Weak Anisotropy Research Articles

Weak-anisotropy approximation of P-wave geometric spreading in horizontally layered anisotropic media of arbitrary symmetry: Tilted transversely isotropic specification

Understanding the role of geometric spreading and estimating its effects on seismic wave propagation play an important role in several techniques used in seismic exploration. The spreading can be estimated through dynamic ray tracing or determined from reflection traveltime derivatives. In the latter case, derivatives of nonhyperbolic moveout approximations are often used. We offer an alternative approach based on the weak-anisotropy approximation. The resulting formula is applicable to P-waves reflected from the bottom of a stack of horizontal layers, in which each layer can be of arbitrary anisotropy. At an arbitrary surface point, the formula depends, in each layer, on the thickness of the layer, on the P-wave reference velocity used for the construction of reference rays, and on nine P-wave weak-anisotropy (WA) parameters specifying the layer anisotropy. Along an arbitrary surface profile, the number of WA parameters reduces to five parameters related to the profile. WA parameters represent an alternative to the elastic moduli and, as such, can be used for the description of any anisotropy. The relative error of the approximate formula for a multilayered structure consisting of layers of anisotropy between 8% and 20% is, at most, 10%. For models including layers of anisotropy stronger than 20%, the relative errors may reach, locally, even 30%. For any offset, relative errors remain under a finite limit, which varies with the anisotropy strength.

Effect of surface morphology on magnetization dynamics of cobalt ultrathin films: An in-situ investigation

Growth of Co film on SiO2/Si substrates with surface roughness of 0.5 nm and 1.6 nm have been studied in-situ using magneto-optical Kerr effect (MOKE) and transport measurements. In-situ measurements jointly suggest that the films grow via Volmer-Weber growth process and proceed via a nonmagnetic, superparamagnetic and a ferromagnetic phase formation on both the substrates. Islands are found to coalesce at film thicknesses ~ 0.6 nm and at ~ 1.5 nm with continuous film formation around film thickness ~1.5 nm and ~ 3.0 nm for smooth and rough substrates, respectively. Ferromagnetic long-range ordering i.e., appearance of magnetic hysteresis loop in both films is observed just after coalesce stage. Observed azimuthal angular dependence of coercivity confirmed the presence of a weak uniaxial magnetic anisotropy (UMA) in both the films, whereas difference in UMA with substrate roughness is interpreted in terms of combined effect of domain wall pinning and internal stresses in the films. Origin of much higher UMA in case of the Co film deposited on ripple patterned substrate of similar root mean square roughness is attributed to the modified long range dipolar stray fields on the surface.

Fluorine-Driven Enhancement of Birefringence in the Fluorooxosulfate: A Deep Evaluation from a Joint Experimental and Computational Study.

Understanding and exploring the functional modules (FMs) consisting of local atomic groups can promote the development of the materials with functional performances. Oxygen‐containing tetrahedral modules are popular in deep‐ultraviolet (DUV) optical materials, but their weak optical anisotropy is adverse to birefringence. Here, the fluorooxosulfate group is proved as a new birefringence‐enhanced FM for the first time. The birefringence of fluorooxosulfates can be 4.8–15.5 times that of sulfates with the same metal cations while maintaining a DUV band gap. The polarizing microscope measurement confirms the birefringence enhancement by using the millimeter crystals experimentally. The theoretical studies from micro and macro levels further reveal a novel universal strategy that the fluorine induced anisotropic electronic distribution in fluorooxo–tetrahedral group is responsible for the enhancement of birefringence. This study will guide the future discovery of DUV optical materials with enlarged birefringence.

Effect of the Alkaline Metal Ion on the Crystal Structure and Magnetic Properties of Heterometallic GdIII-VIV Complexes Based on Cyclobutane-1,1-Dicarboxylate Anions

A series of heterometallic GdIII-VIV compounds were synthesized by the reaction of VOSO4·3H2O with cyclobutane-1,1-dicarboxylic acid salts M2(cbdc) (M = Na, Rb, Cs). The new compounds were formed by [Gd(VO)2(cbdc)4(H2O)8]− trinuclear anionic units that were similar in composition but differed in structure, depending on the nature of the alkali metal cation incorporated in the crystal structure of the compound. In the case of Na+, the {GdV2}− units were characterized by identical V···Gd distances and were linked into the 1D-polymeric chain [NaGd(VO)2(cbdc)4(H2O)10]n (1). In the systems with Rb+ and Cs+, the V···Gd distances were different, and the {GdV2}− units were linked into the 3D-framework {[RbGd(VO)2(cbdc)4(H2O)10]·2.5H2O}n (2) and the octanuclear molecule {[CsGd(VO)2(cbdc)4(H2O)11]·5H2O}2 (3), respectively. According to dc-magnetic measurements, the VIV and GdIII ions were ferromagnetically coupled in compound 1 (JVGd = 0.163 ± 0.008 cm−1), while in compounds 2 and 3, ferro- and weak antiferromagnetic exchange interactions were observed (JVGd = 0.989 ± 0.028 and −0.089 ± 0.008 cm−1 for 2, 0.656 ± 0.009 and −0.050 ± 0.004 cm−1 for 3). Analysis of the EPR spectra of 1 revealed the presence of weak magnetic anisotropy of GdIII ions (D ~ 0.08 cm−1 and E/D ~ 0.1–0.15). Ac-susceptibility measurements showed an occurrence the field-induced slow relaxation of magnetization in 1–3.

Magnetic-field-controlled charge transport in organic polymer composites

Spin properties of charge carriers photoexcited in the P3HT:PC61BM and PCDTBT:PC61BM composites were studied at X-band EPR spectroscopy. Light-induced EPR spectra were deconvoluted and the contributions of all spin charge carriers were determined. The main magnetic resonance parameters of charge carriers obtained were compared with those determined at millimeter EPR wavebands and analyzed as a function of electron precession frequency. The linewidth of spin charge carriers was established to originated mainly due to the weak anisotropy of their g-factors. The external magnetic field significantly affects dynamics, electron relaxation and recombination of spin charge carriers.

Generalized framework of weak-value amplification in path interference of polarized light for the enhancement of all possible polarization anisotropy effects

Using the profound interferometric philosophy of weak value amplification, we propose a simple, general and a robust polarization method for the amplification and quantification of small magnitudes of all possible polarization anisotropy effects in a single experimental embodiment. The approach is experimentally realized by introducing a weak coupling between the polarization degree of freedom of light and the path degree of freedom in a Mach-Zehnder interferometer in the presence of a weak anisotropy effect. Real and imaginary weak value amplifications of different polarization anisotropy effects are manifested as characteristic changes in relevant Stokes vector elements at the exit port of the interferometer, which follow orthogonal trajectories in the Poincare sphere. The proof of concept experiment demonstrates that using this scheme, one can faithfully extract and quantify anisotropy parameter that is smaller than the typical sensitivity of measurement of a given Stokes parameter of a traditional polarimeter by a large weak value amplification factor. This opens up possibility of a sample measuring weak value polarimeter for studying rich variety of fundamental optical effects and for materials characterization and precision metrology.

Estimation of Brittleness and Anisotropy Parameters in Transversely Isotropic Media With Vertical Axis of Symmetry

In the absence of fracture, the strata with horizontal interbedding structure can be approximately equivalent to transversely isotropic media with vertical axis of symmetry (VTI) in the sedimentary basin. Accurate estimation of Young’s modulus, Poisson’s ratio, and weak anisotropy (WA) parameters can provide basic information for further prediction of shale reservoir rock brittleness and <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in situ</i> stress. Based on the scattering theory and Born approximation, we derive the P-wave reflection coefficients involving Young’s modulus and Poisson’s ratio and WA parameters for an interface separating two elastic VTI media. Assuming in the case of shale, we modify this reflection coefficient to involve only three model parameters through a series of integration and simplification for stabler inversion. A Bayesian amplitude versus offset (AVO) inversion method is implemented to estimate the three attributes, which are then converted to calculate the brittleness-related and WA parameters. The numerical simulation results show that for AVO of III in the case of gas-bearing shale, the derived approximation has more accuracy than the Young’s modulus, Poisson’s ratio and density (YPD) equation, especially at large angle. Tests on synthetic and real seismic data verify that the established inversion strategy for VTI shale reservoirs is stable and accurate in the estimation of brittleness-related and WA parameters.

Spirals and skyrmions in antiferromagnetic triangular lattices

We study realizations of spirals and skyrmions in two-dimensional antiferromagnets with a triangular lattice on an inversion-symmetry-breaking substrate. As a possible material realization, we investigate the adsorption of transition-metal atoms (Cr, Mn, Fe, or Co) on a monolayer of MoS$_2$, WS$_2$, or WSe$_2$ and obtain the exchange, anisotropy, and Dzyaloshinskii-Moriya interaction parameters using first-principles calculations. Using energy minimization and parallel-tempering Monte-Carlo simulations, we determine the magnetic phase diagrams for a wide range of interaction parameters. We find that skyrmion lattices can appear even with weak Dzyaloshinskii-Moriya interactions, but their stability is hindered by magnetic anisotropy. However, a weak easy plane magnetic anisotropy can be beneficial for stabilizing the skyrmion phase. Our results suggest that Cr$/$MoS$_2$, Fe$/$MoS$_2$, and Fe$/$WSe$_2$ interfaces can host spin spirals formed from the 120$^{\circ}$ antiferromagnetic states. Our results further suggests that for other interfaces, such as Fe$/$MoS$_2$, the Dzyaloshinskii-Moriya interaction is strong enough to drive the system into a three-sublattice skyrmion lattice in the presence of experimentally feasible external magnetic field.

Remarkably Weak Anisotropy in Thermal Conductivity of Two-Dimensional Hybrid Perovskite Butylammonium Lead Iodide Crystals.

Two-dimensional (2D) hybrid organic-inorganic perovskites consisting of alternating organic and inorganic layers are a new class of layered structures. They have attracted increasing interest for photovoltaic, optoelectronic, and thermoelectric applications, where knowing their thermal transport properties is critical. We carry out both experimental and computational studies on thermal transport properties of 2D butylammonium lead iodide crystals and find their thermal conductivity is ultralow (below 0.3 W m-1 K-1) with very weak anisotropy (around 1.5) among layered crystals. Further analysis reveals that the unique structure with the preferential alignment of organic chains and complicated energy landscape leads to moderately smaller phonon lifetimes in the out-of-plane direction and comparable phonon group velocities in in-plane and out-of-plane directions. These new findings may guide the future design of novel hybrid materials with desired thermal conductivity for various applications.

Strength differential effect and anisotropy of Mg–1.9Mn–0.3Ce (wt-%) alloy subjected to high-rate loadings

Tension and compression tests for a rare-earth-containing alloy sheet, Mg–1.9Mn–0.3Ce (wt-%), are performed under quasi-static and high-rate loadings along the rolling, transverse and normal direction, and stress – strain responses exhibit positive strain-rate dependence. Empirically based Johnson-Cook constitutive model is modified to describe the rate-dependent plastic deformation in multiple loading directions. A strong strength differential effect persists, and such effect is shown to be stronger at high strain rates. A weak in-plane anisotropy exists in the initial yielding and subsequent strain hardening behaviour as well as strength differential effect. In contrast, the out-of-plane anisotropy in compression is apparent and is approximately rate insensitive. Microstructural observations indicate that twinning plays the key role for the enhancement of strain-hardening rate under high strain-rate deformation.

Mantle Flow and Dynamics Beneath Central‐East China: New Insights From P‐Wave Anisotropic Tomography

AbstractMassive lithospheric thinning occurred in eastern China and large‐scale magmatism in South China occurred in the Mesozoic. Some geodynamic models have been proposed to explain their mechanisms, but are not consistent with each other. We apply anisotropic tomography to 32,728 P‐wave travel time data of 479 teleseismic events recorded at 225 stations to study the 3‐D anisotropic Vp structure of the upper mantle beneath central‐east China. P‐wave radial anisotropy is investigated for the first time in the study region. Our results show that an obvious low‐velocity zone exists in the asthenosphere under the eastern part of our study region, which represents upwelling thermal flow from the Cathaysia block to the North China block (NCB) according to the results of azimuthal and radial anisotropies. A distinct high‐velocity zone with weak radial anisotropy exists under the middle Yangtze block, which is explained as the stable cratonic root. Two other weak high‐velocity zones appear near or within the mantle transition zone under the middle‐lower Yangtze River and the eastern NCB, which might be detached lithosphere or the stagnant Pacific slab. Combining with previous geological and geochemical results, we consider that both the NCB and the South China block have undergone a common geodynamic process in the Mesozoic due to their similar age trending of igneous rocks, which could be explained by a flat‐slab subduction model and a ridge subduction model. These two models are associated with the paleo‐Pacific plate subduction that might have played a key role in the evolution of eastern China.

Seismic anisotropy and implications for lithospheric deformation beneath the Ordos Block and surrounding regions

SUMMARYThe Ordos Block is located at the intersection of the Tibetan Plateau, the South China Plate and the North China Craton. The deep deformation of its surrounding areas is geologically complicated. Seismic anisotropy provides information about past and present deformation of the upper mantle and helps to better understand deep deformation processes. We obtained the anisotropic pattern at high resolution within and surrounding the Ordos Block by analysing teleseismic data from ∼710 newly deployed temporary seismic stations based on SKS phases from ∼86 earthquakes. The central and eastern Ordos Block with a relatively thick and rigid lithosphere is characterized by a weak anisotropy. In the western part of the Ordos Block, the fast-wave polarization direction is dominantly NW–SE. We believe the lithosphere in the western part of the Ordos Block may have undergone significant deformation caused by expansion and compression of the Tibetan Plateau. Near the Datong Basin, the delay time is 0.92 s and the fast-wave polarization direction is mainly oriented NW–SE, perpendicular to the NE-directed compression of the Tibetan Plateau and parallel to the basin extension direction. We speculate that this anisotropy is related to the long-range effect of NE compression of the northeastern Tibetan Plateau on the low-velocity upper mantle in this area. The weak anisotropy in the central part of the Shanxi Rift indicates that the thickness and mechanical strength of the high-velocity lithosphere are higher than in the southern and northern regions.

Comparison of in-source solid bitumen with migrated solid bitumen from Ediacaran-Cambrian rocks in the Upper Yangtze region, China

In-source solid bitumen was found in some cracks within the calcareous concretion in an overmature (Rbitumen > 3.5%) black shale of the Lower Cambrian Niutitang Formation from Songtao, Guizhou, China. The solid bitumen (grain size >2 cm) concentrated in source rock, which was formed by the transformation of petroleum-like substances that have not been expelled from source rock. This provides a substitute for studying the physical and chemical properties of in-situ solid bitumen, which usually occurs as finely dispersed particles in black shale. On the other hand, Ediacaran-Cambrian carbonate rocks (which serve as reservoir in the area) contain pyrobitumen derived from petroleum that migrated from the black shale of the Niutitang Formation.A comparative petrological and geochemical analysis was conducted on the in-source solid bitumen from the Lower Cambrian Niutitang Formation and the migrated solid bitumen in the Ediacaran-Cambrian carbonate rocks. The in-source solid bitumen displays a relatively homogeneous optical structure with very weak anisotropy and is visibly different from the migrated bitumen in the Ediacaran-Cambrian carbonate reservoir. This migrated bitumen in the reservoir displays strong anisotropy and optical structure similar to that of coke. Considering a strata like the lower Palaeozoic in South China, which has no vitrinite and is highly over mature, the in-source solid bitumen is likely to be the most suitable organic component for measuring the reflectance and subsequently determining the thermal maturity of organic matter.Interestingly, the in-source solid bitumen displays some inheritance of its parent material. The stable carbon isotope ratios are very similar to those of kerogen in the black shales (approximately −34‰ to −33‰), and the distribution pattern of the trace elements and rare earth elements (REEs) is consistent with that of the Niutitang black shales. The distribution patterns of the trace elements and REEs in the migrated bitumen are basically consistent with those of in-source solid bitumen, however, their stable carbon isotope composition is slightly heavier (−33.6‰ to −31.2‰) than that in the source rocks. In other words, as a key link in the chain, the in-source solid bitumen could connect the migrated bitumen in the reservoir with its source rock. This provides direct support for tracing oil and gas sources in the area by using the element geochemical characteristics of migrated solid bitumen in reservoir.

Stability, Elastic and Electronic Properties of Ta2N by First-Principles Calculations

Owing to exploring the influence of the N atoms ordering in Ta2N compounds on their properties, the stability, elastic, and electronic properties of Ta2N compounds (Ta2N-I: P3¯ml and Ta2N-II: P3¯1m) were investigated using first-principles calculations based on density functional theory. Ta2N-II is energetically favorable according to the enthalpy of formation. Elastic constants were employed to reveal the stronger resistance to deformation, but weaker anisotropy, in Ta2N-II. A ductile-brittle transition was found between Ta2N-I (ductile) and Ta2N-II (brittle). The partial density of states showed a stronger orbital hybridization of Ta-d and N-p in Ta2N-II, resulting in stronger covalent bonding. The charge density difference illustrated the interaction of the Ta-N bond and electron distribution of Ta2N.

Magnetic Anisotropy in a Cubane-like Ni4 Complex: An Ab Initio Perspective.

Magnetic anisotropy, in the absence of an external magnetic field, relates to the degeneracy lift of energy levels. In the standard case of transition metal complexes, this property is usually modeled by an anisotropic spin Hamiltonian and one speaks of "zero-field splitting" (ZFS) of spin states. While the case of mononuclear complexes has been extensively described by means of ab initio quantum mechanical calculations, the literature on polynuclear complexes studied with these methodologies is rather scarce. In this work, advanced multiconfigurational wave function theory methods are applied to compute the ZFS of the ground S = 4 state of an actual tetranickel(II) complex, displaying a magnet behavior below 0.5 K. First, the isotropic couplings are computed in the absence of the spin-orbit coupling operator, in the full complex and also in clusters with only two active nickel(II) centers, confirming the occurrence of weak ferromagnetic couplings in this system. Second, the single-site magnetic anisotropies are computed on a cluster bearing only one active nickel(II) site, showing that the single-site anisotropy axes are not oriented in an optimal fashion for generating a large uniaxial molecular anisotropy. Furthermore, the possibility for involving only a few local orbital excited states in the calculation is assessed, actually opening the way for a consistent and manageable treatment of the ZFS of the ground S = 4 state. Third, multiconfigurational calculations are performed on the full complex, confirming the weak uniaxial anisotropy occurring for this state and also, interestingly, revealing a significant contribution of the lowest-lying orbitally excited S = 3 states. Overall, by comparison with the experiment, the reported results question the common habit of using only one structure, in particular derived from a crystallography experiment, to compute magnetic anisotropy parameters.

Electronic structure, dynamic stability, elastic, and optical properties of MgTMN2 (TM = Ti, Zr, Hf) ternary nitrides from first-principles calculations

Ternary nitride semiconductors with tunable electronic structure and charge transport properties have attracted increasing attention as optoelectronic materials. The recently discovered ternary MgTMN2 (TM=Ti,Zr,Hf) are predicted to be nondegenerate semiconductors with visible-range optical absorption onsets. In the present study, the electronic structure, elastic properties, optical absorption spectrum, and dynamic stability of the MgTMN2 system have been systematically studied by first-principles calculations based on the density functional theory. These compounds show semiconductor characteristics with a bandgap ranging from 1.0 to 1.5 eV predicted by the Heyd–Scuseria–Ernzerhof approach. Compared to the traditional semiconductors of Si and GaAs and III–V nitrides of GaN and AlN, these ternary nitrides have stronger resistance to external compression, shear strain, and deformation due to the larger elastic modulus. MgTiN2 shows a strong anisotropy characteristic along the xy plane and z axis, while for MgZrN2 and MgHfN2, a weak elastic anisotropy is predicted. The absorption regions of these compounds are mainly concentrated in the ultraviolet region, and MgTiN2 is more sensitive to visible light with respect to the other two compounds. The thermodynamic stability of MgTiN2, MgZrN2, and MgHfN2 is verified by the stable phonon dispersion relations. It is found that the most stable low Miller index surface is (110) for MgTiN2 and (100) for MgZrN2 and MgHfN2.

Ultra-fast growth of cuprate superconducting films: Dual-phase liquid assisted epitaxy and strong flux pinning

Cuprate superconductors are key candidate materials toward high energy-efficient devices. Improving their growth rate and performance under magnetic fields are indispensable for achieving even higher efficiency. For the first time, we demonstrated the ultra-high rate up to 100 nm/s in the growth of dual-phase cuprate superconducting film (EuBa2Cu3O7-BaHfO3). The growth rate achieved is two orders of magnitude higher than that at lab-scale and was also the highest on record to our best knowledge. Epitaxial growth mechanism assisted by the transient liquid phase is proposed, as evidenced by formation of Eu2BaCuO5 and Ba–Cu–O metastable phases under high supersaturation conditions. The high growth rate results in formation of mixed defective landscape, consisting of short nanorods, nanoparticles and naturally formed defects (e.g., staking faults). Due to such unique microstructure, we confirm that weak Jc anisotropy is dominated by random pinning mechanism. Contribution of isotropic and anisotropic Jc to Jctotal also varies with temperatures and magnetic field strength, which is a consequence of evolution of dominant pinning in film. As a result, the in-field current carrying capacity is significantly enhanced (exceeding 430 A/4 mm-width at 4.2 K, 18 T, B//c), being among the top tier of commercialized superconductor materials. This study establishes the correlation between ultra-high growth rate and flux pinning behaviors, which provides feasibility of dramatically improvement of production efficiency with the low price-performance ratio of future high temperature superconductor.

Insight into the structural stability and overall performances of V2REAl20 ternary phases

In order to expand the applications of aluminum alloy, the ternary aluminum-based intermetallics have attracted the attentions of scientists. In present work, the overall performances of V2REAl20 (RE = Ho, Gd, Ce, La, Y, and Sc) were explored by DFT investigations. The thermodynamic data, lattice vibrations and volume change curves illustrate that six ternary phases are structurally stable. The values of elastic modulus and elastic constants demonstrate that V2REAl20 compounds display the better mechanical properties than aluminum. The 3D and 2D curves constructions and anisotropic indexes explain that V2REAl20 compounds possess the weak anisotropy. Moreover, the thermodynamic curves indicate that ternary V2REAl20 compounds have the better physical properties than aluminum with the elevated temperatures. In the meantime, we provided the discussion in comparison to the results of ternary Ti2REAl20 compounds.

Bianchiniite, Ba2(Ti4+V3+)(As2O5)2OF, a new diarsenite mineral from the Monte Arsiccio mine, Apuan Alps, Tuscany, Italy

AbstractThe new mineral bianchiniite, Ba2(Ti4+V3+)(As2O5)2OF, has been discovered in the Monte Arsiccio mine, Apuan Alps, Tuscany, Italy. It occurs as brown {001} tabular crystals, up to 1 mm across, with a vitreous lustre. It is brittle, with a perfect {001} cleavage. Streak is brownish. In reflected light, bianchiniite is grey, with orange–yellow internal reflections. It is weakly bireflectant, with a very weak anisotropy in shades of grey. Minimum and maximum reflectance data for COM wavelengths [Rmin/Rmax(%), (λ, nm)] are: 5.0/5.8 (470), 5.7/6.5 (546), 5.7/7.0 (589) and 5.2/6.3 (650). Electron microprobe analyses gave (wt.% – average of 10 spot analyses): TiO210.34, V2O33.77, Fe2O33.76, As2O344.36, Sb2O30.22, SrO 0.45, BaO 34.79, PbO 0.28, F 1.77, sum 99.74, –O = F –0.75, total 98.99. On the basis of 12 anions per formula unit, the empirical formula of bianchiniite is (Ba2.00Sr0.04Pb0.02)Σ2.06(Ti4+1.14V3+0.44Fe3+0.42)Σ2.00[(As3.96Sb0.02)Σ3.98O10](O1.18F0.82)Σ2.00. Bianchiniite is tetragonal, space groupI4/mcm, with unit-cell parametersa= 8.7266(4),c= 15.6777(7) Å,V= 1193.91(12) Å3andZ= 8. Its crystal structure was refined from single-crystal X-ray diffraction data toR1= 0.0134 on the basis of 555 unique reflections withFo&gt; 4σ(Fo) and 34 refined parameters. The crystal structure shows columns of corner-sharing [Ti/(V,Fe)]-centred octahedra running alongc, connected alongaandbthrough (As2O5) dimers. A {001} layer of Ba-centred [10+2]-coordinated polyhedra is intercalated between (As2O5) dimers. Bianchiniite has structural relations with fresnoite- and melilite-group minerals. The name honours the two mineral collectors Andrea Bianchini (b. 1959) and Mario Bianchini (b. 1962) for their contribution to the knowledge of the mineralogy of pyrite ± baryte ± iron-oxide ore deposits from the Apuan Alps.

Isotropic Nature of the Metallic Kagome Ferromagnet Fe3Sn2 at High Temperatures.

Anisotropy and competing exchange interactions have emerged as two central ingredients needed for centrosymmetric materials to exhibit topological spin textures. Fe3Sn2 is thought to have these ingredients as well, as it has recently been discovered to host room temperature skyrmionic bubbles with an accompanying topological Hall effect. We present small-angle inelastic neutron scattering measurements that unambiguously show that Fe3Sn2 is an isotropic ferromagnet below to at least 480 K - the lower temperature threshold of our experimental configuration. Fe3Sn2 is known to have competing magnetic exchange interactions, correlated electron behavior, weak magnetocrystalline anisotropy, and lattice anisotropy; all of these features are thought to play a role in stabilizing skyrmions in centrosymmetric systems. Our results reveal that at elevated temperatures, there is an absence of magnetocrystalline anisotropy and that the system behaves as a typical exchange ferromagnet with a spin stiffness .