Hybridization and Decay of Magnetic Excitations in two-dimensional Triangular Lattice Antiferromagnets

Elementary quasiparticles in solids such as phonons and magnons occasionally have nontrivial interactions between them, as well as among themselves. As a result, their energy eigenvalues are renormalized, the quasiparticles spontaneously decay into a multi-particle continuum state, or they are hybridized with each other when their energies are close. As discussed in this review, such anomalous features can appear dominantly in quantum magnets but are not, a priori, negligible for magnetic systems with larger spin values and noncollinear magnetic structures. We review the unconventional magnetic excitations in two-dimensional triangular lattice antiferromagnets and discuss their implications on related issues.Comment: 18 pages, 9 figure

EFFECTS OF MO, CR, AND V ADDITIONS ON TENSILE AND CHARPY IMPACT PROPERTIES OF API X80 PIPELINE STEELS

In this study, four API X80 pipeline steels were fabricated by varying Mo, Cr, and V additions, and their microstructures and crystallographic orientations were analyzed to investigate the effects of their alloying compositions on tensile properties and Charpy impact properties. Because additions of Mo and V promoted the formation of fine acicular ferrite (AF) and granular bainite (GB) while prohibiting the formation of coarse GB, they increased the strength and upper-shelf energy (USE) and decreased the energy transition temperature (ETT). The addition of Cr promoted the formation of coarse GB and hard secondary phases, thereby leading to an increased effective grain size, ETT, and strength, and a decreased USE. The addition of V resulted in a higher strength, a higher USE, a smaller effective grain size, and a lower ETT, because it promoted the formation of fine and homogeneous of AF and GB. The steel that contains 0.3 wt pct Mo and 0.06 wt pct V without Cr had the highest USE and the lowest ETT, because its microstructure was composed of fine AF and GB while its maintained excellent tensile properties.X1126sciescopu

Suppression of magnetic ordering in XXZ-type antiferromagnetic monolayer NiPS3

How a certain ground state of complex physical systems emerges, especially in two-dimensional materials, is a fundamental question in condensed-matter physics. A particularly interesting case is systems belonging to the class of XY Hamiltonian where the magnetic order parameter of conventional nature is unstable in two-dimensional materials leading to a Berezinskii-Kosterlitz-Thouless transition. Here, we report how the XXZ-type antiferromagnetic order of a magnetic van der Waals material, NiPS3, behaves upon reducing the thickness and ultimately becomes unstable in the monolayer limit. Our experimental data are consistent with the findings based on renormalization group theory that at low temperatures a two-dimensional XXZ system behaves like a two-dimensional XY one, which cannot have a long-range order at finite temperatures. This work provides experimental examination of the XY magnetism in the atomically thin limit and opens new opportunities of exploiting these fundamental theorems of magnetism using magnetic van der Waals materials.Comment: 57 pages, 24 figures (including Supplementary Information

Chronic physical exercise alleviates stress-associated amygdala metabolic activity in obese women: A prospective serial 18F-FDG PET/CT study

BackgroundPsychological stress is considered as a major risk factor for cardiovascular disease (CVD). Chronic exercise is known to reduce CVD risk partly through attenuating psychological stress. Obesity has been linked with increased levels of psychological stress. We aimed to prospectively evaluate whether physical exercise could alleviate stress-associated amygdala metabolic activity, assessed by 18F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) in women with obesity.Material and methodsA total of 43 participants were enrolled in this study. Twenty-three obese women were participated in a physical exercise program 5 days per week for 3 months. The exercise program consisted of aerobic exercise and resistance training. Serial 18F-FDG PET/CT was taken before the start of physical exercise program (baseline) and after finishing the program (post-exercise). A total of 20 participants who underwent 18F-FDG PET/CT for general health check-up were enrolled as non-obese control group. Brain amygdala activity (AmygA) was calculated as maximum standardized uptake value (SUVmax) of amygdala normalized to mean SUV of temporal lobe.ResultsChronic physical exercise significantly reduced AmygA and improved body adiposity and systemic inflammation. AmygA was highest in baseline, intermediate in post-exercise, and lowest in non-obese control group (0.76 ± 0.17, 0.61 ± 0.1, 0.52 ± 0.09, p < 0.001). Furthermore, physical exercise also abrogated the association of AmygA with systemic inflammation.ConclusionsChronic physical exercise reduced stress-associated amygdala metabolic activity and broke its association with systemic inflammation in obese women. This study could explain the putative mechanism underlying the health beneficial effect of exercise on CVD via attenuation of stress neurobiology

Association between district-level perceived safety and self-rated health: A multilevel study in Seoul, South Korea

Objectives Several studies have reported the relationship between residents’ perceived neighbourhood safety and their health outcomes. However, those studies suffered from unreliability of neighbourhood safety measure and potential residual confounding related to crime rates. In this study, using multilevel analysis to account for the hierarchical structure of the data, we examined associations between district-level perceived safety and self-rated health after adjusting for potential confounders including the district-level crime rate. Design Cross-sectional study. Setting We used the first wave of Seoul Welfare Panel Study, which has 7761 individuals from 3665 households in 25 administrative districts in Seoul, South Korea. District-level perceived safety was obtained by aggregating responses from the residents that are representative samples for each administrative district in Seoul. To examine an association between district-level safety and residents’ self-rated health, we used mixed effect logistic regression. Results Our results showed that higher district-level perceived safety, an aggregated measure of district residents’ responses towards neighbourhood safety, was significantly associated with poor self-rated health after controlling for sex, age, education level, job status, marital status and household income (OR=0.87, 95% CI 0.78 to 0.97). Furthermore, this association was still robust when we additionally adjusted for the district-level crime rate (OR=0.86, 95% CI 0.77 to 0.95). Conclusions Our study highlights the importance of improving neighbourhood perceived safety to enhance residents’ health

Renormalization of spin excitations in hexagonal HoMnO3 by magnon-phonon coupling

Hexagonal HoMnO3, a two-dimensional Heisenberg antiferromagnet, has been studied via inelastic neutron scattering. A simple Heisenberg model with a single-ion anisotropy describes most features of the spin-wave dispersion curves. However, there is shown to be a renormalization of the magnon energies located at around 11 meV. Since both the magnon-magnon interaction and magnon-phonon coupling can affect the renormalization in a noncollinear magnet, we have accounted for both of these couplings by using a Heisenberg XXZ model with 1=S expansions [1] and the Einstein site phonon model [13], respectively. This quantitative analysis leads to the conclusion that the renormalization effect primarily originates from the magnon-phonon coupling, while the spontaneous magnon decay due to the magnon-magnon interaction is suppressed by strong two-ion anisotropy.Comment: 5 pages, 4 figure

Spin-orbit coupling effects on spin-phonon coupling in Cd2Os2O7

Spin-orbit coupling (SOC) is essential in understanding the properties of 5d transition metal compounds, whose SOC value is large and almost comparable to other key parameters. Over the past few years, there have been numerous studies on the SOC-driven effects of the electronic bands, magnetism, and spin-orbit entanglement for those materials with a large SOC. However, it is less studied and remains an unsolved problem in how the SOC affects the lattice dynamics. We, therefore, measured the phonon spectra of 5d pyrochlore Cd2Os2O7 over the full Brillouin zone to address the question by using inelastic x-ray scattering (IXS). Our main finding is a visible mode-dependence in the phonon spectra, measured across the metal-insulator transition at 227 K. We examined the SOC strength dependence of the lattice dynamics and its spin-phonon (SP) coupling, with first-principle calculations. Our experimental data taken at 100 K are in good agreement with the theoretical results obtained with the optimized U = 2.0 eV with SOC. By scaling the SOC strength and the U value in the DFT calculations, we demonstrate that SOC is more relevant than U to explaining the observed mode-dependent phonon energy shifts with temperature. Furthermore, the temperature dependence of the phonon energy can be effectively described by scaling SOC. Our work provides clear evidence of SOC producing a non-negligible and essential effect on the lattice dynamics of Cd2Os2O7 and its SP coupling.Comment: 12 pages, 5 figures, accepted for publication at Rapid Communication in Physical Review

Momentum-dependent magnon lifetime in the metallic non-collinear triangular antiferromagnet CrB2

Non-collinear magnetic order arises for various reasons in several magnetic systems and exhibits interesting spin dynamics. Despite its ubiquitous presence, little is known of how magnons, otherwise stable quasiparticles, decay in these systems, particularly in metallic magnets. Using inelastic neutron scattering, we examine the magnetic excitation spectra in a metallic non-collinear antiferromagnet CrB$_{2}$, in which Cr atoms form a triangular lattice and display incommensurate magnetic order. Our data show intrinsic magnon damping and continuum-like excitations that cannot be explained by linear spin wave theory. The intrinsic magnon linewidth $\Gamma(q,E_{q})$ shows very unusual momentum dependence, which our analysis shows to originate from the combination of two-magnon decay and the Stoner continuum. By comparing the theoretical predictions with the experiments, we identify where in the momentum and energy space one of the two factors becomes more dominant. Our work constitutes a rare comprehensive study of the spin dynamics in metallic non-collinear antiferromagnets. It reveals, for the first time, definite experimental evidence of the higher-order effects in metallic antiferromagnets.Comment: 6 pages, 4 figures, accepted for publication in PR