124 research outputs found
Strong effects of uniaxial pressure and short-range correlations in Cr2Ge2Te6
Cr2Ge2Te6 is a quasi-two-dimensional semiconducting van der Waals ferromagnet down to the bilayer with great potential for technological applications. Engineering the critical temperature to achieve room-temperature applications is one of the critical next steps on this path. Here, we report high-resolution capacitance dilatometry studies on Cr2Ge2Te6 single crystals which directly prove significant magnetoelastic coupling and provide quantitative values of the large uniaxial pressure effects on long-range magnetic order (âTC/âpc=24.7 K/GPa and âTC/âpab=â15.6 K/GPa) derived from thermodynamic relations. Moderate in-plane strain is thus sufficient to strongly enhance ferromagnetism in Cr2Ge2Te6 up to room temperature. Moreover, unambiguous signs of short-range magnetic order up to 200 K are found
A primer on provenance
Better understanding data requires tracking its history and context.</jats:p
Magnetic anisotropy and low-energy spin dynamics in the van der Waals compounds MnPS and MnNiPS
We report the detailed high-field and high-frequency electron spin resonance
(HF-ESR) spectroscopic study of the single-crystalline van der Waals compounds
MnPS and MnNiPS. Analysis of magnetic excitations
shows that in comparison to MnPS increasing the Ni content
yields a larger magnon gap in the ordered state and a larger g-factor value and
its anisotropy in the paramagnetic state. The studied compounds are found to be
strongly anisotropic having each the unique ground state and type of magnetic
order. Stronger deviation of the g-factor from the free electron value in the
samples containing Ni suggests that the anisotropy of the exchange is an
important contributor to the stabilization of a certain type of magnetic order
with particular anisotropy. At temperatures above the magnetic order, we have
analyzed the spin-spin correlations resulting in a development of slowly
fluctuating short-range order. They are much stronger pronounced in
MnNiPS compared to MnPS. The enhanced spin
fluctuations in MnNiPS are attributed to the competition of
different types of magnetic order. Finally, the analysis of the temperature
dependent critical behavior of the magnon gaps below the ordering temperature
in MnPS suggests that the character of the spin wave
excitations in this compound undergoes a field induced crossover from a 3D-like
towards 2D XY regime
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Intertwined electronic and magnetic structure of the van-der-Waals antiferromagnet Fe2P2S6
Many unusual and promising properties have been reported recently for the transition metal trichalcogenides of the type MPS3 (M = V, Mn, Fe, Ni..), such as maintaining magnetic order to the atomically thin limit, ultra-sharp many-body excitons, metal-insulator transitions and, especially for Fe2P2S6, giant linear dichroism among others. Here we conduct a detailed investigation of the electronic structure of Fe2P2S6 using angle-resolved photoemission spectroscopy, q-dependent electron energy loss spectroscopy, optical spectroscopies and density functional theory. Fe2P2S6 is a Mott insulator with a gap of E gap â 1.4 eV and zigzag antiferromagnetism below T N = 119 K. The low energy excitations are dominated by Fe 3d states. Large and sign-changing linear dichroism is observed. We provide a microscopic mechanism explaining key properties of the linear dichroism based on the correlated character of the electronic structure, thereby elucidating the nature of the spin-charge coupling in Fe2P2S6 and related materials
Evolution of the spin dynamics in the van der Waals system PS ( = Mn, MnNi, Ni) series probed by electron spin resonance spectroscopy
In this work we report a detailed ESR spectroscopic study of the
single-crystalline samples of the van der Waals compounds
PS ( = Mn,
MnNi, Ni), performed at an excitation frequency of 9.56 GHz, in a
broad range of temperatures above the magnetic order, and at different
orientations of the magnetic field with respect to the sample. Analyzing
temperature and angular dependences of the resonance field and of the linewidth
of the MnPS compound we have observed a significant change of the
spin dynamics from the dominance of the 3D-like fluctuations close to the
magnetic order to a relative increase of the 2D-like spin fluctuations at
higher temperatures. Such a behavior, which is opposite to the development of
the low-D signatures in the previously studied
CrGeTe compound, can be explained by the
difference in the type of magnetic order in MnPS and
CrGeTe. On the other hand,
MnNiPS compound exhibits angular dependences of the linewidth typical
for the system with 3D-like spin correlations in the whole measurement
temperature range, however the 2D-like correlations can be seen in the
temperature dependences of the resonance field and the linewidth.
NiPS, in turn, does not show any 2D signatures. This suggests that
varying the Ni content in (MnNi)PS one can control the
exchange interaction, possibly also in the third dimension
Crystal growth, characterization and electronic band structure of TiSeS
Layered semimetallic van der Waals materials TiSe2 has attracted a lot of
attention because of interplay of a charge density wave (CDW) state and
superconductivity. Its sister compound TiS2, being isovalent to TiSe2 and
having the same crystal structure, shows a semiconducting behavior. The natural
rises what happens at the transition point in TiSe2-xSx, which is expected for
x close to 1. Here we report the growth and characterization of TiSeS single
crystals and the study of the electronic structure using density functional
theory (DFT) and angle-resolved photoemission (ARPES). We show that TiSeS
single crystals have the same morphology as TiSe2. Transport measurements
reveal a metallic state, no evidence of CDW was found. DFT calculations suggest
that the electronic band structure in TiSeS is similar to that of TiSe2, but
the electron and hole pockets in TiSeS are much smaller. The ARPES results are
in good agreement with the calculations.Comment: 22 pages, 9 figure
Fatigue in multiple sclerosis: Associations with clinical, MRI and CSF parameters
Background: Damage of different brain structures has been related to fatigue. Alternatively, functional alterations of central nervous system (CNS) cells by the inflammatory milieu within the CNS may be responsible for the development of fatigue. Aim: To investigate the effect of structural brain damage and inflammatory cerebrospinal fluid (CSF) changes on fatigue in multiple sclerosis (MS). Methods: We determined the association of different clinical, CSF and magnetic resonance imaging (MRI) parameters with prevalence and severity of fatigue, as measured by the Fatigue Scale for Motor and Cognitive Functions in 68 early MS patients (discovery cohort). We validated our findings in two MS cohorts: the MRI validation cohort (N=233) for the clinical and MRI parameters, and the CSF validation cohort (N=81) for the clinical and CSF parameters. Results: Fatigue was associated with clinical disability. Fatigue did not correlate with any CSF parameter but correlated negatively with total and cortical grey matter volume. However, when controlling for Expanded Disability Status Scale (EDSS) in a multivariate model, these associations lost significance. Conclusion: Disability and disease duration best explain fatigue severity but none of the tested MRI or CSF parameter was reliably associated with fatigue
Ancestry of Pink Disease (Infantile Acrodynia) Identified as a Risk Factor for Autism Spectrum Disorders
Pink disease (infantile acrodynia) was especially prevalent in the first half of the 20th century. Primarily attributed to exposure to mercury (Hg) commonly found in teething powders, the condition was developed by approximately 1 in 500 exposed children. The differential risk factor was identified as an idiosyncratic sensitivity to Hg. Autism spectrum disorders (ASD) have also been postulated to be produced by Hg. Analogous to the pink disease experience, Hg exposure is widespread yet only a fraction of exposed children develop an ASD, suggesting sensitivity to Hg may also be present in children with an ASD. The objective of this study was to test the hypothesis that individuals with a known hypersensitivity to Hg (pink disease survivors) may be more likely to have descendants with an ASD. Five hundred and twenty-two participants who had previously been diagnosed with pink disease completed a survey on the health outcomes of their descendants. The prevalence rates of ASD and a variety of other clinical conditions diagnosed in childhood (attention deficit hyperactivity disorder, epilepsy, Fragile X syndrome, and Down syndrome) were compared to well-established general population prevalence rates. The results showed the prevalence rate of ASD among the grandchildren of pink disease survivors (1 in 25) to be significantly higher than the comparable general population prevalence rate (1 in 160). The results support the hypothesis that Hg sensitivity may be a heritable/genetic risk factor for ASD
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