940 research outputs found
Magnetic frustration in an iron based Cairo pentagonal lattice
The Fe3+ lattice in the Bi2Fe4O9 compound is found to materialize the first
analogue of a magnetic pentagonal lattice. Due to its odd number of bonds per
elemental brick, this lattice, subject to first neighbor antiferromagnetic
interactions, is prone to geometric frustration. The Bi2Fe4O9 magnetic
properties have been investigated by macroscopic magnetic measurements and
neutron diffraction. The observed non-collinear magnetic arrangement is related
to the one stabilized on a perfect tiling as obtained from a mean field
analysis with direct space magnetic configurations calculations. The
peculiarity of this structure arises from the complex connectivity of the
pentagonal lattice, a novel feature compared to the well-known case of
triangle-based lattices
Anisotropic interactions opposing magnetocrystalline anisotropy in SrNiIrO
We report our investigation of the electronic and magnetic excitations of
SrNiIrO by resonant inelastic x-ray scattering at the Ir L edge.
The intra- electronic transitions are analyzed using an atomic model,
including spin-orbit coupling and trigonal distortion of the IrO
octahedron, confronted to {\it ab initio} quantum chemistry calculations. The
Ir spin-orbital entanglement is quantified and its implication on the magnetic
properties, in particular in inducing highly anisotropic magnetic interactions,
is highlighted. These are included in the spin-wave model proposed to account
for the dispersionless magnetic excitation that we observe at 90 meV. By
counterbalancing the strong Ni easy-plane anisotropy that manifests
itself at high temperature, the anisotropy of the interactions finally leads to
the remarkable easy-axis magnetism reported in this material at low
temperature
Tunable gauge potential for neutral and spinless particles in driven lattices
We present a universal method to create a tunable, artificial vector gauge
potential for neutral particles trapped in an optical lattice. The necessary
Peierls phase of the hopping parameters between neighboring lattice sites is
generated by applying a suitable periodic inertial force such that the method
does not rely on any internal structure of the particles. We experimentally
demonstrate the realization of such artificial potentials, which generate
ground state superfluids at arbitrary non-zero quasi-momentum. We furthermore
investigate possible implementations of this scheme to create tuneable magnetic
fluxes, going towards model systems for strong-field physics
Inhomogeneous magnetism in the doped kagome lattice of LaCuO2.66
The hole-doped kagome lattice of Cu2+ ions in LaCuO2.66 was investigated by
nuclear quadrupole resonance (NQR), electron spin resonance (ESR), electrical
resistivity, bulk magnetization and specific heat measurements. For
temperatures above ~180 K, the spin and charge properties show an activated
behavior suggestive of a narrow-gap semiconductor. At lower temperatures, the
results indicate an insulating ground state which may or may not be charge
ordered. While the frustrated spins in remaining patches of the original kagome
lattice might not be directly detected here, the observation of coexisting
non-magnetic sites, free spins and frozen moments reveals an intrinsically
inhomogeneous magnetism. Numerical simulations of a 1/3-diluted kagome lattice
rationalize this magnetic state in terms of a heterogeneous distribution of
cluster sizes and morphologies near the site-percolation threshold
Crystal Symmetry Lowering in Chiral Multiferroic BaTaFeSiO observed by X-Ray Magnetic Scattering
Chiral multiferroic langasites have attracted attention due to their
doubly-chiral magnetic ground state within an enantiomorphic crystal. We report
on a detailed resonant soft X-ray diffraction study of the multiferroic
BaTaFeSiO at the Fe and oxygen edges. Below
() we observe the satellite reflections ,
, and where . The dependence of the scattering intensity on X-ray polarization and
azimuthal angle indicate that the odd harmonics are dominated by the
out-of-plane (-axis) magnetic dipole while the
originates from the electron density distortions accompanying magnetic order.
We observe dissimilar energy dependences of the diffraction intensity of the
purely magnetic odd-harmonic satellites at the Fe edge. Utilizing
first-principles calculations, we show that this is a consequence of the loss
of threefold crystal symmetry in the multiferroic phase
Describing ancient horizontal gene transfers at the nucleotide and gene levels by comparative pathogenicity island genometrics
Motivation: Lateral gene transfer is a major mechanism contributing to bacterial genome dynamics and pathovar emergence via pathogenicity island (PAI) spreading. However, since few of these genomic exchanges are experimentally reproducible, it is difficult to establish evolutionary scenarios for the successive PAI transmissions between bacterial genera. Methods initially developed at the gene and/or nucleotide level for genomics, i.e. comparisons of concatenated sequences, ortholog frequency, gene order or dinucleotide usage, were combined and applied here to homologous PAIs: we call this approach comparative PAI genometrics. Results: YAPI, a Yersinia PAI, and related islands were compared with measure evolutionary relationships between related modules. Through use of our genometric approach designed for tracking codon usage adaptation and gene phylogeny, an ancient inter-genus PAI transfer was oriented for the first time by characterizing the genomic environment in which the ancestral island emerged and its subsequent transfers to other bacterial genera. Contact: [email protected] Supplementary informatio
Magnetic properties of the honeycomb oxide NaCoTeO
We have studied the magnetic properties of NaCoTeO, which
features a honeycomb lattice of magnetic Co ions, through macroscopic
characterization and neutron diffraction on a powder sample. We have shown that
this material orders in a zig-zag antiferromagnetic structure. In addition to
allowing a linear magnetoelectric coupling, this magnetic arrangement displays
very peculiar spatial magnetic correlations, larger in the honeycomb planes
than between the planes, which do not evolve with the temperature. We have
investigated this behavior by Monte Carlo calculations using the
-- model on a honeycomb lattice with a small interplane
interaction. Our model reproduces the experimental neutron structure factor,
although its absence of temperature evolution must be due to additional
ingredients, such as chemical disorder or quantum fluctuations enhanced by the
proximity to a phase boundary.Comment: 9 pages, 13 figure
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