121 research outputs found
Very large spontaneous electric polarization in BiFeO3 single crystals at room temperature and its evolution under cycling fields
Electric polarization loops are measured at room temperature on highly pure
BiFeO3 single crystals synthesized by a flux growth method. Because the
crystals have a high electrical resistivity, the resulting low leakage currents
allow us to measure a large spontaneous polarization reaching 100
microC.cm^{-2}, a value never reported in the bulk. During electric cycling,
the slow degradation of the material leads to an evolution of the hysteresis
curves eventually preventing full saturation of the crystals.Comment: 8 pages, 3 figure
Infrared phonon dynamics of multiferroic BiFeO3 single crystal
We discuss the first infrared reflectivity measurement on a BiFeO3 single
crystal between 5 K and room temperature. The 9 predicted ab-plane E phonon
modes are fully and unambiguously determined. The frequencies of the 4 A1
c-axis phonons are found. These results settle issues between theory and data
on ceramics. Our findings show that the softening of the lowest frequency E
mode is responsible for the temperature dependence of the dielectric constant,
indicating that the ferroelectric transition in BiFeO3 is soft-mode driven.Comment: 5 pages (figures included
Electric-field control of spin waves at room temperature in multiferroic BiFeO3
To face the challenges lying beyond current CMOS-based technology, new
paradigms for information processing are required. Magnonics proposes to use
spin waves to carry and process information, in analogy with photonics that
relies on light waves, with several advantageous features such as potential
operation in the THz range and excellent coupling to spintronics. Several
magnonic analog and digital logic devices have been proposed, and some
demonstrated. Just as for spintronics, a key issue for magnonics is the large
power required to control/write information (conventionally achieved through
magnetic fields applied by strip lines, or by spin transfer from large
spin-polarized currents). Here we show that in BiFeO3, a room-temperature
magnetoelectric material, the spin wave frequency (>600 GHz) can be tuned
electrically by over 30%, in a non-volatile way and with virtually no power
dissipation. Theoretical calculations indicate that this effect originates from
a linear magnetoelectric effect related to spin-orbit coupling induced by the
applied electric field. We argue that these properties make BiFeO3 a promising
medium for spin wave generation, conversion and control in future magnonics
architectures.Comment: 3 figure
Polar phonons and spin excitations coupling in multiferroic BiFeO3 crystals
Raman scattering measurements on BiFeO3 single crystals show an important
coupling between the magnetic order and lattice vibrations. The temperature
evolution of phonons shows that the lowest energy E and A1 phonon modes are
coupled to the spin order up to the Neel temperature. Furthermore, low
temperature anomalies associated with the spin re-orientation are observed
simultaneously in both the E phonon and the magnon. These results suggest that
magnetostriction plays an important role in BiFeO3
Electric-field-induced spin-flop in BiFeO3 single crystals at room-temperature
Bismuth ferrite, BiFeO3, is the only known room-temperature 'multiferroic'
material. We demonstrate here, using neutron scattering measurements in high
quality single crystals, that the antiferromagnetic and ferroelectric orders
are intimately coupled. Initially in a single ferroelectric state, our crystals
have a canted antiferromagnetic structure describing a unique cycloid. Under
electrical poling, polarisation re-orientation induces a spin flop. We argue
here that the coupling between the two orders may be stronger in the bulk than
that observed in thin films where the cycloid is absent
Room temperature coexistence of large electric polarization and magnetic order in BiFeO3 single crystals
From an experimental point of view, room temperature ferroelectricity in
BiFeO3 is raising many questions. Electric measurements made a long time ago on
solid-solutions of BiFeO3 with Pb(Ti,Zr)O3 indicate that a spontaneous electric
polarization exists in BiFeO3 below the Curie temperature TC=1143K. Yet in most
reported works, the synthesised samples are too conductive at room temperature
to get a clear polarization loop in the bulk without any effects of extrinsic
physical or chemical parameters. Surprisingly, up to now there has been no
report of a P(E) (polarization versus electric field) loop at room temperature
on single crystals of BiFeO3. We describe here our procedure to synthesize
ceramics and to grow good quality sizeable single crystals by a flux method. We
demonstrate that BiFeO3 is indeed ferroelectric at room-temperature through
evidence by Piezoresponse Force Microscopy and P(E) loops. The polarization is
found to be large, around 60 microC/cm2, a value that has only been reached in
thin films. Magnetic measurements using a SQUID magnetometer and Mossbauer
spectroscopy are also presented. The latter confirms the results of NMR
measurements concerning the anisotropy of the hyperfine field attributed to the
magnetic cycloidal structure.Comment: 27 pages, 12 figure
Influence of parasitic phases on the properties of BiFeO3 epitaxial thin films
We have explored the influence of deposition pressure and temperature on the
growth of BiFeO3 thin films by pulsed laser deposition onto (001)-oriented
SrTiO3 substrates. Single-phase BiFeO3 films are obtained in a region close to
10-2 mbar and 580C. In non-optimal conditions, X-ray diffraction reveals the
presence of Fe oxides or of Bi2O3. We address the influence of these parasitic
phases on the magnetic and electrical properties of the films and show that
films with Fe2O3 systematically exhibit a ferromagnetic behaviour, while
single-phase films have a low bulk-like magnetic moment. Conductive-tip atomic
force microscopy mappings also indicate that Bi2O3 conductive outgrowths create
shortcuts through the BiFeO3 films, thus preventing their practical use as
ferroelectric elements in functional heterostructures.Comment: sumbitted to Appl. Phys. Let
Simple top-down preparation of magnetic BiGdFeTiO nanoparticles by ultrasonication of multiferroic bulk material
We present a simple technique to synthesize ultrafine nanoparticles directly
from bulk multiferroic perovskite powder. The starting materials, which were
ceramic pellets of the nominal compositions of
BiGdFeTiO (x = 0.00-0.20), were prepared
initially by a solid state reaction technique, then ground into
micrometer-sized powders and mixed with isopropanol or water in an ultrasonic
bath. The particle size was studied as a function of sonication time with
transmission electron microscopic imaging and electron diffraction that
confirmed the formation of a large fraction of single-crystalline nanoparticles
with a mean size of 11-13 nm. A significant improvement in the magnetic
behavior of BiGdFeTiO nanoparticles compared to
their bulk counterparts was observed at room temperature. This sonication
technique may be considered as a simple and promising route to prepare
ultrafine nanoparticles for functional applications.Comment: 7 pages, 5 figure
Concurrent transition of ferroelectric and magnetic ordering near room temperature
Strong spin-lattice coupling in condensed matter gives rise to intriguing physical phenomena such as colossal magnetoresistance and giant magnetoelectric effects. The phenomenological hallmark of such a strong spin-lattice coupling is the manifestation of a large anomaly in the crystal structure at the magnetic transition temperature. Here we report that the magnetic Néel temperature of the multiferroic compound BiFeO3 is suppressed to around room temperature by heteroepitaxial misfit strain. Remarkably, the ferroelectric state undergoes a first-order transition to another ferroelectric state simultaneously with the magnetic transition temperature. Our findings provide a unique example of a concurrent magnetic and ferroelectric transition at the same temperature among proper ferroelectrics, taking a step toward room temperature magnetoelectric applications. © 2011 Macmillan Publishers Limited. All rights reserved.open435
- …