57 research outputs found
Time-dependent quantum transport and power-law decay of the transient current in a nano-relay and nano-oscillator
Time-dependent nonequilibrium Green's functions are used to study electron
transport properties in a device consisting of two linear chain leads and a
time-dependent interleads coupling that is switched on non-adiabatically. We
derive a numerically exact expression for the particle current and examine its
characteristics as it evolves in time from the transient regime to the
long-time steady-state regime. We find that just after switch-on the current
initially overshoots the expected long-time steady-state value, oscillates and
decays as a power law, and eventually settles to a steady-state value
consistent with the value calculated using the Landauer formula. The power-law
parameters depend on the values of the applied bias voltage, the strength of
the couplings, and the speed of the switch-on. In particular, the oscillating
transient current decays away longer for lower bias voltages. Furthermore, the
power-law decay nature of the current suggests an equivalent series
resistor-inductor-capacitor circuit wherein all of the components have
time-dependent properties. Such dynamical resistive, inductive, and capacitive
influences are generic in nano-circuites where dynamical switches are
incorporated. We also examine the characteristics of the dynamical current in a
nano-oscillator modeled by introducing a sinusoidally modulated interleads
coupling between the two leads. We find that the current does not strictly
follow the sinusoidal form of the coupling. In particular, the maximum current
does not occur during times when the leads are exactly aligned. Instead, the
times when the maximum current occurs depend on the values of the bias
potential, nearest-neighbor coupling, and the interleads coupling.Comment: version accepted for publication in JA
Ultrafast and low-energy switching in voltage-controlled elliptical pMTJ
Switching magnetization in a perpendicular magnetic tunnel junction (pMTJ)
via voltage controlled magnetic anisotropy (VCMA) has shown the potential to
markedly reduce the switching energy. However, the requirement of an external
magnetic field poses a critical bottleneck for its practical applications. In
this work, we propose an elliptical-shaped pMTJ to eliminate the requirement of
providing an external field by an additional circuit. We demonstrate that a 10
nm thick in-plane magnetized bias layer (BL) separated by a metallic spacer of
3 nm from the free layer (FL) can be engineered within the MTJ stack to provide
the 50 mT bias magnetic field for switching. By conducting macrospin
simulation, we find that a fast switching in 0.38 ns with energy consumption as
low as 0.3 fJ at a voltage of 1.6 V can be achieved. Furthermore, we study the
phase diagram of switching probability, showing that a pulse duration margin of
0.15 ns is obtained and a low-voltage operation (~ 1 V) is favored. Finally,
the MTJ scalability is considered, and it is found that scaling-down may not be
appealing in terms of both the energy consumption and the switching time for
the precession based VCMA switching.Comment: There are 28 pages and 5 figure
Spin-wave mediated interactions for Majority Computation using Skyrmions and Spin-torque Nano-oscillators
Recent progress in all-electrical nucleation, detection and manipulation of
magnetic skyrmions has unlocked the tremendous potential of skyrmion-based
spintronic devices. Here, we show via micromagnetic simulations that the stable
magnetic oscillations of STNO radiate spin waves (SWs) that can be scattered in
the presence of skyrmions in the near vicinity. Interference between SWs
emitted by the STNO and SWs scattered by the skyrmion gives rise to interesting
dynamics that leads to amplification or attenuation of STNO's magnetic
oscillations. In the presence of strong Dzyaloshinskii-Moriya interaction
(DMI), the amplified magnetic oscillations evolve into a new skyrmion. These
interactions between skyrmions and STNOs are found to be identical for both
Neel-type and Bloch-type skyrmions, and are not observed between domain walls
and STNOs. These findings offer a novel perspective in processing information
using single skyrmions and we propose a 3-bit majority gate for logic
applications.Comment: Final Versio
Electric-field-induced Three-terminal pMTJ Switching in the absence of an External Magnetic Field
Since it is undesirable to require an external magnetic field for on-chip
memory applications, we investigate the use of a Rashba effective field
alternatively for assisting the electric-field-induced switching operation of a
three terminal perpendicular magnetic tunnel junction (pMTJ). By conducting
macro-spin simulation, we show that a pMTJ with thermal stability of 61 can be
switched in 0.5 ns consuming a switching energy of 6 fJ, and the voltage
operation margin can be improved to 0.8 ns. Furthermore, the results also
demonstrate that a heavy metal system that can provide large field-like torque
rather than damping-like torque is favored for the switching.Comment: there are 10 pages and 5 figures in this fil
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