Magnon-magnon interaction in monolayer MnBi2_2Te4_4

MnBi$_2$Te$_4$, the first confirmed intrinsic antiferromagnetic topological insulator, have attracted more and more attention in recent years. Here we investigate the energy correction and lifetime of magnons in MnBi$_2$Te$_4$ caused by magnon-magnon interaction. Firstly, a first-principles calculation was performed to get the parameters of the magnetic Hamiltonian of MnBi$_2$Te$_4$. Then the perturbation method of many-body Green's function is applied and the 1st-order self-energy [$\Sigma^{(1)}({\bf k})$] and 2nd-order self-energy [$\Sigma^{(2)}({\bf k},\varepsilon_{\bf k})$] of magnon are obtained. Numerical computation shows that the correction from both $\Sigma^{(1)}({\bf k})$ and $\Sigma^{(2)}({\bf k},\varepsilon_{\bf k})$ are strongly dependent on momentum and temperature, the energy renormalization near Brillouin zone (BZ) boundary is obviously stronger than that near BZ centre. We also find that some dip structures occur in renormalized magnon spectrum near $\rm K$ and $\rm M$ points, and these dip structures should be attributed to $\Sigma^{(2)}({\bf k},\varepsilon_{\bf k})$.Comment: 7 pages, 7 figure

Magnetic interactions and possible structural distortion in kagome FeGe from first-principles study and symmetry analysis

Based on density functional theory and symmetry analysis, we present a comprehensive investigation of electronic structure, magnetic properties and possible structural distortion of magnetic kagome metal FeGe. We estimate the magnetic parameters including Heisenberg and Dzyaloshinskii-Moriya (DM) interactions, and find that the ferromagnetic nearest-neighbor $J_{1}$ dominates over the others, while the magnetic interactions between nearest kagome layers favors antiferromagnetic. The N\'{e}el temperature $T_{N}$ and Curie-Weiss temperature $\theta _{CW}$ are successfully reproduced, and the calculated magnetic anisotropy energy is also in consistent with the experiment. However, these reasonable Heisenberg interactions and magnetic anisotropy cannot explain the double cone magnetic transition, and the DM interactions, which even exist in the centrosymmetric materials, can result in this small magnetic cone angle. Unfortunately, due to the crystal symmetry of the high-temperature structure, the net contribution of DM interactions to double cone magnetic structure is absent. Based on the experimental $2\times 2\times 2$ supercell, we thus explore the subgroups of the parent phase. Group theoretical analysis reveals that there are 68 different distortions, and only four of them (space group $P622$ or $P6_{3}22$) without inversion and mirror symmetry thus can explain the low-temperature magnetic structure. Furthermore, we suggest that these four proposed CDW phases can be identified by using Raman spectroscopy. Since DM interactions are very sensitive to small atomic displacements and symmetry restrictions, we believe that symmetry analysis is an effective method to reveal the interplay of delicate structural distortions and complex magnetic configurations

Studies on Chemical Constituents of Radix Angelicae pubescentis

Backgound:Angelicae pubescentis is the root of Angelica pubescens Maxim. f. biserrata Shan et Yuan. The main active ingredients are coumarin and volatile oil, and it has a variety of pharmacological activities such as antibacterial, antioxidant and anti-inflammatory. In this paper, the active components of the CO2 supercritical extract of Angelicae pubescentis were studied. The results of this study will provide a scientific basis for the study of the chemical composition of Angelicae pubescentis. Purpose: To study the chemical constituents of supercritical extract of Radix Angelicae pubescentis. Method: The supercritical extract of Radix Angelicae pubescentis was separated by silica gel column chromatography to obtain monomers. The structures were identified based on physicochemical properties and spectroscopic data. Result: Eight compounds were separated from the supercritical extract of Radix Angelicae pubescentis, six of which were identified.They are Osthol, Columbianedin, Columbianetin, Columbianetin Acetate, Xanthotoxin and Bergapten. Conclusion: Xanthotoxin and Bergapten were isolated, which structure were similar. The standard substance of Osthol and Columbianedin were producted in order to offer the good material base for quality evaluation and pharmacodynamic study of Radix Angelicae pubescentis. Their purification were more than 99%. The results of this study are of great significance for exploring the effective material basis and medicinal value of the supercritical extract of Radix Angelicae pubescentis

Microstructure Evolution and Mechanical Properties of Ferrite–Austenite Duplex Fe-Mn-Al-(Cu)-C Steel under Different Annealing Temperatures

The effect of Cu addition and the intercritical annealing (IA) temperature on the microstructural evolution and mechanical properties of Fe-0.4C-7Mn-4Al (wt%) was investigated via scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), X-ray diffraction (XRD) and nanoindentation tests. The results showed that the volume fraction and the average grain size of austenite, and the fraction of high angle grain boundaries, increased with IA temperature increase in the range of 650 °C to 710 °C. The addition of Cu facilitates the formation of Cu-rich nanoparticles, raises the volume fraction of austenite, and delays the recrystallization of austenite. As IA temperature increased, the yield strength (YS), ultimate tensile strength (UTS), and Lüders bands strain (LBS) decreased in both experimental steels. The Cu addition not only increases the YS of medium Mn steel but also benefits the decrease of LBS. The best comprehensive mechanical properties were obtained at the IA temperature of 690 °C in the studied steel, with Cu addition. According to nanoindentation experiments, the Cu addition raises the hardness of ferrite and austenite from 4.7 GPa to 6.3 GPa and 7.4 GPa to 8.5 GPa, respectively, contributing to the increase of YS of medium-Mn steel