Characterizing anisotropy and uniaxial stress with zero group velocity Lamb modes
Explore the source record for details and available documents.
Engineering - Mechanical and civil engineering, Ma↗
SEARCH · Search NASA
Results for “Mechanical Anisotropy”
Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.
Self-Assembly Interactions in Magnetite-Coated Cellulose Nanocrystals: Implications for Magnetic Hyperthermia Applications
Magnetic cellulose nanocrystal (MCNC) nanocomposites are promising sustainable and biocompatible platforms for magnetic hyperthermia; however, the molecular mechanisms governing Fe 3 O 4 adsorption and deposition onto CNCs remain poorly understood. Here, sulfated (S-CNC) and TEMPO-oxidized CNCs (T-CNC) were used to prepare nanocomposites at 1:2 and 1:4 CNC:Fe 3 O 4 mass ratios, enabling a systematic evaluation of how surface chemistry and nanoparticle loading dictate interfacial interactions and magneto-colloidal behavior. Bare magnetite nanoparticles were 21 ± 5 nm by TEM but grew to 144 ± 18 in the DLS measurement at pH 7. The S-CNC nanocomposites had hydrodynamic sizes between 144 and 210 nm, not much larger than the 140 nm long CNC rods, suggesting an enhanced dispersion stability compared to Fe3O4 alone. X-ray photoelectron spectroscopy combined with density functional theory revealed that −OH and −COOH groups drive electrostatic adsorption with charge transfer from Fe 3 O 4 to the CNC surface, while T-CNCs showed more favorable adsorption energies and evidence of covalent Fe−O bonding. Vibrating sample magnetometry demonstrated superparamagnetic behavior for all samples, with S-CNC/Fe 3 O 4 1:4 and 1:2 displaying saturation magnetizations of 78 and 77 emu/g-Fe 3 O 4 , close to the 83 emu/g of bare magnetite. The T-CNC composites showed lower (60 and 66 emu/g-Fe3O4) saturation magnetizations. Zero-field-cooled/field-cooled measurements resulted in a blocking temperature of 112 K for all samples, except T-CNC/Fe 3 O 4 1:2 (100 K). Magnetic hyperthermia studies revealed that specific absorption rate (SAR) increased with field strength and Fe 3 O 4 content; however, S-CNC/Fe 3 O 4 (1:2) achieved the highest intrinsic SAR per gram of Fe 3 O 4 (649 W/g-Fe 3 O 4 ) likely due to its anisotropy and fast magnetic relaxation. Cytotoxicity assays confirmed that all nanocomposites were nontoxic toward mammalian cells. These results establish quantitative structure−property relationships between CNC surface chemistry, interfacial bonding mechanisms, and magnetic heating performance, providing a foundation for rational design of biocompatible magnetic nanocomposites for hyperthermia and related applications.
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
Universal spin dynamics in infinite-temperature one-dimensional quantum magnets
Here, we address the nature of spin dynamics in various integrable and non-integrable, isotropic and anisotropic quantum spin-$S$ chains, beyond the paradigmatic $S=1/2$ Heisenberg model. In particular, we investigate the algebraic long-time decay $\propto t^{-1/z}$ of the spin-spin correlation function at infinite temperature, using state-of-the-art simulations based on tensor network methods. We identify three universal regimes for the spin transport, independent of the exact microscopic model: (i) superdiffusive with $z=3/2$, as in the Kardar-Parisi-Zhang universality class, when the model is integrable with extra symmetries such as spin isotropy that drive the Drude weight to zero, (ii) ballistic with $z=1$ when the model is integrable with a finite Drude weight, and (iii) diffusive with $z=2$ with easy-axis anisotropy or without integrability, at variance with previous observations.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Ultra–fast, selective, non–melting, laser sintering of alumina with anisotropic and size–suppressed grains
In this paper, we report an ultra-fast sintering phenomenon of alumina achieved by the scanning laser irradiation method. Using CO 2 laser irradiation, we found that micrometer-sized alumina powder (d 50 = 1.2 µm) can be sintered close to full density within a few tens of seconds. The microstructure of laser-sintered alumina was different from that of the furnace-sintered alumina. The relative density and grain size of the laser-sintered alumina gradually decreased from the center of the laser beam to the edge. Anisotropy of the grain size was measured along and perpendicular to the scanning direction. This anisotropy decreased as the scanning speed decreased from 0.1 mm/s to 0.01 mm/s. The sintering master curve of grain size versus relative density, which reflects the sintering mechanism, was found to be affected by the laser scanning speed. When the laser scanning speed was 0.1 mm/s, grain size suppression was found for the almost fully dense alumina. However, at lower scanning speed (e.g., 0.01 mm/s), there was significant grain growth in the regions where the relative density was greater than 90%. Furthermore, these results clearly indicate that alumina can be sintered, in the solid-state, to a high density in a short time using scanning laser and the microstructure is different from the furnace-sintered alumina.
08 HYDROGEN↗
Partial charge transfer and absence of induced magnetization in EuS(111)/Bi 2 Se 3 heterostructures
We report that heterostructures made from topological and magnetic insulators promise to form excellent platforms for new electronic and spintronic functionalities mediated by interfacial effects. We report the results of a first-principles density functional theory study of the geometric, electronic structure, and magnetic properties of the EuS( 111 )/Bi 2 Se 3 interface, including van der Waals and relativistic spin-orbit effects. In contrast to previous theoretical studies, we find no appreciable magnetic anisotropy in such a heterostructure. We also do not see additional induced magnetization at the interface or the magnetic proximity effect on the topological states. This is due to the localized nature of Eu moments and because of a partial charge transfer of ~ 0.5 electron from Eu to Se. The formation of the surface dipole shifts the Dirac cone about 0.4 eV below the chemical potential, and the associated electrostatic screening moves the topological state from the first to the second quintuple layer of Bi 2 Se 3 .
36 MATERIALS SCIENCE↗
Insights into elevated temperature tensile deformation mechanisms and kink banding in additively manufactured tungsten
Additive manufacturing (AM) potentially enables fabrication and repair of plasma facing components (PFCs) of tungsten. However, deformation mechanisms in AM-fabricated tungsten under service-relevant thermomechanical conditions remain unknown majorly due to challenges in achieving crack-free W. This study reveals the deformation mechanisms operative under tension at 800 °C and 1200 °C in the electron beam melting powder bed fusion (EBM-PBF) fabricated W. Textured columnar grains with mixed <001 >/<111 >|| build-direction were observed. Strong anisotropy in tensile properties persisted across test temperatures, and all specimens exhibited extensive deformation-induced banding phenomena. Grain boundary character analysis of the deformed specimens indicated that these deformation bands were kink bands with tilt grain boundaries prominently present at the band-matrix interface. Interestingly, the material within the kink bands rotated toward higher resolved shear stress, providing insights into the origins of kink band formation in body-centered cubic refractory metals. Intragranular misorientation axis analysis revealed that plasticity was dominated by {110} <111 > slip at 800 °C, whereas additional (213)[11̄1] and (112)[11̄1] slip systems activated at 1200 °C. A dense low-angle boundary networks observed near fractured surface indicated the onset of dynamic recrystallization. Results reveal plasticity governing mechanisms in AM-fabricated W under power plant-relevant conditions, and provide insights into kink band attributes in refractory metals.
Mayes, Riley [ORNL] (ORCID:000900089307010X)↗
Diverse magnetic phase diagram and anomalous Hall effect in antiferromagnetic LuMn 6 Sn 6
The interactions between conduction electrons and magnetism can significantly enhance the Hall signal, a phenomenon known as the anomalous Hall effect (AHE). While the AHE is generally not expected in antiferromagnets, a large AHE is observed in certain antiferromagnets with noncollinear spin textures and nonvanishing Berry curvature. In this work, we present a rich temperature and magnetic phase diagram with eight distinct magnetic phases for the antiferromagnetic kagome compound LuMn 6 Sn 6 . The Hall effect analysis in LuMn 6 Sn 6 reveals both intriguing physical phenomena and methodological challenges. In the coplanar canted antiferromagnetic phase, we observe an AHE, which likely originates from the intrinsic effects. At low temperatures, upon entering the ferromagnetic phase, the AHE sharply increases and exceeds the conventional limits expected from intrinsic mechanisms. We also demonstrate the limitations of standard experimental methods in extracting the topological contribution to the Hall effect data. In particular, we show that accounting for magnetoresistance anisotropy helps reduce spurious contribution that can mimic topological Hall signals, although it does not fully resolve it. Furthermore, these shortcomings in current approaches in partitioning the Hall response necessitate new tools to interpret transport results in complex magnetic materials such as LuMn 6 Sn 6 .
Anomalous Hall effect↗
Direct observation of the magnetic anisotropy of an Fe(II) spin crossover molecular thin film
Abstract In this work, we provide clear evidence of magnetic anisotropy in the local orbital moment of a molecular thin film based on the SCO complex [Fe(H 2 B(pz) 2 ) 2 (bipy)] (pz = pyrazol−1−yl, bipy = 2,2′−bipyridine). Field dependent x-ray magnetic circular dichroism measurements indicate that the magnetic easy axis for the orbital moment is along the surface normal direction. Along with the presence of a critical field, our observation points to the existence of an anisotropic energy barrier in the high-spin state. The estimated nonzero coupling constant of ∼2.47 × 10 −5 eV molecule −1 indicates that the observed magnetocrystalline anisotropy is mostly due to spin–orbit coupling. The spin- and orbital-component anisotropies are determined to be 30.9 and 5.04 meV molecule −1 , respectively. Furthermore, the estimated g factor in the range of 2.2–2.45 is consistent with the expected values. This work has paved the way for an understanding of the spin-state-switching mechanism in the presence of magnetic perturbations.
74 ATOMIC AND MOLECULAR PHYSICS↗
Slow magnetic relaxation in a europium(II) complex
Single-ion anisotropy is vital for the observation of Single-Molecule Magnet (SMM) properties (i.e., a slow dynamics of the magnetization) in lanthanide-based systems. In the case of europium, the occurrence of this phenomenon has been inhibited by the spin and orbital quantum numbers that give way to J = 0 in the trivalent state and the half-filled population of the 4f orbitals in the divalent state. Herein, by optimizing the local crystal field of a quasi-linear bis(silylamido) Eu II complex, the [Eu II (N{SiMePh 2 } 2 ) 2 ] SMM is described, providing an example of a europium complex exhibiting slow relaxation of its magnetization. This behavior is dominated by a thermally activated (Orbach-like) mechanism, with an effective energy barrier of approximately 8 K, determined by bulk magnetometry and electron paramagnetic resonance. Ab initio calculations confirm second-order spin-orbit coupling effects lead to non-negligible axial magnetic anisotropy, splitting the ground state multiplet into four Kramers doublets, thereby allowing for the observation of an Orbach-like relaxation at low temperatures.
36 MATERIALS SCIENCE↗
Resonances of electromagnetically induced transparency and absorption in a light field of elliptically polarised waves
Electromagnetically induced transparency (EIT) and electromagnetically induced absorption (EIA) resonances excited by a strong two-frequency field are considered for various values of the total angular momenta of the ground (F{sub g}) and excited (F{sub e}) states at a degenerated optical closed transition F{sub g} → F{sub e}. The light field is formed by two co-propagating waves with arbitrary elliptical polarisations. The process of spontaneous transfer of anisotropy from the excited state to the ground state is shown to determine the formation of the EIA resonance at the transition F{sub g} = F → F{sub e} = F + 1. The results obtained generalise the classification of transitions into ‘bright’ (F{sub g} = F → F{sub e} = F + 1) and ‘dark’ (F{sub g} = F → F{sub e} = F and F{sub g} = F → F{sub e} = F – 1) transitions with respect to the direction of a subnatural resonance. (paper)
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Deconstruction of the Anisotropic Magnetic Interactions from Spin‐Entangled Optical Excitations in van der Waals Antiferromagnets
Magneto-optical excitations in antiferromagnetic d systems can originate from a multiplicity of light-spin and spin-spin interactions, as the light and spin degrees of freedom can be entangled. This is exemplified in van der Waals systems with attendant strong anisotropy between in-plane and out-of-plane directions, such as MnPS 3 and NiPS 3 films studied here. The rich interplay between the magnetic ordering and sub-bandgap optical transitions poses a challenge to resolve the mechanisms driving spin-entangled optical transitions, as well as the single-particle bandgap itself. Here, a high-fidelity ab initio theory is applied to find a realistic estimation of the bandgap by elucidating the atom- and orbital-resolved contributions to the fundamental sub-bands. It is further demonstrated that the spin-entangled excitations, observable as photoluminescence and absorption resonances, originate from an on-site spin-flip transition confined to a magnetic atom (Mn or Ni). The evolution of the spin-flip transition in a magnetic field is used to deduce the effective exchange coupling and anisotropy constants.
2D materials↗
Luminescent and Magnetic Tb-MOF Flakes Deposited on Silicon
The synthesis of a terbium-based 2D metal–organic framework (MOF), of formula [Tb(MeCOO)(PhCOO) 2 ] (1), a crystalline material formed by neutral nanosheets held together by Van der Waals interactions, is presented. The material can be easily exfoliated by sonication and deposited onto different substrates. Uniform distributions of Tb-2D MOF flakes onto silicon were obtained by spin-coating. We report the luminescent and magnetic properties of the deposited flakes compared with those of the bulk. Complex 1 is luminescent in the visible and has a sizeable quantum yield of QY = 61% upon excitation at 280 nm. Photoluminescence measurements performed using a micro-Raman set up allowed us to characterize the luminescent spectra of individual flakes on silicon. Magnetization measurements of flakes-on-silicon with the applied magnetic field in-plane and out-of-plane display anisotropy. Ac susceptibility measurements show that 1 in bulk exhibits field-induced slow relaxation of the magnetization through two relaxation paths and the slowest one, with a relaxation time of τ lf ≈ 0.5 s, is assigned to a direct process mechanism. The reported exfoliation of lanthanide 2D-MOFs onto substrates is an attractive approach for the development of multifunctional materials and devices for different applications.
2D MOFs↗
Magnetic excitations of the hybrid multiferroic (ND 4 ) 2 FeCl 5 ·D 2 O
We report a comprehensive inelastic neutron scattering study of the hybrid molecule-based multiferroic compound ( ND 4 ) 2 FeCl 5 · D 2 O in the zero-field incommensurate cycloidal phase and the high-field quasicollinear phase. The spontaneous electric polarization changes its direction concurrently with the field-induced magnetic transition, from mostly aligned with the crystallographic a axis to the c axis. To account for such a change in polarization direction, the underlying multiferroic mechanism was proposed to switch from the spin-current model induced via the inverse Dzyaloshinskii-Moriya interaction to the p - d hybridization model. We perform a detailed analysis of the inelastic neutron data of ( ND 4 ) 2 FeCl 5 · D 2 O using linear spin-wave theory to quantify magnetic interaction strengths and investigate the possible impact of different multiferroic mechanisms on the magnetic couplings. Overall our result reveals that the spin dynamics of both multiferroic phases can be well described by a Heisenberg Hamiltonian with easy-plane anisotropy. We do not find notable differences between the optimal model parameters of the two phases. The hierarchy of exchange couplings and the balance among frustrated interactions remain the same between two phases, suggesting that magnetic interactions in ( ND 4 ) 2 FeCl 5 · D 2 O are much more robust than the electric polarization in response to delicate reorganizations of the electronic degrees of freedom in an applied magnetic field.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Spin-polarization anisotropy controlled by bending in tungsten diselenide nanoribbons and tunable excitonic states
A WSe 2 monolayer shows many interesting properties due to its spin-orbit coupling induced spin splitting in bands around the Fermi level and the spin-valley configuration. The orientation of the spin polarization in the relevant bands is crucial for the nature of exciton states and the optical valley selectivity. In this work, we studied the WSe 2 nanoribbons under different mechanical bending curvatures and electron/hole doping with density functional theory and their optical absorption and excitonic states with many-body perturbation GW and BSE (Bethe-Salpeter equation) methods. We found that the WSe 2 nanoribbons can exhibit an enhanced SOC effect and a spatially varying spin polarization in bands around the Fermi level under bending. The spin-polarization can show an anisotropy (or asymmetry) in those nearly degenerate bands, leading to a controllable magnetism via bending and electron/hole doping to the nanoribbons, suggesting a potential application in compact and controllable magnetic nanodevices and spintronics. The optical absorption spectrum of the nanoribbon presents a large tunability with bending within the near infrared region of about 0.4 to 1.5 eV, showing an enhanced absorption at a large bending condition. Finally, the exciton states generally show mixed or various spin configuration in the electron and hole pairs that are controlled by bending, potentially useful for applications in spin-based quantum information processes.
36 MATERIALS SCIENCE↗
Enhanced optoelectronic and elastic responses in fluorinated penta-BCN
We report surface passivation in two-dimensional (2D) materials is one of the best approaches to modulate the structural, dynamical, and mechanical stabilities thereby enhancing chemical and physical properties for optoelectronic applications. Here, we report an ab-initio investigation on structurally, thermally, dynamically, and mechanically stable, and experimentally feasible fluorinated penta-BCN (F-BCN) monolayer. The structural reconstruction after fluorination, increases bond lengths and thickness to reduce the average stiffness and elasticity attaining the mechanical isotropy. Nevertheless, the value of 2D Young’s modulus of F-BCN is comparable to the pristine structure at 6% of compression without mechanical instability. A significant bandgap tailoring is achieved, similar to that of mechanical sensitivity, due to applied strain. Remarkably, following the fluorine passivation, the monolayer’s induced wide direct bandgap semiconducting behavior improves optical absorbance and reflectivity, decreases energy loss, changes optical anisotropy, and makes it a promising candidate material for optoelectronic and nanomechanical applications.
36 MATERIALS SCIENCE↗
Decoding the formation of hammerhead ion populations observed by Parker Solar Probe
Context. In situ observations by the Parker Solar Probe (PSP) have revealed new properties of the proton velocity distributions (VDs), including hammerhead features that suggest a non-isotropic broadening of the beams. Aims. The present work proposes a very plausible explanation for the formation of hammerhead proton populations through the action of a proton firehose-like instability triggered by the proton beam. Methods. We investigated a self-generated firehose-like instability driven by the relative drift of ion populations using a simplified moment-based quasi-linear (QL) theory. While simpler and faster than advanced numerical simulations, this toy model provided rapid insights and concisely highlighted the role of plasma micro-instabilities in relaxing the observed anisotropies of particle VDs in the solar wind and space plasmas. Results. The QL theory proposed here shows that the resulting transverse waves are right-hand polarized and have two consequences on the protons: (i) They reduce the relative drift between the beam and the core, but above all, (ii) they induce a strong perpendicular temperature anisotropy specific to the observed hammerhead ion beam. Moreover, the long-run QL results suggest that these hammerhead distributions are rather transitory states that are still subject to relaxation mechanisms, in which instabilities such as the one discussed here are very likely involved. This foundational work motivates future detailed studies using advanced methods.
Shaaban, Shaaban M. (ORCID:000000030465598X)↗
Modeling brittle fracture due to anisotropic thermal expansion in polycrystalline materials
Here, this work investigated brittle fracture of polycrystalline materials due to thermal stresses arising from anisotropic thermal expansion. We used phase-field fracture simulations with the properties of alpha-uranium (α-U) and assumed a linear elastic mechanical response. Three-dimensional simulations were used to predict fracture for various conditions and crystallographic textures. We found that fracture was more pronounced during cooling than during heating because the anisotropy increased with temperature. We also found that the total crack surface area increased with increasing average misorientation, while the net shape change of the material decreased with increasing misorientation. Two-dimensional simulations in which one crystallographic coefficient of thermal expansion (CTE) was set to zero indicated that the expansion behavior in the crystallographic direction with the smallest CTE was the primary cause of fracture.
11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
The orbital effect on the anomalous magnetism and evolution in La $x$ Y 1-$x$ VO 3 (0 ≤ $x$ ≤ 0.2) single crystals
The orbital effect on the anomalous magnetism and evolution of single crystals with low La doping, La $x$ Y 1-$x$ VO 3 ($x$ = 0, 0.1, and 0.2), has been studied using single-crystal X-ray diffraction, specific heat, magnetization, and Raman-scattering techniques. It is found that substituting Y 3+ by La 3+ increases the degeneracy of the $yz/zx$ orbitals and decreases the Jahn-Teller distortion. These weakens the G-type (antiphase ordering along the c axis) orbital ordering phase. Meanwhile, the substituting decreases the magnetism entropy, indicating the shrinking of the t 2g and e g orbital hybridization, eventually destabilizing the C-type (in-phase ordering along the c axis) antiferromagnetic ordering phase. In addition, the mechanism for the shrinking of the diamagnetism with increasing $x$ is analyzed. In conclusion, it may attribute to the competition between the antisymmetric Dzyaloshinsky–Moriya interaction and the single-ion anisotropy.
36 MATERIALS SCIENCE↗