We observe magnetization reversal induced by current above a temperature-dependent threshold and show that this effect is not simply due to sample heating or Oersted fields. We discuss the applicability of the current-induced spin-wave instability scenario.

International audience; We present a two-current-pulse temporal correlation experiment to study the intrinsic subnanosecond nonequilibrium magnetic dynamics of a nanomagnet during and following a pulse excitation. This method is applied to a model spin-transfer system, a spin-valve nanopillar with perpendicular magnetic anisotropy. Two pulses separated by a short delay (

International audience; The spin-torque switching of metallic nanopillar spin valves showing strong perpendicular anisotropy are studied. The magnetic states of the layers depend on extrinsic parameters such as the magnetic field and the dc current applied to the device. A state diagram presents a comprehensive graph of the role of those parameters on the spin-valve magnetic response. After explaining how state diagrams can be built and the different possible representation, experimental state diagrams are studied for perpendicular devices and the influence of lateral size, temperature, and field orientation are shown. An analytical model of a purely uniaxial system is presented. It is shown that this simple model does not properly reflect the experimental results, whereas if the symmetry is broken a qualitative agreement is obtained. Finally, the possible origins of the symmetry break are discussed in light of an analytical model and numerical simulations.

Spin-Transfer Magnetic Random Access Memory (ST-MRAM) devices hold great promise as a universal memory [Katine 2008]. ST-MRAM is non-volatile, has a small cell size, high endurance and may match the speed of SRAM. A disadvantage of the common collinearly magnetized ST-MRAM is their non-deterministic switching process, which leads to long switching times and broad switching time distributions [Devolder 2008, Koch 2004]. This delay is due to the fact that the torque is zero if the layers are either parallel or antiparallel [Slonczewski 1996] and hence switching cannot be initiated by the torque alone. Typically the process is started by an initial misalignment of the free layer stemming from thermal excitations. Relying on thermal initiation leads to incoherent reversal with an unpredictable incubation delay in the ns range [Devolder 2008] and broad switching time distributions [Koch 2004]

The effect of thermal fluctuations on spin-transfer switching has been studied for a broad range of time scales (sub-ns to seconds) in a model system, a uniaxial thin film nanomagnet. The nanomagnet is incorporated into a spin-valve nanopillar, which is subject to spin-polarized current pulses of variable amplitude and duration. Two physical regimes are clearly distinguished: a long pulse duration regime, in which reversal occurs by spin-transfer assisted thermal activation over an energy barrier, and a short time large pulse amplitude regime, in which the switching probability is determined by the spin angular momentum in the current pulse., 4 page, 3 figures

Spin-transfer devices that have perpendicularly magnetized free and polarizing layers offer the potential for reduced critical currents while still maintaining a high energy barrier U towards thermally induced magnetization reversal. A macrospin [1,2] model predicts a zero-temperature switching current I c0 ∞ U for perpendicularly magnetized devices. In contrast, for in-plane devices the current is increased by a term stemming from the free layer demagnetizing field caused by the free layer magnetization moving out of the plane during the switching process: I c0 ∞ U + μ 0 M2 s V/4.

In this paper, we report on domain wall (DW) motion induced by current pulses at variable temperature in 900 nm wide and 25 nm thick Ni80Fe20 wires with low pinning fields. By using Ar ion milling to pattern our wires rather than the conventional lift-off technique, a depinning field as low as ∼2–3 Oe at room temperature is obtained. Comparison with previous results acquired on similar wires with much higher pinning shows that the critical current density scales with the depinning field, leading to a critical current density of ∼2.5 × 1011 A m−2 at 250 K. Moreover, when a current pulse with a current density larger than the critical current density is injected, the DW is not necessarily depinned but it can undergo a modification of its spin structure which hinders current-induced DW motion. Hence, reliable propagation of the DW requires an accurate adjustment of the pulsed current density.

The stability of 2pi domain walls in ferromagnetic nanorings is investigated via calculation of the minimum energy path that separates a 2pi domain wall from the vortex state of a ferromagnetic nanoring. Trapped domains are stable when they exist between certain types of transverse domain walls, i.e., walls in which the edge defects on the same side of the magnetic strip have equal sign and thus repel. Here the energy barriers between these configurations and vortex magnetization states are obtained using the string method. Due to the geometry of a ring, two types of 2pi walls must be distinguished that differ by their overall topological index and exchange energy. The minimum energy path corresponds to the expulsion of a vortex. The energy barrier for annihilation of a 2pi wall is compared to the activation energy for transitions between the two ring vortex states., Comment: 4 pages, 2 figures

Spin-transfer devices that incorporate a polarizer with its magnetization orthogonal to a switchable (free) layer offer the potential for ultra-fast switching, low power consumption and reliable operation. The non-collinear magnetizations lead to large initial spin-transfer torques, eliminating the incubation delay seen in devices with collinear magnetization. Here we present the basic electrical and magnetic characteristics of spin-valve nanopillars that incorporate a perpendicularly magnetized polarizer and demonstrate current-induced switching with short current pulses, down to 100 ps in duration. We have fabricated devices that have a CoNi polarizer with perpendicular magnetization and an in-plane magnetized 3 nm thick Co free layer and a 12 nm thick Co reference layer, each separated by thin (~ 10 nm) Cu layers. The magnetization of the reference layer is collinear with that of free layer to read out the device state. The reference layer also contributes to the spin-accumulation acting on the free layer and leads to a spin-torque that favors the parallel (P) or antiparallel (AP) state depending on the current pulse polarity, reducing the requirement of precise pulse timing in precessional reversal. The anisotropy field of the perpendicular polarizer is 1.3 T, i.e. it is high enough so that in-plane fields (< 0.3 T) applied to switch the magnetizations of the reference and free layers do not reorient the polarizer. Our typical nanopillar device lateral dimensions are between 60 nm and 300 nm and nanopillars are positioned on coplanar waveguides to allow for broadband electrical connections and studies with fast rise time pulses, generated by an arbitrary waveform generator. The switching probability has been determined for variable pulse amplitude and duration, from 0.1 to 10 ns at room temperature.

In a combined theoretical and experimental study, we investigate the critical current densities for vortex domain walls in magnetic nanowires. We systematically determine the critical current densities for continuous motion of vortex walls as a function of the wire width for different wire thicknesses and we find that the critical current density increases monotonously with decreasing wire width. Theoretically we present a mechanism that predicts a threshold current density based on wall transformations and this leads to a scaling of the critical current density ${j}_{c}\ensuremath{\propto}1/\text{width}$. The origin of this scaling is found to be the different dependence of the spin torque energy and the vortex nucleation energy on the wire width and good agreement with the experimental observations is found.

Using microwave currents, we excite resonances of geometrically confined pinned domain walls, detecting the resonance by the rectification of the microwave current. By applying magnetic fields, the resonance frequency of the domain wall oscillator can be tuned over a wide range. Increasing the power leads to a redshift due to the nonlinearity of the system. From this frequency shift, we directly deduce the quantitative shape of the potential, so that a complete characterization of the pinning potential is obtained.

In this article, a comprehensive study of head-to-head domain wall spin structures in Ni80Fe20 and Co nanostructures is presented. Quantitative domain wall type phase diagrams for NiFe and Co are obtained and compared with available theoretical predictions and micromagnetic simulations. Differences to the experiment are explained taking into account thermal excitations. Thermally induced domain wall type transformations are observed from which a vortex core nucleation barrier height is obtained. The stray field of a domain wall is mapped directly with sub-10nm resolution using off-axis electron holography, and the field intensity is found to decrease as 1/r with distance. The magnetic dipolar coupling of domain walls in NiFe and Co elements is studied using X-ray magnetic circular dicroism photoemission electron microscopy. We observe that the spin structures of interacting domain walls change from vortex to transverse walls, when the distance between the walls is reduced. Using the measured stray field values, the energy barrier height distribution for the nucleation of a vortex core is obtained.

Magnetic domain walls are found to exhibit quasiparticle behavior when subjected to geometrical variations. Because of the spin torque effect such a quasiparticle in a potential well is excited by an ac current leading to a dip in the depinning field at resonance for current densities as low as 2 x 10 power 10 A/m power 2. Independently the resonance frequencies of transverse walls and vortex walls are determined from the dc voltage that develops due to a rectifying effect of the resonant domain wall oscillation. The dependence on the injected current density reveals a strongly nonharmonic oscillation.

We present an experimental study of domain wall motion induced by current pulses as well as by conventional magnetic fields at temperatures between 2 and 300 K in a 110 nm wide and 34 nm thick Ni80Fe20 ring. We observe that, in contrast with field-induced domain wall motion, which is a thermally activated process, the critical current density for current-induced domain wall motion increases with increasing temperature, which implies a reduction of the spin torque efficiency. The effect of Joule heating due to the current pulses is measured and taken into account to obtain critical fields and current densities at constant sample temperatures. This allows for a comparison of our results with theory.

Multi-beam coupling in photorefractive crystals is an attractive method for transferring the energy of several coherent pump beams into a single signal beam. In this process, a spatially periodic intensity pattern is created by interfer-ence of the coherent writing beams. This periodicity allows the de?nition of a two-dimensional elementary cell within the plane of interaction, which is de?ned by the crystal's c-axis and the wave vectors of the beams. Using a single-center model, the temporal evolution of the carrier distribution and the electric ?eld in this elementary cell can be computed numerically, thereby overcoming limitations of the one-dimensional approach used for the description of two beam coupling. The amplitudes and phase shifts of the induced index gratings are then obtained by Fast Fourier Transformation of the local variations of the components of the dielectric tensor caused by the electro-optic effect.

Équipe 101 : Nanomagnétisme et électronique de spin; International audience; We present a study of the temperature dependence of the switching fields in Co/Ni-based perpendicularly magnetized spin-valves. While magnetization reversal of all-perpendicular Co/Ni spin valves at ambient temperatures is typically marked by a single sharp step change in resistance, low temperature measurements can reveal a series of resistance steps, consistent with non-uniform magnetization configurations. We propose a model that consists of domain nucleation, propagation, and annihilation to explain the temperature dependence of the switching fields. Interestingly, low temperature (

Single-shot time-resolved resistance measurements have been used to determine the magnetization reversal mechanisms of orthogonal spin transfer magnetic random access memory (OST-MRAM) devices at nanosecond time scales. There is a strong asymmetry between antiparallel (AP) to parallel (P) and P to AP transitions under the same pulse conditions. P to AP transitions are shown to occur by precession of the free layer magnetization, while the AP to P transition is typically direct, occurring in less than 200 ps. We associate the asymmetry with spin torques perpendicular to the plane of the free layer, an important characteristic of OST-MRAM bit cells that can be used to optimize device performance.

We report on a software-defined digitally configurable measurement platform for determining electronic transport properties in nanostructures with small readout signals. By using a high-resolution audio analog-to-digital/digital-to-analog converter in a digitally compensated bridge configuration we significantly increase the measurement speed compared to established techniques and simultaneously acquire large and small signal characteristics. We characterize the performance (16 bit resolution, 100 dB dynamic range at 192 kS/s) and demonstrate the application of this measurement platform for studying the transport properties of spin-valve nanopillars, a two-terminal device that exhibits giant magnetoresistance and whose resistance can be switched between two levels by applied magnetic fields and by currents applied by the audio card. The high resolution and fast sampling capability permits rapid acquisition of deep statistics on the switching of a spin-valve nanopillar and reduces the time to acquire the basic properties of the device - a state-diagram showing the magnetic configurations as function of applied current and magnetic field - by orders of magnitude.

Ferromagnetic resonance spectroscopy is used to determine magnetic interactions in layer stacks designed for orthogonal spin-transfer magnetic random memory devices. The stacks have layers with different anisotropy directions and coupling, consisting of a perpendicularly magnetized polarizer, an in-plane magnetized free layer, and an in-plane magnetized exchange biased synthetic antiferromagnetic layer. The oscillatory exchange coupling strength in the synthetic antiferromagnet was measured along with its exchange bias. The free layer properties were also determined. It is demonstrated that this one integrated measurement technique is able to provide quantitative measurements of key magnetic parameters in a complex layer stack, which is a prerequisite for high turn-around device materials characterization and optimization.

We report the free layer switching field distributions of spin-valve nanopillars with perpendicular magnetization. While the distributions are consistent with a thermal activation model, they show a strong asymmetry between the parallel to antiparallel and the reverse transition, with energy barriers more than 50% higher for the parallel to antiparallel transitions. The inhomogeneous dipolar field from the polarizer is demonstrated to be at the origin of this symmetry breaking. Interestingly, the symmetry is restored for devices with a lithographically defined notch pair removed from the midpoint of the pillar cross-section along the ellipse long axis. These results have important implications for the thermal stability of perpendicular magnetized MRAM bit cells., Comment: Submitted to Applied Physics Letters on November 4, 2011. Consists of 4 pages, 3 figures

Orthogonal spin-transfer magnetic random access memory (OST-MRAM) uses a spin-polarizing layer magnetized perpendicularly to a free layer to achieve large spin-transfer torques and ultrafast energy efficient switching. We have fabricated and studied OST-MRAM devices that incorporate a perpendicularly magnetized spin-polarizing layer and a magnetic tunnel junction, which consists of an in-plane magnetized free layer and synthetic antiferromagnetic reference layer. Reliable switching is observed at room temperature with 0.7 V amplitude pulses of 500 ps duration. The switching is bipolar, occurring for positive and negative polarity pulses, consistent with a precessional reversal mechanism, and requires an energy of less than 450 fJ.