290 research outputs found
Multiple Avalanches Across the Metal-Insulator Transition of Vanadium Oxide Nano-scaled Junctions
The metal insulator transition of nano-scaled devices is drastically
different from the smooth transport curves generally reported. The temperature
driven transition occurs through a series of resistance jumps ranging over 2
decades in amplitude, indicating that the transition is caused by avalanches.
We find a power law distribution of the jump amplitudes, demonstrating an
inherent property of the films. We report a surprising relation between
jump amplitude and device size. A percolation model captures the general
transport behavior, but cannot account for the statistical behavior.Comment: 4 papers and 4 figures submitted to PR
A caloritronics-based Mott neuristor
Machine learning imitates the basic features of biological neural networks to
efficiently perform tasks such as pattern recognition. This has been mostly
achieved at a software level, and a strong effort is currently being made to
mimic neurons and synapses with hardware components, an approach known as
neuromorphic computing. CMOS-based circuits have been used for this purpose,
but they are non-scalable, limiting the device density and motivating the
search for neuromorphic materials. While recent advances in resistive switching
have provided a path to emulate synapses at the 10 nm scale, a scalable neuron
analogue is yet to be found. Here, we show how heat transfer can be utilized to
mimic neuron functionalities in Mott nanodevices. We use the Joule heating
created by current spikes to trigger the insulator-to-metal transition in a
biased VO2 nanogap. We show that thermal dynamics allow the implementation of
the basic neuron functionalities: activity, leaky integrate-and-fire,
volatility and rate coding. By using local temperature as the internal
variable, we avoid the need of external capacitors, which reduces neuristor
size by several orders of magnitude. This approach could enable neuromorphic
hardware to take full advantage of the rapid advances in memristive synapses,
allowing for much denser and complex neural networks. More generally, we show
that heat dissipation is not always an undesirable effect: it can perform
computing tasks if properly engineered
Deconvoluting Reversal Modes in Exchange Biased Nanodots
Ensemble-averaged exchange bias in arrays of Fe/FeF2 nanodots has been
deconvoluted into local, microscopic, bias separately experienced by nanodots
going through different reversal modes. The relative fraction of dots in each
mode can be modified by exchange bias. Single domain dots exhibit a simple loop
shift, while vortex state dots have asymmetric shifts in the vortex nucleation
and annihilation fields, manifesting local incomplete domain walls in these
nanodots as magnetic vortices with tilted cores.Comment: 17 pages, 3 figures. Phys. Rev. B in pres
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Acquisition of an In-House X-ray Scattering Facility for Nanostructure Characterization and Student Training
This equipment grant was specifically dedicated to the development of a "state of the art" x-ray scattering facility..
Dynamics of Spontaneous Magnetization Reversal in Exchange Biased Heterostructures
The dependence of thermally induced spontaneous magnetization reversal on
time-dependent cooling protocols was studied. Slower cooling and longer waiting
close to the N\`{e}el temperature of the antiferromagnet () enhances the
magnetization reversal. Cycling the temperature around leads to a thermal
training effect under which the reversal magnitude increases with each cycle.
These results suggest that spontaneous magnetization reversal is energetically
favored, contrary to our present understanding of positive exchange bias
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