14,846 research outputs found
Dynamics of coupled vortices in layered magnetic nanodots
The spin dynamics are calculated for a model system consisting of
magnetically soft, layered nanomagnets, in which two ferromagnetic (F)
cylindrical dots, each with a magnetic vortex ground state, are separated by a
non-magnetic spacer (N). This permits a study of the effects of interlayer
magnetostatic interactions on the vortex dynamics. The system was explored by
applying the equations of motion for the vortex core positions. The restoring
force was calculated taking into account the magnetostatic interactions
assuming a realistic surface charge free spin distribution. For tri-layer F/N/F
dots with opposite chiralities and the same core polarizations (lowest energy
state), two eigenmodes are predicted analytically and confirmed via
micromagnetic simulations. One mode is in the sub-GHz range for submicron dot
diameters and corresponds to quasi-circular rotation of the cores about the dot
center. A second mode is in the MHz range corresponding to a small amplitude
rotation of the mean core position. The eigenfrequencies depend strongly on the
geometrical parameters of the system, suggesting that magnetostatic effects
play a dominant role in determining the vortex dynamics.Comment: One PDF file including text and 4 figure
Developing Health Information Literacy in Disadvantaged and Dependent Circumstances: The Everyday Role of Family Nurses
This paper examines the challenges of developing health information literacy (HIL) amongst disadvantaged and dependent populations from the perspective of non-information professionals occupying everyday support roles. Our participants were a team of UK Family Nurses providing outreach support to vulnerable young mothers from areas of multiple deprivations. Our data collection methods were observation, interviews, and focus groups. Our participants all believe that they have an important role in developing HIL in clients but are unfamiliar with fundamental overarching information literacy (IL) concepts and models. Consequently, their confidence in their own ability to develop HIL skills in clients is limited. We discuss that to extend primary healthcare practices beyond HIL support to HIL education requires not only IL training, but also an appropriate pedagogical approach adaptable to semi-structured problematic situations. We raise important questions regarding approaches to developing HIL in disadvantaged population
Magnetic Vortex Resonance in Patterned Ferromagnetic Dots
We report a high-resolution experimental detection of the resonant behavior
of magnetic vortices confined in small disk-shaped ferromagnetic dots. The
samples are magnetically soft Fe-Ni disks of diameter 1.1 and 2.2 um, and
thickness 20 and 40 nm patterned via electron beam lithography onto microwave
co-planar waveguides. The vortex excitation spectra were probed by a vector
network analyzer operating in reflection mode, which records the derivative of
the real and the imaginary impedance as a function of frequency. The spectra
show well-defined resonance peaks in magnetic fields smaller than the
characteristic vortex annihilation field. Resonances at 162 and 272 MHz were
detected for 2.2 and 1.1 um disks with thickness 40 nm, respectively. A
resonance peak at 83 MHz was detected for 20-nm thick, 2-um diameter disks. The
resonance frequencies exhibit weak field dependence, and scale as a function of
the dot geometrical aspect ratio. The measured frequencies are well described
by micromagnetic and analytical calculations that rely only on known properties
of the dots (such as the dot diameter, thickness, saturation magnetization, and
exchange stiffness constant) without any adjustable parameters. We find that
the observed resonance originates from the translational motion of the magnetic
vortex core.Comment: submitted to PRB, 17 pages, 5 Fig
Polarity Reversal of a Magnetic Vortex Core by a Unipolar, Nonresonant In-plane Pulsed Magnetic Field
We report the polarity reversal of a magnetic vortex core using a nonresonant in-plane pulsed magnetic field of arbitrary waveform studied using time-resolved x-ray photoemission electron microscopy and micromagnetic simulations. The imaging and simulations show that a 5 mT pulse, higher than the critical field for nonlinear effects, effectively leads to the randomization of the vortex core polarity. The micromagnetic simulations further show that the onset of stochastic core polarity randomization does not necessarily coincide with the critical reversal field, leading to a field window for predictable core reversal
Polarity Reversal of a Magnetic Vortex Core by a Unipolar, Nonresonant In-plane Pulsed Magnetic Field
We report the polarity reversal of a magnetic vortex core using a nonresonant in-plane pulsed magnetic field of arbitrary waveform studied using time-resolved x-ray photoemission electron microscopy and micromagnetic simulations. The imaging and simulations show that a 5 mT pulse, higher than the critical field for nonlinear effects, effectively leads to the randomization of the vortex core polarity. The micromagnetic simulations further show that the onset of stochastic core polarity randomization does not necessarily coincide with the critical reversal field, leading to a field window for predictable core reversal
Nonlinear Vortex Dynamics and Transient Domains in Ferromagnetic Disks
We report a time-resolved imaging and micromagnetic simulation study of the relaxation dynamics of a magnetic vortex in the nonlinear regime. We use time-resolved photoemission electron microscopy and micromagnetic calculations to examine the emergence of nonlinear vortex dynamics in patterned Ni80Fe20 disks in the limit of long field pulses. We show for core shifts beyond ∼20%–25% of the disk radius, the initial motion is characterized by distortions of the vortex, a transient cross-tie wall state, and instabilities in the core polarization that influence the core trajectories
Nonlinear Vortex Dynamics and Transient Domains in Ferromagnetic Disks
We report a time-resolved imaging and micromagnetic simulation study of the relaxation dynamics of a magnetic vortex in the nonlinear regime. We use time-resolved photoemission electron microscopy and micromagnetic calculations to examine the emergence of nonlinear vortex dynamics in patterned Ni80Fe20 disks in the limit of long field pulses. We show for core shifts beyond ∼20%–25% of the disk radius, the initial motion is characterized by distortions of the vortex, a transient cross-tie wall state, and instabilities in the core polarization that influence the core trajectories
Kinetic pathways of multi-phase surfactant systems
The relaxation following a temperature quench of two-phase (lamellar and
sponge phase) and three-phase (lamellar, sponge and micellar phase) samples,
has been studied in an SDS/octanol/brine system. In the three-phase case we
have observed samples that are initially mainly sponge phase with lamellar and
micellar phase on the top and bottom respectively. Upon decreasing temperature
most of the volume of the sponge phase is replaced by lamellar phase. During
the equilibriation we have observed three regimes of behaviour within the
sponge phase: (i) disruption in the sponge texture, then (ii) after the sponge
phase homogenises there is a lamellar nucleation regime and finally (iii) a
bizarre plume connects the lamellar phase with the micellar phase. The
relaxation of the two-phase sample proceeds instead in two stages. First
lamellar drops nucleate in the sponge phase forming a onion `gel' structure.
Over time the lamellar structure compacts while equilibriating into a two phase
lamellar/sponge phase sample. We offer possible explanatioins for some of these
observations in the context of a general theory for phase kinetics in systems
with one fast and one slow variable.Comment: 1 textfile, 20 figures (jpg), to appear in PR
Similarities of the primary charge seperation in the photosynthesis of Rhodobacter sphaeroides and Rodopseudomanas viridis
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