-Spin-wave interference patterns created by spin-torque nano-oscillators for memory and computation, F. Macia, A. D. Kent and F. Hoppenstead, Nanotechnology 22, 095301 (2011).
Magnetization dynamics in nanomagnets has attracted broad interest since it was predicted that a dc current flowing through a thin magnetic layer can create spin-wave excitations. These excitations are due to spin momentum transfer, a transfer of spin angular momentum between conduction electrons and the background magnetization, that enables new types of information processing. Here we show how arrays of spin-torque nano-oscillators can create propagating spin-wave interference patterns of use for memory and computation. Memristic transponders distributed on the thin film respond to threshold tunnel magnetoresistance values, thereby allowing spin-wave detection and creating new excitation patterns. We show how groups of transponders create resonant (reverberating) spin-wave interference patterns that may be used for polychronous wave computation and information storage.
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-Ultrafast switching in magnetic tunnel junction based orthogonal spin transfer devices, H. Liu, D. Bedau, D. Backes, J. A. Katine, J. Langer and A. D. Kent, Applied Physics Letters 97, 242510 (2010).
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.
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-Spin-transfer pulse switching: From the dynamic to the thermally activated regime, D. Bedau, H. Liu, J. Z. Sun, J. A. Katine, E. E. Fullerton, S. Mangin and A. D. Kent, Applied Physics Letters 97, 262502 (2010).
The effect of thermal fluctuations on spin-transfer switching has been studied for a broad range of time scales (ubnanoseconds 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.
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-Perpendicular all the way, A. D. Kent, Nature Materials 9, 699 (2010): News and Views Article on new type of Spin Transfer Torque Magnetic Random Access Memory (STT-MRAM).
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-Pure and random-field quantum criticality in the dipolar Ising model: Theory of Mn12 acetates, A. J. Millis, A. D. Kent, M. P. Sarachik, and Y. Yeshurun, Physical Review B 82, 014406 (2010).
A theoretical model for the Mn12 acetates is derived including a "random-field" effect arising from isomer effects in some families of host acetate materials. Estimates for the important energy scales are given. Phase boundaries are determined using a mean-field approximation. Predictions for experiment are presented.
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