182 research outputs found
Epitaxial thin films of multiferroic Bi2FeCrO6 with B-site cationic order
Epitaxial thin films of Bi2FeCrO6 have been synthesized by pulsed laser
deposition on SrRuO3 on (100)- and (111)-oriented SrTiO3 substrates. Detailed
X-ray diffraction and cross-section transmission electron microscopy analysis
revealed a double perovskite crystal structure of the Bi2FeCrO6 epitaxial films
very similar to that of BiFeO3 along with a particularly noteworthy Fe3+/Cr3+
cation ordering along the [111] direction. The films contain no detectable
magnetic iron oxide impurities and have the correct cationic average
stoichiometry throughout their thickness. They however exhibit a slight
modulation in the Fe and Cr compositions forming complementary stripe patterns,
suggesting minor local excess or depletion of Fe and Cr. The epitaxial BFCO
films exhibit good ferroelectric and piezoelectric properties, in addition to
magnetic properties at room temperature, as well as an unexpected
crystallographic orientation dependence of their room temperature magnetic
properties. Our results qualitatively confirm the predictions made using the
ab-initio calculations: the double-perovskite structure of Bi2FeCrO6 films
exhibit a Fe3+/Cr3+ cation ordering and good multiferroic properties, along
with the unpredicted existence of magnetic ordering at room temperature.Comment: Accepted for publication in Journal of Materials Researc
Polarization proximity effect in isolator crystal pairs
We experimentally studied the polarization dynamics (orientation and
ellipticity) of near infrared light transmitted through magnetooptic Yttrium
Iron Garnet crystal pairs using a modified balanced detection scheme. When the
pair separation is in the sub-millimeter range, we observed a proximity effect
in which the saturation field is reduced by up to 20%. 1D magnetostatic
calculations suggest that the proximity effect originates from magnetostatic
interactions between the dipole moments of the isolator crystals. This
substantial reduction of the saturation field is potentially useful for the
realization of low-power integrated magneto-optical devices.Comment: submitted to Optics Letter
Growth, Structure and Properties of BiFeO3-BiCrO3 Films obtained by Dual Cross Beam PLD
The properties of epitaxial Bi2FeCrO6 thin films, recently synthesized by
pulsed laser deposition, have partially confirmed the theoretical predictions
(i.e. a magnetic moment of 2 muB per formula unit and a polarization of ~80
microC/cm2 at 0K). The existence of magnetic ordering at room temperature for
this material is an unexpected but very promising result that needs to be
further investigated. Since magnetism is assumed to arise from the exchange
interaction between the Fe and Cr cations, the magnetic behaviour is strongly
dependent on both their ordering and the distance between them. We present here
the successful synthesis of epitaxial Bi2FexCryO6 (BFCO x/y) films grown on
SrTiO3 substrates using dual crossed beam pulsed laser deposition. The crystal
structure of the films has different types of (111)-oriented superstructures
depending on the deposition conditions. The multiferroic character of BFCO
(x/y) films is proven by the presence of both ferroelectric and magnetic
hysteresis at room temperature. The oxidation state of Fe and Cr ions in the
films is shown to be 3+ only and the difference in macroscopic magnetization
with Fe/Cr ratio composition could only be due to ordering of the Cr3+ and Fe3+
cations therefore to the modification of the exchange interaction between them.Comment: Manuscript accepted for publication in IEEE-UFF
Switching properties of self-assembled ferroelectric memory cells
In this letter, we report on the switching properties of an ordered system of Bi4Ti3O12 ferroelectric memory cells of an average lateral size of 0.18 μm formed via a self-assembling process. The ferroelectricity of these cells has been measured microscopically and it has been demonstrated that an individual cell of 0.18 μm size is switching. Switching of single nanoelectrode cells was achieved via scanning force microscopy working in piezoresponse mode
A Match in Time Saves Nine: Deterministic Online Matching With Delays
We consider the problem of online Min-cost Perfect Matching with Delays
(MPMD) introduced by Emek et al. (STOC 2016). In this problem, an even number
of requests appear in a metric space at different times and the goal of an
online algorithm is to match them in pairs. In contrast to traditional online
matching problems, in MPMD all requests appear online and an algorithm can
match any pair of requests, but such decision may be delayed (e.g., to find a
better match). The cost is the sum of matching distances and the introduced
delays.
We present the first deterministic online algorithm for this problem. Its
competitive ratio is , where is the
number of requests. This is polynomial in the number of metric space points if
all requests are given at different points. In particular, the bound does not
depend on other parameters of the metric, such as its aspect ratio. Unlike
previous (randomized) solutions for the MPMD problem, our algorithm does not
need to know the metric space in advance
Infrared and magnetic characterization of the multiferroic Bi2FeCrO6 thin films in a broad temperature range
Infrared reflectance spectra of an epitaxial Bi2FeCrO6 thin film prepared by
pulsed laser deposition on LaAlO3 substrate were recorded between 10 and 900 K.
No evidence for a phase transition to the paraelectric phase was observed, but
some phonon anomalies were revealed near 600 K. Most of the polar modes exhibit
only a gradual softening, which results in a continuous increase of the static
permittivity on heating. It indicates that the ferroelectric phase transition
should occur somewhere above 900 K. Magnetic measurements performed up to 1000
K, revealed a possible magnetic phase transition between 600 and 800 K, but the
exact critical temperature cannot be determined due to a strong diamagnetic
signal from the substrate. Nevertheless, our experimental data show that the
B-site ordered Bi2FeCrO6 is one of the rare high-temperature multiferroics.Comment: subm. to PR
Complex oxide nanostructures by pulsed laser deposition through nanostencils
We achieved parallel nanoscale patterning of ferroelectric complex oxides by pulsed laser deposition through a nanostencil (i.e., through a pattern of apertures in a thin free-standing membrane). Ordered arrays of nanostructured barium titanate (BaTiO3) were obtained onto different substrates in a single deposition step, at room temperature, replicating accurately the aperture patterns in the stencil membrane. After a postdeposition annealing treatment, x-ray diffraction pattern showed a nanocrystalline BaTiO3 structure close to the perovskite cubic phase with grains 30-35 nm in size. Their local ferroelectric properties were detected using piezoresponse force microscopy
Epitaxially stabilized thin films of ɛ-Fe₂O₃ (001) grown on YSZ (100)
Epsilon ferrite (epsilon-Fe2O3) is a metastable phase of iron(III) oxide, intermediate between maghemite and hematite. It has recently attracted interest because of its magnetocrystalline anisotropy, which distinguishes it from the other polymorphs, and results in a gigantic coercive field and a natural ferromagnetic resonance frequency in the THz range. Moreover, it possesses a polar crystal structure, making it a potential ferroelectric, hence a potential multiferroic. Due to the need of size confinement to stabilize the metastable phase, epsilon-Fe2O3 has been synthesized mainly as nanoparticles. However, to favor integration in devices, and take advantage of its unique functional properties, synthesis as epitaxial thin films is desirable. In this paper, we report the growth of epsilon-Fe2O3 as epitaxial thin films on (100)-oriented yttrium-stabilized zirconia substrates. Structural characterization outlined the formation of multiple in-plane twins, with two different epitaxial relations to the substrate. Transmission electron microscopy showed how such twins develop in a pillar-like structure from the interface to the surface. Magnetic characterization confirmed the high magnetocrystalline anisotropy of our film and revealed the presence of a secondary phase which was identified as the well-known magnetite. Finally, angular analysis of the magnetic properties revealed how the presence of twins impacts their azimuthal dependence
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