1,005 research outputs found
XY checkerboard antiferromagnet in external field
Ordering by thermal fluctuations is studied for the classical XY
antiferromagnet on a checkerboard lattice in zero and finite magnetic fields by
means of analytical and Monte Carlo methods. The model exhibits a variety of
novel broken symmetries including states with nematic ordering in zero field
and with triatic order parameter at high fields.Comment: 6 page
Observation of magnetic fragmentation in spin ice
Fractionalised excitations that emerge from a many body system have revealed
rich physics and concepts, from composite fermions in two-dimensional electron
systems, revealed through the fractional quantum Hall effect, to spinons in
antiferromagnetic chains and, more recently, fractionalisation of Dirac
electrons in graphene and magnetic monopoles in spin ice. Even more surprising
is the fragmentation of the degrees of freedom themselves, leading to
coexisting and a priori independent ground states. This puzzling phenomenon was
recently put forward in the context of spin ice, in which the magnetic moment
field can fragment, resulting in a dual ground state consisting of a
fluctuating spin liquid, a so-called Coulomb phase, on top of a magnetic
monopole crystal. Here we show, by means of neutron scattering measurements,
that such fragmentation occurs in the spin ice candidate NdZrO. We
observe the spectacular coexistence of an antiferromagnetic order induced by
the monopole crystallisation and a fluctuating state with ferromagnetic
correlations. Experimentally, this fragmentation manifests itself via the
superposition of magnetic Bragg peaks, characteristic of the ordered phase, and
a pinch point pattern, characteristic of the Coulomb phase. These results
highlight the relevance of the fragmentation concept to describe the physics of
systems that are simultaneously ordered and fluctuating.Comment: accepted in Nature Physic
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
Hierarchical geometric frustration in La3Cu2VO9
The crystallographic structure and magnetic properties of the La3Cu2VO9 were
investigated by powder neutron diffraction and magnetization measurements. The
compound materializes geometric frustration at two spatial scales, within
clusters and between clusters, and at different temperature scales. It is shown
by exactly solving the hamiltonian spectrum that collective spins are formed on
each clusters at low temperature before inter-clusters coupling operates.Comment: 6 pages, 4 figures. HFM2006 proceeding pape
Comparison of some behavioral and physiological feeding parameters of Triatoma infestans klug, 1834 and Mepraia spinolai porter, 1934, vectors of chagas disease in Chile
Artificial Kagome Arrays of Nanomagnets: A Frozen Dipolar Spin Ice
Magnetic frustration effects in artificial kagome arrays of nanomagnets are
investigated using x-ray photoemission electron microscopy and Monte Carlo
simulations. Spin configurations of demagnetized networks reveal unambiguous
signatures of long range, dipolar interaction between the nanomagnets. As soon
as the system enters the spin ice manifold, the kagome dipolar spin ice model
captures the observed physics, while the short range kagome spin ice model
fails.Comment: 4 pages, 4 figures, 1 tabl
Kondo Screening and Magnetic Ordering in Frustrated UNi4B
UNi4B exhibits unusual properties and, in particular, a unique
antiferromagnetic arrangement involving only 2/3 of the U sites. Based on the
low temperature behavior of this compound, we propose that the remaining 1/3 U
sites are nonmagnetic due to the Kondo effect. We derive a model in which the
coexistence of magnetic and nonmagnetic U sites is the consequence of the
competition between frustration of the crystallographic structure and
instability of the 5f moments.Comment: 4 pages, 2 figure
Exploring benthic biodiversity patterns and hotspots on European margin slopes
There is increasing evidence that continental slope ecosystems represent one of the major repositories of benthic marine biodiversity. The enhanced levels of biodiversity along slopes are hypothesized to be a source of biodiversity for continental shelves and deeper basins. Continental margins are increasingly altered by human activities, but the consequences of these anthropogenic impacts on benthic biodiversity and ecosystem functioning are almost completely unknown. Thus, there is an urgent need to gather sufficient information to enable us to understand patterns and drivers of deep sea biodiversity along continental margins. Although the local diversity of some deep open slope ecosystems is moderately well documented, very little is known about the biodiversity of these systems at greater spatial scales. Topographic setting, hydrodynamic forcing, and the biogeochemical characteristics of the deep-sea floor may play key roles in promoting and sustaining high biodiversity along the open slopes of continental margins. HERMES provided the opportunity to acquire a significant volume of information on the biodiversity, trophic conditions, and topographic characteristics of open slopes across European margins, increasing our knowledge of the latitudinal, longitudinal, and bathymetric patterns of benthic biodiversity, and extending our comprehension of the mechanisms driving deep-sea biodiversity and its potential loss. Improved knowledge of these processes is needed to inform policy decisions for promoting sustainable management of open slopes and deep-sea ecosystems along continental margins
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