3,256 research outputs found
Macromagnetic simulation for reservoir computing utilizing spin dynamics in magnetic tunnel junctions
The figures-of-merit for reservoir computing (RC), using spintronics devices
called magnetic tunnel junctions (MTJs), are evaluated. RC is a type of
recurrent neural network. The input information is stored in certain parts of
the reservoir, and computation can be performed by optimizing a linear
transform matrix for the output. While all the network characteristics should
be controlled in a general recurrent neural network, such optimization is not
necessary for RC. The reservoir only has to possess a non-linear response with
memory effect. In this paper, macromagnetic simulation is conducted for the
spin-dynamics in MTJs, for reservoir computing. It is determined that the
MTJ-system possesses the memory effect and non-linearity required for RC. With
RC using 5-7 MTJs, high performance can be obtained, similar to an echo-state
network with 20-30 nodes, even if there are no magnetic and/or electrical
interactions between the magnetizations
Ultra-Fast Ferrimagnetic All Spin Logic Device
All spin logic device (ASLD) blazes an alternative path for realizing
ultra-low power computing in the Post-Moore era. However, initial device
structure relying on ferromagnetic input/output and spin transfer torque (STT)
driven magnetization switching degrades its performance and even hinders its
realization. In this paper, we propose an ASLD based on rare-earth
(RE)-transition-metal (TM) ferromagnetic alloy that can achieve an ultra-high
frequency up to terahertz. The spin orbit torque (SOT) induced fast precession
near the spin angular momentum compensated point is investigated through the
macrospin model. Combining the non-local spin current diffusing from the input
to the output, a deterministic picosecond switching can be realized without any
external magnetic field. Our results show that ASLD has the potential to exceed
the performance of mainstream computing
Experimental demonstration of a Josephson magnetic memory cell with a programmable \pi-junction
We experimentally demonstrate the operation of a Josephson magnetic random
access memory unit cell, built with a Ni_80Fe_20/Cu/Ni pseudo spin-valve
Josephson junction with Nb electrodes and an integrated readout SQUID in a
fully planarized Nb fabrication process. We show that the parallel and
anti-parallel memory states of the spin-valve can be mapped onto a junction
equilibrium phase of either zero or pi by appropriate choice of the ferromagnet
thicknesses, and that the magnetic Josephson junction can be written to either
a zero-junction or pi-junction state by application of write fields of
approximately 5 mT. This work represents a first step towards a scalable,
dense, and power-efficient cryogenic memory for superconducting
high-performance digital computing.Comment: 5 pages, 5 figures, accepted by IEEE Magnetics Letter
Circuit Theory for SPICE of Spintronic Integrated Circuits
We present a theoretical and a numerical formalism for analysis and design of
spintronic integrated circuits (SPINICs). The formalism encompasses a
generalized circuit theory for spintronic integrated circuits based on
nanomagnetic dynamics and spin transport. We propose an extension to the
Modified Nodal Analysis technique for the analysis of spin circuits based on
the recently developed spin conduction matrices. We demonstrate the
applicability of the framework using an example spin logic circuit described
using spin Netlists.Comment: 14 pages, 11 figures; added fig. 2; added citations; modified title
to emphasize SPICE; Results unchange
Fast magneto-ionic switching of interface anisotropy using yttria-stabilized zirconia gate oxide
Voltage control of interfacial magnetism has been greatly highlighted in
spintronics research for many years, as it might enable ultra-low power
technologies. Among few suggested approaches, magneto-ionic control of
magnetism has demonstrated large modulation of magnetic anisotropy. Moreover,
the recent demonstration of magneto-ionic devices using hydrogen ions presented
relatively fast magnetization toggle switching, tsw ~ 100 ms, at room
temperature. However, the operation speed may need to be significantly improved
to be used for modern electronic devices. Here, we demonstrate that the speed
of proton-induced magnetization toggle switching largely depends on
proton-conducting oxides. We achieve ~1 ms reliable (> 103 cycles) switching
using yttria-stabilized zirconia (YSZ), which is ~ 100 times faster than the
state-of-the-art magneto-ionic devices reported to date at room temperature.
Our results suggest further engineering of the proton-conducting materials
could bring substantial improvement that may enable new low-power computing
scheme based on magneto-ionics.Comment: 19 pages, 3 figures - published in Nano Letter
A hands-on laboratory and computational experience for nanoscale materials, devices and systems education for electronics, spintronics and optoelectronics
To enhance the undergraduate and graduate engineering education for nanoscale
materials, devices and systems, we report a multi-disciplinary course based on
the integration of theory, hands-on laboratory and hands-on computation into a
single curriculum. The hands-on laboratory modules span various
dimensionalities of nanomaterials as well as applications in logic, memory, and
energy harvesting. In the hands-on computational exercises, students simulate
the material and the device characteristics, and in some cases, design the
experimental process flow to fabricate and characterize the devices and
systems. Such a course not only grooms the students for multi-disciplinary
collaborative activities in nanoscience and nanoengineering, but also prepares
them well for future academic or industrial pursuit in this area.Comment: 13 pages, 5 figures and 1 tabl
Spintronics based Stochastic Computing for Efficient Bayesian Inference System
Bayesian inference is an effective approach for solving statistical learning
problems especially with uncertainty and incompleteness. However, inference
efficiencies are physically limited by the bottlenecks of conventional
computing platforms. In this paper, an emerging Bayesian inference system is
proposed by exploiting spintronics based stochastic computing. A stochastic
bitstream generator is realized as the kernel components by leveraging the
inherent randomness of spintronics devices. The proposed system is evaluated by
typical applications of data fusion and Bayesian belief networks. Simulation
results indicate that the proposed approach could achieve significant
improvement on inference efficiencies in terms of power consumption and
inference speed.Comment: accepted by ASPDAC 2018 conferenc
Perspective: Ultrafast magnetism and THz spintronics
This year the discovery of femtosecond demagnetization by laser pulses is 20
years old. For the first time this milestone work by Bigot and coworkers gave
insight in a very direct way into the time scales of microscopic interactions
that connect the spin and electron system. While intense discussions in the
field were fueled by the complexity of the processes in the past, it now became
evident that it is a puzzle of many different parts. Rather than giving an
overview that has been presented in previous reviews on ultrafast processes in
ferromagnets, this perspective will show that with our current depth of
knowledge the first real applications are on their way: THz spintronics and
all-optical spin manipulation are becoming more and more feasible. The aim of
this perspective is to point out where we can connect the different puzzle
pieces of understanding gathered over 20 years to develop novel applications.
based on many observations in a large number of experiments. Differences in the
theoretical models arise from the localized and delocalized nature of
ferromagnetism. Transport effects are intrinsically non-local in spintronic
devices and at interfaces. We review the need for multiscale modeling to
address processes starting from electronic excitation of the spin system on the
picometer length scale and sub-femtosecond time scale, to spin wave generation,
and towards the modeling of ultrafast phase transitions that altogether
determine the response time of the ferromagnetic system. Today, our current
understanding gives rise to the first real applications of ultrafast spin
physics for ultrafast magnetism control: THz spintronic devices. This makes the
field of ultrafast spin-dynamics an emerging topic open for many researchers
right now.Comment: 24 pages, 11 figures, revie
p-Bits for Probabilistic Spin Logic
We introduce the concept of a probabilistic or p-bit, intermediate between
the standard bits of digital electronics and the emerging q-bits of quantum
computing. We show that low barrier magnets or LBM's provide a natural physical
representation for p-bits and can be built either from perpendicular magnets
(PMA) designed to be close to the in-plane transition or from circular in-plane
magnets (IMA). Magnetic tunnel junctions (MTJ) built using LBM's as free layers
can be combined with standard NMOS transistors to provide three-terminal
building blocks for large scale probabilistic circuits that can be designed to
perform useful functions. Interestingly, this three-terminal unit looks just
like the 1T/MTJ device used in embedded MRAM technology, with only one
difference: the use of an LBM for the MTJ free layer. We hope that the concept
of p-bits and p-circuits will help open up new application spaces for this
emerging technology. However, a p-bit need not involve an MTJ, any fluctuating
resistor could be combined with a transistor to implement it, while completely
digital implementations using conventional CMOS technology are also possible.
The p-bit also provides a conceptual bridge between two active but disjoint
fields of research, namely stochastic machine learning and quantum computing.
First, there are the applications that are based on the similarity of a p-bit
to the binary stochastic neuron (BSN), a well-known concept in machine
learning. Three-terminal p-bits could provide an efficient hardware accelerator
for the BSN. Second, there are the applications that are based on the p-bit
being like a poor man's q-bit. Initial demonstrations based on full SPICE
simulations show that several optimization problems including quantum annealing
are amenable to p-bit implementations which can be scaled up at room
temperature using existing technology
High-Resolution X-Ray Studies of the Direct Spin Contact of EuO with Silicon
Ferromagnetic semiconductor europium monoxide (EuO) is believed to be an
effective spin injector when directly integrated with silicon. Injection
through spin-selective ohmic contact requires superb structural quality of the
interface EuO/Si. Recent breakthrough in manufacturing free-of-buffer-layer
EuO/Si junctions calls for structural studies of the interface between the
semiconductors. Ex situ high-resolution X-ray diffraction and reflectivity
accompanied by in situ reflection high-energy electron diffraction reveal
direct coupling at the interface. A combined analysis of XRD and XRR data
provides a common structural model. The structural quality of the EuO/Si spin
contact by far exceeds that of previous reports and thus makes a step forward
to the ultimate goals of spintronics
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