1,687 research outputs found
Fractal dimension and size scaling of domains in thin films of multiferroic BiFeO3
We have analyzed the morphology of ferroelectric domains in very thin films
of multiferroic BiFeO3. Unlike the more common stripe domains observed in
thicker films BiFeO3 or in other ferroics, the domains tend not to be straight,
but irregular in shape, with significant domain wall roughening leading to a
fractal dimensionality. Also contrary to what is usually observed in other
ferroics, the domain size appears not to scale as the square root of the film
thickness. A model is proposed in which the observed domain size as a function
of film thickness can be directly linked to the fractal dimension of the
domains.Comment: 4 pages, 3 figure
Topology of the polarization field in ferroelectric nanowires from first principles
The behaviour of the cross-sectional polarization field is explored for thin
nanowires of barium titanate from first-principles calculations. Topological
defects of different winding numbers have been obtained, beyond the known
textures in ferroelectric nanostructures. They result from the inward
accommodation of the polarization patterns imposed at the surface of the wire
by surface and edge effects. Close to a topological defect the polarization
field orients out of the basal plane in some cases, maintaining a close to
constant magnitude, whereas it virtually vanishes in other cases.Comment: 4 pages, 3 figure
Effect of manganese doping on the size effect of lead zirconate titanate thin films and the extrinsic nature of dead layers
We have investigated the size effect in lead zirconate titanate (PZT) thin
films with a range of manganese (Mn) doping concentrations. We found that the
size effect in the conventional Pt/PZT/Pt thin-film capacitors could be
systematically reduced and almost completely eliminated by increasing Mn doping
concentration. The interfacial layer at the electrode-film interface appears to
disappear almost entirely for the PZT films with 2% Mn doping levels, confirmed
by the fits using the conventional in-series capacitor model. Our work
indicates that the size effect in ferroelectrics is extrinsic in nature,
supporting the work by Saad et al. Other implications of our results have also
been discussed. By comparing a variety of experimental studies in the
literature we propose a scenario that the dead layer between PZT (or barium
strontium titanate, BST) and metal electrodes such as Pt and Au might have a
defective pyrochlore/fluorite structure (possibly with a small portion of
ferroelectric perovskite phase).Comment: 21 pages, 6 figure
A Collimation Experiment with Protons at 120 GeV
We present the preliminary results of a two-stage collimation experiment made with a 120 GeV coasting proton beam in the SPS at CERN
Landau Theory of Domain Wall Magnetoelectricity
We calculate the exact analytical solution to the domain wall properties in a
multiferroic system with two order parameters that are coupled
bi-quadratically. This is then adapted to the case of a magnetoelectric
multiferroic material such as BiFeO3, with a view to examine critically whether
the domain walls can account for the enhancement of magnetization reported for
thin films fo this material, in view of the correlation between increasing
magnetization and increasing volume fraction of domain walls as films become
thinner. The present analysis can be generalized to describe a class of
magnetoelectric devices based upon domain walls rather than bulk properties.Comment: 9 pages, 4 figure
Strain Gradients in Epitaxial Ferroelectrics
X-ray analysis of ferroelectric thin layers of Ba1/2Sr1/2TiO3 with different
thickness reveals the presence of internal strain gradients across the film
thickness and allows us to propose a functional form for the internal strain
profile. We use this to calculate the direct influence of strain gradient,
through flexoelectric coupling, on the degradation of the ferroelectric
properties of thin films with decreasing thickness, in excellent agreement with
the observed behaviour. This work highlights the link between strain relaxation
and strain gradients in epitaxial films, and shows the pressing need to avoid
strain gradients in order to obtain thin ferroelectrics with bulk-like
properties.Comment: 4 pages, 3 embedded figures (1 color), revTex
The Catalina Real-time Transient Survey
The Catalina Real-time Transient Survey (CRTS) currently covers 33,000 deg^2
of the sky in search of transient astrophysical events, with time baselines
ranging from 10 minutes to ~7 years. Data provided by the Catalina Sky Survey
provides an unequaled baseline against which >4,000 unique optical transient
events have been discovered and openly published in real-time. Here we
highlight some of the discoveries of CRTS.Comment: To appear in proc. IAU Symp. 285, "New Horizons in Time Domain
Astronomy", eds. E. Griffin et al., Cambridge Univ. Press (2012), 3 page
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