80 research outputs found
Gradual Enhancement of Stripe-Type Antiferromagnetism in Spin Ladder Material BaFeS Under Pressure
We report pressure-dependent neutron diffraction and muon spin
relaxation/rotation measurements combined with first-principles calculations to
investigate the structural, magnetic, and electronic properties of
BaFeS under pressure. The experimental results reveal a gradual
enhancement of the stripe-type ordering temperature with increasing pressure up
to 2.6 GPa and no observable change in the size of the ordered moment. The ab
initio calculations suggest that the magnetism is highly sensitive to the Fe-S
bond lengths and angles, clarifying discrepancies with previously published
results. In contrast to our experimental observations, the calculations predict
a monotonic reduction of the ordered moment with pressure. We suggest that the
robustness of the stripe-type antiferromagnetism is due to strong electron
correlations not fully considered in the calculations
Extended Magnetic Dome Induced by Low Pressures in Superconducting FeSeS
We report muon spin rotation (SR) and magnetization measurements under
pressure on FeSeS with x
.Above GPa we find microscopic coexistence of
superconductivity with an extended dome of long range magnetic order that spans
a pressure range between previously reported separated magnetic phases. The
magnetism initially competes on an atomic scale with the coexisting
superconductivity leading to a local maximum and minimum of the superconducting
. The maximum of corresponds to the onset of
magnetism while the minimum coincides with the pressure of strongest
competition. A shift of the maximum of for a series of single
crystals with x up to 0.14 roughly extrapolates to a putative magnetic and
superconducting state at ambient pressure for x .Comment: 10 pages, 6 figures, including supplemental materia
Universal fluctuating regime in triangular chromate antiferromagnets
We report x-ray diffraction, magnetic susceptibility, heat capacity, H
nuclear magnetic resonance (NMR), and muon spin relaxation (SR)
measurements, as well as density-functional band-structure calculations for the
frustrated triangular lattice Heisenberg antiferromagnet (TLHAF)
-HCrO (trigonal, space group: ). This compound
undergoes a clear magnetic transition at ~K, as seen
from the drop in the muon paramagnetic fraction and concurrent anomalies in the
magnetic susceptibility and specific heat. Local probes (NMR and SR)
reveal a broad regime with slow fluctuations down to , this
temperature corresponding to the maximum in the SR relaxation rate and in
the NMR wipe-out. From the comparison with NaCrO and -KCrO,
the fluctuating regime and slow dynamics below appear to be
hallmarks of the TLHAF with stacking that leads to a frustration of
interlayer couplings between the triangular planes. This interlayer frustration
is a powerful lever to generate spin states with persistent dynamics and may
bear implications to spin-liquid candidates with the triangular geometry.Comment: 14 pages, 11 figures, 2 table
Disordered ground state in the spin-orbit coupled Jeff = 1/2 distorted honeycomb magnet BiYbGeO5
We delineate quantum magnetism in the strongly spin-orbit coupled distorted honeycomb lattice antiferromagnet BiYbGeO5. Our magnetization and heat capacity measurements reveal that its low-temperature behavior is well described by an effective Jeff=12 Kramers doublet of Yb3+. The ground state is nonmagnetic with a tiny spin gap. Temperature-dependent magnetic susceptibility, magnetization isotherm, and heat capacity can be modeled well assuming isolated spin dimers with anisotropic exchange interactions JZ≃2.6 K and JXY≃1.3 K. Heat capacity measurements backed by muon spin relaxation suggest the absence of magnetic long-range order down to at least 80 mK both in zero field and in applied fields. This sets BiYbGeO5 apart from Yb2Si2O7, with its unusual regime of magnon Bose-Einstein condensation, and suggests negligible interdimer couplings, despite only a weak structural deformation of the honeycomb lattice
Robust block magnetism in the spin ladder compound BaFeSe under hydrostatic pressure
The majority of the iron-based superconductors (FeSCs) exhibit a
two-dimensional square lattice structure. Recent reports of pressure-induced
superconductivity in the spin-ladder system, BaFeX (X =S,Se), introduce
a quasi-one-dimensional prototype and an insulating parent compound to the
FeSCs. Here we report X-ray, neutron diffraction and muon spin relaxation
experiments on BaFeSe under hydrostatic pressure to investigate its
magnetic and structural properties across the pressure-temperature phase
diagram. A structural phase transition was identified at a pressure of 3.7(3)
GPa. Neutron diffraction measurements at 6.8(3) GPa and 120 K show that the
block magnetism persists even at these high pressures. A steady increase and
then fast drop of the magnetic transition temperature and greatly
reduced moment above the pressure indicate potentially rich and competing
phases close to the superconducting phase in this ladder system
Antimicrobial resistance among migrants in Europe: a systematic review and meta-analysis
BACKGROUND: Rates of antimicrobial resistance (AMR) are rising globally and there is concern that increased migration is contributing to the burden of antibiotic resistance in Europe. However, the effect of migration on the burden of AMR in Europe has not yet been comprehensively examined. Therefore, we did a systematic review and meta-analysis to identify and synthesise data for AMR carriage or infection in migrants to Europe to examine differences in patterns of AMR across migrant groups and in different settings. METHODS: For this systematic review and meta-analysis, we searched MEDLINE, Embase, PubMed, and Scopus with no language restrictions from Jan 1, 2000, to Jan 18, 2017, for primary data from observational studies reporting antibacterial resistance in common bacterial pathogens among migrants to 21 European Union-15 and European Economic Area countries. To be eligible for inclusion, studies had to report data on carriage or infection with laboratory-confirmed antibiotic-resistant organisms in migrant populations. We extracted data from eligible studies and assessed quality using piloted, standardised forms. We did not examine drug resistance in tuberculosis and excluded articles solely reporting on this parameter. We also excluded articles in which migrant status was determined by ethnicity, country of birth of participants' parents, or was not defined, and articles in which data were not disaggregated by migrant status. Outcomes were carriage of or infection with antibiotic-resistant organisms. We used random-effects models to calculate the pooled prevalence of each outcome. The study protocol is registered with PROSPERO, number CRD42016043681. FINDINGS: We identified 2274 articles, of which 23 observational studies reporting on antibiotic resistance in 2319 migrants were included. The pooled prevalence of any AMR carriage or AMR infection in migrants was 25·4% (95% CI 19·1-31·8; I2 =98%), including meticillin-resistant Staphylococcus aureus (7·8%, 4·8-10·7; I2 =92%) and antibiotic-resistant Gram-negative bacteria (27·2%, 17·6-36·8; I2 =94%). The pooled prevalence of any AMR carriage or infection was higher in refugees and asylum seekers (33·0%, 18·3-47·6; I2 =98%) than in other migrant groups (6·6%, 1·8-11·3; I2 =92%). The pooled prevalence of antibiotic-resistant organisms was slightly higher in high-migrant community settings (33·1%, 11·1-55·1; I2 =96%) than in migrants in hospitals (24·3%, 16·1-32·6; I2 =98%). We did not find evidence of high rates of transmission of AMR from migrant to host populations. INTERPRETATION: Migrants are exposed to conditions favouring the emergence of drug resistance during transit and in host countries in Europe. Increased antibiotic resistance among refugees and asylum seekers and in high-migrant community settings (such as refugee camps and detention facilities) highlights the need for improved living conditions, access to health care, and initiatives to facilitate detection of and appropriate high-quality treatment for antibiotic-resistant infections during transit and in host countries. Protocols for the prevention and control of infection and for antibiotic surveillance need to be integrated in all aspects of health care, which should be accessible for all migrant groups, and should target determinants of AMR before, during, and after migration. FUNDING: UK National Institute for Health Research Imperial Biomedical Research Centre, Imperial College Healthcare Charity, the Wellcome Trust, and UK National Institute for Health Research Health Protection Research Unit in Healthcare-associated Infections and Antimictobial Resistance at Imperial College London
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