3,483 research outputs found
Magnonic crystal based forced dominant wavenumber selection in a spin-wave active ring
Spontaneous excitation of the dominant mode in a spin-wave active ring -- a
self-exciting positive-feedback system incorporating a spin-wave transmission
structure -- occurs at a certain threshold value of external gain. In general,
the wavenumber of the dominant mode is extremely sensitive to the properties
and environment of the spin-wave transmission medium, and is almost impossible
to predict. In this letter, we report on a backward volume magnetostatic
spin-wave active ring system incorporating a magnonic crystal. When mode
enhancement conditions -- readily predicted by a theoretical model -- are
satisfied, the ring geometry permits highly robust and consistent forced
dominant wavenumber selection.Comment: 4 pages, 3 figure
Origin of Ferroelastic Domains in Free-Standing Single Crystal Ferroelectric Films
The origin of the unusual 90^o ferroelectric / ferroelastic domains,
consistently observed in recent studies on meso and nanoscale free-standing
single crystals of BaTiO3 [Schilling et al., Physical Review B, 74, 024115
(2006); Schilling et al., Nano Letters, 7, 3787 (2007)], has been considered. A
model has been developed which postulates that the domains form as a response
to elastic stress induced by a surface layer which does not undergo the
paraelectric-ferroelectric, cubic-tetragonal phase transition. This model was
found to accurately account for the changes in domain periodicity as a function
of size that had been observed experimentally. The physical origin of the
surface layer might readily be associated with patterning damage, seen in
experiment; however, when all evidence of physical damage is removed from the
BaTiO3 surfaces by thermal annealing, the domain configuration remains
practically unchanged. This suggests a more intrinsic origin, such as the
increased importance of surface tension at small dimensions. The effect of
surface tension is also shown to be proportional to the difference in hardness
between the surface and the interior of the ferroelectric. The present model
for surface tension induced twinning should also be relevant for finely grained
or core-shell structured ceramics
Superdomain dynamics in ferroelectric-ferroelastic films: Switching, jamming, and relaxation
Recent experimental work shows that ferroelectric switching can occur in large jumps in which ferroelastic superdomains switch together, rather than having the numerous smaller ferroelectric domains switch within them. In this sense, the superdomains play a role analogous to that of Abrikosov vortices in thin superconducting films under the Kosterlitz-Thouless framework, which control the dynamics more than individual Cooper pairs within them do. Here, we examine the dynamics of ferroelastic superdomains in ferroelastic ferroelectrics and their role in switching devices such as memories. Jamming of ferroelectric domains in thin films has revealed an unexpected time dependence of t-1/4 at long times (hours), but it is difficult to discriminate between power-law and exponential relaxation. Other aspects of this work, including spatial period doubling of domains, led to a description of ferroelastic domains as nonlinear processes in a viscoelastic medium, which produce folding and metastable kinetically limited states. This 1/4 exponent is a surprising agreement with the well-known value of 1/4 for coarsening dynamics in viscoelastic media. We try to establish a link between these two processes, hitherto considered unrelated, and with superdomains and domain bundles. We note also that high-Tc superconductors share many of the ferroelastic domain properties discussed here and that several new solar cell materials and metalinsulator transition systems are ferroelastic
Superdomain dynamics in ferroelectric-ferroelastic films: Switching, jamming, and relaxation
Recent experimental work shows that ferroelectric switching can occur in large jumps in which ferroelastic superdomains switch together, rather than having the numerous smaller ferroelectric domains switch within them. In this sense, the superdomains play a role analogous to that of Abrikosov vortices in thin superconducting films under the Kosterlitz-Thouless framework, which control the dynamics more than individual Cooper pairs within them do. Here, we examine the dynamics of ferroelastic superdomains in ferroelastic ferroelectrics and their role in switching devices such as memories. Jamming of ferroelectric domains in thin films has revealed an unexpected time dependence of t-1/4 at long times (hours), but it is difficult to discriminate between power-law and exponential relaxation. Other aspects of this work, including spatial period doubling of domains, led to a description of ferroelastic domains as nonlinear processes in a viscoelastic medium, which produce folding and metastable kinetically limited states. This 1/4 exponent is a surprising agreement with the well-known value of 1/4 for coarsening dynamics in viscoelastic media. We try to establish a link between these two processes, hitherto considered unrelated, and with superdomains and domain bundles. We note also that high-Tc superconductors share many of the ferroelastic domain properties discussed here and that several new solar cell materials and metalinsulator transition systems are ferroelastic
Negative Domain Wall Contribution to the Resistivity of Microfabricated Fe Wires
The effect of domain walls on electron transport has been investigated in
microfabricated Fe wires (0.65 to 20 linewidths) with controlled stripe
domains. Magnetoresistance (MR) measurements as a function of domain wall
density, temperature and the angle of the applied field are used to determine
the low field MR contributions due to conventional sources in ferromagnetic
materials and that due to the erasure of domain walls. A negative domain wall
contribution to the resistivity is found. This result is discussed in light of
a recent theoretical study of the effect of domain walls on quantum transport.Comment: 7 pages, 4 postscript figures and 1 jpg image (Fig. 1
Oscillatory Energy Exchange Between Waves Coupled by a Dynamic Artificial Crystal
We describe a general mechanism of controllable energy exchange between waves
propagating in a dynamic artificial crystal. We show that if a spatial
periodicity is temporarily imposed on the transmission properties of a
wave-carrying medium whilst a wave is inside, this wave is coupled to a
secondary counter-propagating wave and energy oscillates between the two. The
oscillation frequency is determined by the width of the spectral band gap
created by the periodicity and the frequency difference between the coupled
waves. The effect is demonstrated with spin waves in a dynamic magnonic
crystal.Comment: 5 pages, 4 figure
Manipulating Ferroelectric Domains in Nanostructures Under Electron Beams
Freestanding BaTiO3 nanodots exhibit domain structures characterized by
distinct quadrants of ferroelastic 90{\deg} domains in transmission electron
microscopy (TEM) observations. These differ significantly from flux-closure
domain patterns in the same systems imaged by piezoresponse force microscopy.
Based upon a series of phase field simulations of BaTiO3 nanodots, we suggest
that the TEM patterns result from a radial electric field arising from electron
beam charging of the nanodot. For sufficiently large charging, this converts
flux-closure domain patterns to quadrant patterns with radial net
polarizations. Not only does this explain the puzzling patterns that have been
observed in TEM studies of ferroelectric nanodots, but also suggests how to
manipulate ferroelectric domain patterns via electron beams.Comment: 5 pages, 6 figure
The ALHAMBRA photometric system
This paper presents the characterization of the optical range of the ALHAMBRA
photometric system, a 20 contiguous, equal-width, medium-band CCD system with
wavelength coverage from 3500A to 9700A. The photometric description of the
system is done by presenting the full response curve as a product of the
filters, CCD and atmospheric transmission curves, and using some first and
second order moments of this response function. We also introduce the set of
standard stars that defines the system, formed by 31 classic spectrophotometric
standard stars which have been used in the calibration of other known
photometric systems, and 288 stars, flux calibrated homogeneously, from the
Next Generation Spectral Library (NGSL). Based on the NGSL, we determine the
transformation equations between Sloan Digital Sky Survey (SDSS) ugriz
photometry and the ALHAMBRA photometric system, in order to establish some
relations between both systems. Finally we develop and discuss a strategy to
calculate the photometric zero points of the different pointings in the
ALHAMBRA project.Comment: Astronomical Journal on the 14th of January 201
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