170 research outputs found
Electrical switching of magnetic polarity in a multiferroic BiFeO3 device at room temperature
We have directly imaged reversible electrical switching of the cycloidal
rotation direction (magnetic polarity) in a (111)-BiFeO3 epitaxial-film device
at room temperature by non-resonant x-ray magnetic scattering. Consistent with
previous reports, fully relaxed (111)-BiFeO3 epitaxial films consisting of a
single ferroelectric domain were found to comprise a sub-micron-scale mosaic of
magneto-elastic domains, all sharing a common direction of the magnetic
polarity, which was found to switch reversibly upon reversal of the
ferroelectric polarization without any measurable change of the magneto-elastic
domain population. A real-space polarimetry map of our device clearly
distinguished between regions of the sample electrically addressed into the two
magnetic states with a resolution of a few tens of micron. Contrary to the
general belief that the magneto-electric coupling in BiFeO3 is weak, we find
that electrical switching has a dramatic effect on the magnetic structure, with
the magnetic moments rotating on average by 90 degrees at every cycle.Comment: 6 pages, 5 figures; corrected figure
Direct observation of charge order in triangular metallic AgNiO2 by single-crystal resonant X-ray scattering
We report resonant X-ray scattering measurements on the orbitally-degenerate
triangular metallic antiferromagnet 2H-AgNiO2 to probe the spontaneous
transition to a triple-cell superstructure at temperatures below 365 K. We
observe a strong resonant enhancement of the supercell reflections through the
Ni K-edge. The empirically extracted K-edge shift between the
crystallographically-distinct Ni sites of 2.5(3) eV is much larger than the
value expected from the shift in final states, and implies a core-level shift
of ~1 eV, thus providing direct evidence for the onset of spontaneous honeycomb
charge order in the triangular Ni layers. We also provide band-structure
calculations that explain quantitatively the observed edge shifts in terms of
changes in the Ni electronic energy levels due to charge order and
hybridization with the surrounding oxygens.Comment: 5 pages, 4 figure
Immunohistochemical Distribution of Serotonin Transporter (SERT) in the Optic Lobe of the Honeybee, Apis mellifera
Visual information is processed in the optic lobes, which consist of three retinotopic neuropils. These are the lamina, the medulla and the lobula. Biogenic amines play a crucial role in the control of insect responsiveness, and serotonin is clearly related to aggressiveness in invertebrates. Previous studies suggest that serotonin modulates aggression-related behaviours, possibly via alterations in optic lobe activity. The aim of this investigation was to immunohistochemically localize the distribution of serotonin transporter (SERT) in the optic lobe of moderate, docile and aggressive worker honeybees. SERT-immunoreactive fibres showed a wide distribution in the lamina, medulla and lobula; interestingly, the highest percentage of SERT immunoreactivity was observed across all the visual neuropils of the docile group. Although future research is needed to determine the relationship between the distribution of serotonin fibres in the honeybee brain and aggressive behaviours, our immunohistochemical study provides an anatomical basis supporting the role of serotonin in aggressive behaviour in the honeybee
Magnetically induced femtoscale strain modulations in HoMn2O5
International audienceX-ray scattering was used to investigate the magnetically induced ionic displacements in the low-temperature commensurate ferroelectric/antiferromagnetic phase of the multiferroic HoMn2O5. The structural modulation signal appearing at twice the magnetic wave vector km=(1/201/4) has been used, combined with symmetry analysis, to determine a model for the ionic displacements up to a precision of 10-3Ă…. The symmetry-breaking operations that are associated to the active irreducible representation have been experimentally determined from the analysis of the modulation modes. They reveal a lowering of symmetry to the polar point group m2m. Calculations based on the determined model show that the magnetic structure along the c direction is stabilized via nearest-neighbor and next-nearest-neighbor interactions through the rare-earth layer. We also show that by knowing both the magnetic and the magnetically induced strain waves patterns, it is possible to remove any phase ambiguity between the crystal and magnetic structures
Helical spin-waves, magnetic order, and fluctuations in the langasite compound Ba3NbFe3Si2O14
We have investigated the spin fluctuations in the langasite compound
Ba3NbFe3Si2O14 in both the ordered state and as a function of temperature. The
low temperature magnetic structure is defined by a spiral phase characterized
by magnetic Bragg peaks at q=(0,0,tau ~ 1/7) onset at TN=27 K as previously
reported by Marty et al. The nature of the fluctuations and temperature
dependence of the order parameter is consistent with a classical second order
phase transition for a two dimensional triangular antiferromagnet. We will show
that the physical properties and energy scales including the ordering
wavevector, Curie-Weiss temperature, and the spin-waves can be explained
through the use of only symmetric exchange constants without the need for the
Dzyaloshinskii-Moriya interaction. This is accomplished through a set of
``helical" exchange pathways along the c direction imposed by the chiral
crystal structure and naturally explains the magnetic diffuse scattering which
displays a strong vector chirality up to high temperatures well above the
ordering temperature. This illustrates a strong coupling between magnetic and
crystalline chirality in this compound.Comment: 16 pages, 16 figures, submitted to Physical Review
Non-coplanar and counter-rotating incommensurate magnetic order stabilized by Kitaev interactions in -Li2IrO3
Materials that realize Kitaev spin models with bond-dependent anisotropic
interactions have long been searched for, as the resulting frustration effects
are predicted to stabilize novel forms of magnetic order or quantum spin
liquids. Here we explore the magnetism of -LiIrO, which has the
topology of a 3D Kitaev lattice of inter-connected Ir honeycombs. Using
resonant magnetic x-ray diffraction we find a complex, yet highly-symmetric
incommensurate magnetic structure with non-coplanar and counter-rotating Ir
moments. We propose a minimal Kitaev-Heisenberg Hamiltonian that naturally
accounts for all key features of the observed magnetic structure. Our results
provide strong evidence that -LiIrO realizes a spin Hamiltonian
with dominant Kitaev interactions.Comment: 10 pages, 7 figure
Emergence of robust 2D skyrmions in SrRuO3 ultrathin film without the capping layer
Magnetic skyrmions have fast evolved from a novelty, as a realization of
topologically protected structure with particle-like character, into a
promising platform for new types of magnetic storage. Significant engineering
progress was achieved with the synthesis of compounds hosting room-temperature
skyrmions in magnetic heterostructures, with the interfacial
Dzyaloshinskii-Moriya interactions (DMI) conducive to the skyrmion formation.
Here we report findings of ultrathin skyrmion formation in a few layers of
SrRuO3 grown on SrTiO3 substrate without the heavy-metal capping layer.
Measurement of the topological Hall effect (THE) reveals a robust stability of
skyrmions in this platform, judging from the high value of the critical field
1.57 Tesla (T) at low temperature. THE survives as the field is tilted by as
much as 85 degrees at 10 Kelvin, with the in-plane magnetic field reaching up
to 6.5 T. Coherent Bragg Rod Analysis, or COBRA for short, on the same film
proves the rumpling of the Ru-O plane to be the source of inversion symmetry
breaking and DMI. First-principles calculations based on the structure obtained
from COBRA find significant magnetic anisotropy in the SrRuO3 film to be the
main source of skyrmion robustness. These features promise a few-layer SRO to
be an important new platform for skyrmionics, without the necessity of
introducing the capping layer to boost the spin-orbit coupling strength
artificially.Comment: Supplementary Information available upon reques
Emergence of robust 2D skyrmions in SrRuO3 ultrathin film without the capping layer
Magnetic skyrmions have fast evolved from a novelty, as a realization of
topologically protected structure with particle-like character, into a
promising platform for new types of magnetic storage. Significant engineering
progress was achieved with the synthesis of compounds hosting room-temperature
skyrmions in magnetic heterostructures, with the interfacial
Dzyaloshinskii-Moriya interactions (DMI) conducive to the skyrmion formation.
Here we report findings of ultrathin skyrmion formation in a few layers of
SrRuO3 grown on SrTiO3 substrate without the heavy-metal capping layer.
Measurement of the topological Hall effect (THE) reveals a robust stability of
skyrmions in this platform, judging from the high value of the critical field
1.57 Tesla (T) at low temperature. THE survives as the field is tilted by as
much as 85 degrees at 10 Kelvin, with the in-plane magnetic field reaching up
to 6.5 T. Coherent Bragg Rod Analysis, or COBRA for short, on the same film
proves the rumpling of the Ru-O plane to be the source of inversion symmetry
breaking and DMI. First-principles calculations based on the structure obtained
from COBRA find significant magnetic anisotropy in the SrRuO3 film to be the
main source of skyrmion robustness. These features promise a few-layer SRO to
be an important new platform for skyrmionics, without the necessity of
introducing the capping layer to boost the spin-orbit coupling strength
artificially.Comment: Supplementary Information available upon reques
Interplay of inequivalent atomic positions in resonant x-ray diffraction of Fe3BO6
'Forbidden' Bragg reflections of iron orthoborate Fe3BO6 were studied
theoretically and experimentally in the vicinity of the iron K edge. Their
energy spectra are explained as resulting from the interference of x-rays
scattered from two inequivalent crystallographic sites occupied by iron ions.
This particular structure property gives rise to complex azimuthal dependences
of the reflection intensities in the pre-edge region as they result from the
interplay of site specific dipole-quadrupole and quadrupole-quadrupole resonant
scattering. Also evidenced is an isotropic character of the absorption
spectrum. Self-absorption correction to the diffraction data, as well as
possible contributions of thermal vibrations and magnetic order, are discussed.
Particular care is given to extracting clean spectra from the data, and it is
demonstrated that excellent results can be obtained even from measurements that
appear corrupted by several effects such as poor crystal quality and multiple
scattering.Comment: 12 page
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