1,675 research outputs found
Switching dynamics of a magnetostrictive single-domain nanomagnet subjected to stress
The temporal evolution of the magnetization vector of a single-domain
magnetostrictive nanomagnet, subjected to in-plane stress, is studied by
solving the Landau-Lifshitz-Gilbert equation. The stress is ramped up linearly
in time and the switching delay, which is the time it takes for the
magnetization to flip, is computed as a function of the ramp rate. For high
levels of stress, the delay exhibits a non-monotonic dependence on the ramp
rate, indicating that there is an {\it optimum} ramp rate to achieve the
shortest delay. For constant ramp rate, the delay initially decreases with
increasing stress but then saturates showing that the trade-off between the
delay and the stress (or the energy dissipated in switching) becomes less and
less favorable with increasing stress. All of these features are due to a
complex interplay between the in-plane and out-of-plane dynamics of the
magnetization vector induced by stress
Statistical mechanics of ecosystem assembly
We introduce a toy model of ecosystem assembly for which we are able to map
out all assembly pathways generated by external invasions. The model allows to
display the whole phase space in the form of an assembly graph whose nodes are
communities of species and whose directed links are transitions between them
induced by invasions. We characterize the process as a finite Markov chain and
prove that it exhibits a unique set of recurrent states (the endstate of the
process), which is therefore resistant to invasions. This also shows that the
endstate is independent on the assembly history. The model shares all features
with standard assembly models reported in the literature, with the advantage
that all observables can be computed in an exact manner.Comment: Accepted for publication in Physical Review Letter
Hybrid spintronics and straintronics: A magnetic technology for ultra low energy computing and signal processing
The authors show that the magnetization of a 2-phase magnetostrictive/piezoelectric multiferroic single-domain shape-anisotropic nanomagnet can be switched with very small voltages that generate strain in the magnetostrictive layer. This can be the basis of ultralow power computing and signal processing. With appropriate material choice, the energy dissipated per switching event can be reduced to ∼45 kT at room temperature for a switching delay of ∼100 ns and ∼70 kT for a switching delay of ∼10 ns, if the energy barrier separating the two stable magnetization directions is ∼32 kT. Such devices can be powered by harvesting energy exclusively from the environment without the need for a battery
Bed-load discharge measurement by ADCP in actual rivers
River engineeringInnovative field and laboratory instrumentatio
Magnetic domain-wall creep driven by field and current in Ta/CoFeB/MgO
Creep motion of magnetic domain wall (DW), thermally activated DW dynamics under subthreshold driving forces, is a paradigm to understand the interaction between driven interfaces and applied external forces. Previous investigation has shown that DW in a metallic system interacts differently with current and magnetic field, manifesting itself as different universality classes for the creep motion. In this article, we first review the experimental determination of the universality classes for current- and field-driven DW creeps in a Ta/CoFeB/MgO wire, and then elucidate the underlying factors governing the obtained results. We show that the nature of torque arising from current in association with DW configuration determines universality class for the current-induced creep in this system. We also discuss the correlation between the field-induced DW creep characteristics and structure observed by a transmission electron microscope. The observed results are expected to provide a deeper understanding for physics of DW motion in various magnetic materials
Magnetic order in nanoscale gyroid networks
Three-dimensional magnetic metamaterials feature interesting phenomena that
arise from a delicate interplay of material properties, local anisotropy,
curvature, and connectivity. A particularly interesting magnetic lattice that
combines these aspects is that of nanoscale gyroids, with a
highly-interconnected chiral network with local three-connectivity reminiscent
of three-dimensional artificial spin ices. Here, we use finite-element
micromagnetic simulations to elucidate the anisotropic behaviour of nanoscale
nickel gyroid networks at applied fields and at remanence. We simplify the
description of the micromagnetic spin states with a macrospin model to explain
the anistropic global response, to quantify the extent of ice-like
correlations, and to discuss qualitative features of the anisotropic
magnetoresistance in the three-dimensional network. Our results demonstrate the
large variability of the magnetic order in extended gyroid networks, which
might enable future spintronic functionalities, including neuromorphic
computing and non-reciprocal transport.Comment: 10 pages, 6 figure
Recuperação e sobrevivência de Bradyrhizobium em sementes de soja tratadas com fungicidas e inseticidas.
O processo de fixação biológica do nitrogênio (FBN) representa um componente essencial para a viabilidade econômica da cultura da soja. No entanto, para um processo eficiente, um número mínimo de células viáveis de Bradyrhizobium deve estar presente para o estabelecimento da simbiose e o uso concomitante de produtos químicos, como inseticidas e fungicidas, pode comprometer a viabilidade das células. Neste estudo, foram avaliadas novas combinações de inoculantes e polímeros na presença de tratamento de sementes com fungicidas e inseticidas, em tratamento manual ou industrial. Foi constatado que novas formulações e aplicações de produtos nas sementes podem permitir a pré-inoculação por até 4 dias, considerando a sobrevivência de pelo menos 10 5 células/semente
Layer thickness dependence of the current induced effective field vector in Ta|CoFeB|MgO
The role of current induced effective magnetic field in ultrathin magnetic
heterostructures is increasingly gaining interest since it can provide
efficient ways of manipulating magnetization electrically. Two effects, known
as the Rashba spin orbit field and the spin Hall spin torque, have been
reported to be responsible for the generation of the effective field. However,
quantitative understanding of the effective field, including its direction with
respect to the current flow, is lacking. Here we show vector measurements of
the current induced effective field in Ta|CoFeB|MgO heterostructrures. The
effective field shows significant dependence on the Ta and CoFeB layers'
thickness. In particular, 1 nm thickness variation of the Ta layer can result
in nearly two orders of magnitude difference in the effective field. Moreover,
its sign changes when the Ta layer thickness is reduced, indicating that there
are two competing effects that contribute to the effective field. The relative
size of the effective field vector components, directed transverse and parallel
to the current flow, varies as the Ta thickness is changed. Our results
illustrate the profound characteristics of just a few atomic layer thick metals
and their influence on magnetization dynamics
DNA barcoding reveals the coral “laboratory-rat”, Stylophora pistillata encompasses multiple identities
Stylophora pistillata is a widely used coral “lab-rat” species with highly variable morphology and a broad biogeographic range (Red Sea to western central Pacific). Here we show, by analysing Cytochorme Oxidase I sequences, from 241 samples across this range, that this taxon in fact comprises four deeply divergent clades corresponding to the Pacific-Western Australia, Chagos-Madagascar-South Africa, Gulf of Aden-Zanzibar-Madagascar, and Red Sea-Persian/Arabian Gulf-Kenya. On the basis of the fossil record of Stylophora, these four clades diverged from one another 51.5-29.6 Mya, i.e., long before the closure of the Tethyan connection between the tropical Indo-West Pacific and Atlantic in the early Miocene (16–24 Mya) and should be recognised as four distinct species. These findings have implications for comparative ecological and/or physiological studies carried out using Stylophora pistillata as a model species, and highlight the fact that phenotypic plasticity, thought to be common in scleractinian corals, can mask significant genetic variation
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