4,530 research outputs found
Spin-stripe phase in a frustrated zigzag spin-1/2 chain
Motifs of periodic modulations are encountered in a variety of natural
systems, where at least two rival states are present. In strongly correlated
electron systems such behaviour has typically been associated with competition
between short- and long-range interactions, e.g., between exchange and
dipole-dipole interactions in the case of ferromagnetic thin films. Here we
show that spin-stripe textures may develop also in antiferromagnets, where
long-range dipole-dipole magnetic interactions are absent. A comprehensive
analysis of magnetic susceptibility, high-field magnetization, specific heat,
and neutron diffraction measurements unveils -TeVO as a nearly
perfect realization of a frustrated (zigzag) ferromagnetic spin-1/2 chain.
Strikingly, a narrow spin stripe phase develops at elevated magnetic fields due
to weak frustrated short-range interchain exchange interactions possibly
assisted by the symmetry allowed electric polarization. This concept provides
an alternative route for the stripe formation in strongly correlated electron
systems and may help understanding other widespread, yet still elusive,
stripe-related phenomena.Comment: accapted in Nature Communication
Non-collinear long-range magnetic ordering in HgCr2S4
The low-temperature magnetic structure of \HG has been studied by
high-resolution powder neutron diffraction. Long-range incommensurate magnetic
order sets in at T22K with propagation vector
\textbf{k}=(0,0,0.18). On cooling below T, the propagation vector
increases and saturates at the commensurate value \textbf{k}=(0,0,0.25). The
magnetic structure below T consists of ferromagnetic layers in the
\textit{ab}-plane stacked in a spiral arrangement along the \textit{c}-axis.
Symmetry analysis using corepresentations theory reveals a point group symmetry
in the ordered magnetic phase of 422 (D), which is incompatible with
macroscopic ferroelectricity. This finding indicates that the spontaneous
electric polarization observed experimentally cannot be coupled to the magnetic
order parameter
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
The Potential for Summer-Dormant Perennial Grasses in Mediterranean and Semi-Arid Pastures
In rain-fed Mediterranean and semi-arid areas, herbage production of perennial grasses depends on their ability to grow efficiently during the rainy seasons and to persist over the dry summer. A key survival strategy in these harsh conditions is summer dormancy (Volaire, 2002). Within the species Dactylis glomerata L., two cultivars (cvs.), contrasting in this trait, were compared in order to analyse their suitability in terms of yield and survival in these environments
Magneto and ferroelectric phase transitions in HoMn2O5 monocrystals
From the physical point of view multiferroics present an extremely
interesting class of systems and problems. These are essentially of two kinds.
One is what are the microscopic conditions, and sometimes constrains, which
determine the possibility to combine in one system both magnetic and
ferroelectric properties. This turned out to be a quite nontrivial question,
and usually, in conventional systems, these two phenomena tend to exclude one
another. Why it is the case is an important and still not completely resolved
issue. In the present article we report our results from magnetic properties
measurements on HoMn2O5 with short discussion about it possible origin
Trisomy 19 ependymoma, a newly recognized genetico-histological association, including clear cell ependymoma
Ependymal tumors constitute a clinicopathologically heterogeneous group of brain tumors. They vary in regard to their age at first symptom, localization, morphology and prognosis. Genetic data also suggests heterogeneity. We define a newly recognized subset of ependymal tumors, the trisomy 19 ependymoma. Histologically, they are compact lesions characterized by a rich branched capillary network amongst which tumoral cells are regularly distributed. When containing clear cells they are called clear cell ependymoma. Most trisomy 19 ependymomas are supratentorial WHO grade III tumors of the young. Genetically, they are associated with trisomy 19, and frequently with a deletion of 13q21.31-31.2, three copies of 11q13.3-13.4, and/or deletions on chromosome 9. These altered chromosomal regions are indicative of genes and pathways involved in trisomy 19 ependymoma tumorigenesis. Recognition of this genetico-histological entity allows better understanding and dissection of ependymal tumors
Prediction for new magnetoelectric fluorides
We use symmetry considerations in order to predict new magnetoelectric
fluorides. In addition to these magnetoelectric properties, we discuss among
these fluorides the ones susceptible to present multiferroic properties. We
emphasize that several materials present ferromagnetic properties. This
ferromagnetism should enhance the interplay between magnetic and dielectric
properties in these materials.Comment: 12 pages, 4 figures, To appear in Journal of Physics: Condensed
Matte
Vieillissement et territoires: cadres théoriques et enjeux empiriques
The goal of this paper is to present the interest of the concept of territory in the apprehension of gerontological dynamics, especially by showing how a systemic approach proves territory propitious in the analysis and understanding production processes, organization, inclusion and exclusion in the gerontological field
One-dimensional magnetic fluctuations in the spin-2 triangular lattice \alpha-NaMnO2
The S=2 anisotropic triangular lattice alpha-NaMnO2 is studied by neutron
inelastic scattering. Antiferromagnetic order occurs at T ~ 45 K with opening
of a spin gap. The spectral weight of the magnetic dynamics above the gap
(Delta ~ 7.5 meV) has been analysed by the single-mode approximation. Excellent
agreement with the experiment is achieved when a dominant exchange interaction
(|J|/k_B ~ 73 K), along the monoclinic b-axis and a sizeable easy-axis magnetic
anisotropy (|D|/k_B ~ 3 K) are considered. Despite earlier suggestions for
two-dimensional spin interactions, the dynamics illustrate strongly coupled
antiferromagnetic S=2 chains and cancellation of the interchain exchange due to
the lattice topology. alpha-NaMnO2 therefore represents a model system where
the geometric frustration is resolved through the lowering of the
dimensionality of the spin interactions.Comment: 4 pages, 4 figures, to be published in Physical Review Letter
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