Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “antiferromagnet”

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.

At least 1,027 records · Page 57
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Ultrafast Nanoimaging of Spin-Mediated Shear Waves in an Acoustic Cavity

Strong spin–lattice coupling in van der Waals (vdW) magnets shows potential for innovative magneto-mechanical applications. Here, nanoscale and picosecond imaging by ultrafast electron microscopy reveal heterogeneous spin-mediated coherent acoustic phonon dynamics in a thin-film cavity of the vdW antiferromagnet FePS3. The harmonics of the interlayer shear acoustic modes are observed, in which the even and odd harmonics exhibit distinct nanoscopic dynamics. Corroborated by acoustic wave simulation, the role of defects in forming even harmonics is elucidated. Above the Néel temperature (T N ), the interlayer shear acoustic harmonics are suppressed, while the in-plane traveling wave is predominantly excited. The dominant acoustic dynamics shifts from the out-of-plane shear to the in-plane traveling wave across T N , demonstrating that magnetic properties can influence phonon scattering pathways. In conclusion, the spatiotemporally resolved structural characterization provides valuable nanoscopic insights for interlayer-shear-mode-based acoustic cavities, opening up possibilities for magneto-mechanical applications of vdW magnets.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Even–Odd Layer-Dependent Exchange Bias Effect in MnBi 2 Te 4 Chern Insulator Devices

Magnetic topological materials with coexisting magnetism and nontrivial band structures exhibit many novel quantum phenomena, including the quantum anomalous Hall effect, the axion insulator state, and the Weyl semimetal phase. As a stoichiometric layered antiferromagnetic topological insulator, thin films of MnBi 2 Te 4 show fascinating even–odd layer-dependent physics. Here, in this work, we fabricate a series of thin-flake MnBi 2 Te 4 devices using stencil masks and observe the Chern insulator state at high magnetic fields. Upon magnetic field training, a large exchange bias effect is observed in odd but not in even septuple layer (SL) devices. Through theoretical calculations, we attribute the even–odd layer-dependent exchange bias effect to the contrasting surface and bulk magnetic properties of MnBi 2 Te 4 devices. Our findings reveal the microscopic magnetic configuration of MnBi 2 Te 4 thin flakes and highlight the challenges in replicating the zero magnetic field quantum anomalous Hall effect in odd SL MnBi 2 Te 4 devices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Coherent Magnon–Photon Coupling in the Magnetic Semiconductor CrSBr

Magnon-based hybrid quantum systems are promising candidates for quantum interconnects and quantum sensors, and they offer a rich platform for exploring nonlinear magnonics and cavity–photon interactions. Two-dimensional (2D) van der Waals magnets provide a compact, atomically flat geometry that can be easily integrated into existing quantum circuits, such as superconducting resonators and qubits. Among various 2D magnets, the magnetic semiconductor CrSBr is particularly unique due to its strong spin–exciton, spin–lattice, and magnon–exciton interactions. In this work, we demonstrate coherent coupling between antiferromagnetic (AFM) magnons in CrSBr and microwave photons in a niobium-(Nb)-based-on-chip resonator. We tuned the magnon–photon coupling strength by changing the number of CrSBr flakes integrated into the Nb microwave photon resonators. Furthermore, this work demonstrates the first step toward integrating layered van der Waals 2D magnets into superconducting microwave circuits, with full access for microwave and optical probing.

Electromagnetic radiation↗
DOE OSTI2024

Deconvoluting XPS Spectra of La-Containing Perovskites from First-Principles

Perovskite-based oxides are used in electrochemical CO 2 and H 2 O reduction in electrochemical cells due to their compositional versatility, redox properties and stability. However limited knowledge exists on the mechanisms driving these processes. Toward this understanding, herein we probe the core level binding energy shifts of water-derived adspecies (H, O, OH, H 2 O) as well as the adsorption of CO 2 on LaCoO 3 and LaNiO 3 and we correlate the simulated peaks with experimental Temperature Programmed X-ray Photoelectron Spectroscopy (TPXPS) results. We find the strong adsorption of such chemical species can affect the antiferromagnetic ordering of LaNiO 3 . The adsorption of such adspecies is further quantified through Bader and differential charge analyses. We find the higher O 1s core level binding energy peak for both LaCoO 3 and LaNiO 3 corresponds to adsorption of water-related species and CO 2 , while the lower energy peak is due to lattice oxygen. We further correlate these DFT-based core level O 1s binding energies with the TPXPS measurements to quantify the decrease of the O 1s contribution due to desorption of adsorbates and the apparent increase of the lattice oxygen (both bulk and surface) with temperature. Finally, we quantify the influence of adsorbates on the La 4d, Co 2p and the Ni 3p core level binding energy shifts. This work demonstrates how theoretically generated XPS data can be utilized to predict species-specific binding energy shifts to assist in the deconvolution of the experimental results.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Magnetic cations doped into a double perovskite semiconductor

Here we report two solid solutions based on the magnetic ion doping of the double perovskite oxide Sr 2 GaSbO 6 : Sr 2 Ga 1-x Cr x SbO 6 (0.1 ≤ x ≤ 0.4) and Sr 2 Ga 1-x Fe x SbO 6 (0.1 ≤ x ≤ 0.4). All compositions crystallize in the same space group ($I4/m$) as their undoped parent phase Sr 2 GaSbO 6 , with the trivalent magnetic cations Cr 3+ or Fe 3+ partially substituting for non-magnetic Ga 3+ in one of the B-cation sites. The Cr- and Fe-doped phases display dominant antiferromagnetic coupling among the dopant magnetic moments, and exhibit decreasing band gaps with increasing substitution level.

antiferromagnetic coupling↗
DOE OSTI2020

In-situ fabrication and transport properties of (111) Y 2 Ir 2 O 7 epitaxial thin film

We report on the successful fabrication of (111) oriented thin films of pyrochlore iridate Y 2 Ir 2 O 7 by means of solid phase epitaxy. Essentially, we developed an entirely in situ annealing protocol, which is superior to the conventional ex-situ routine that requires multi-hour annealing to stabilize the proper pyrochlore structure. The morphological quality of the films has been confirmed by x-ray diffraction, reflectivity, and reciprocal space mapping, demonstrating their high crystallinity with a pure pyrochlore phase and an expected epitaxial relation to the substrate. Strikingly, below the magnetic phase transition, the temperature dependence of resistivity shows a power-law behavior with the power exponent of similar to 3/2, characteristic of a Weyl semimetal in the presence of impurities and electron-electron correlations. Finally, below 10K, the magneto-transport measurements reveal the emergence of a non-saturated negative magnetoresistance up to 9T with a small "valley" around zero field. These findings are further interpreted in relation to the weak anti-localization effect and the non-collinear antiferromagnetic ordering on the Ir sublattice.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Spin orbit torque switching of synthetic Co/Ir/Co trilayers with perpendicular anisotropy and tunable interlayer coupling

Spin orbit torque (SOT) has attracted much attention as an energy efficient electrical method to switch the magnetization in single magnetic layer with both in-plane and perpendicular anisotropy. Here, we report SOT switching of synthetic antiferromagnetic and ferrimagnetic Co/Ir/Co trilayers, where the net magnetization and the interlayer coupling strength are highly controllable. Here, a weak external field dependence of the SOT switching was observed due to the robust domain wall structure in the trilayer. The switching current density was observed to scale inversely with the net magnetization. For trilayers with the same net magnetization, switching current is independent of the layer order because switching in the thicker Co layer dominates. In both ferromagnetic and antiferromagetic regimes, the switching current reflects the interlayer coupling strength.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2021

Magnetoelastic standing waves induced in UO 2 by microsecond magnetic field pulses

Significance UO 2 is of particular interest due to its use as a nuclear fuel, its unusually poor thermal conductivity, and its uniquely strong magnetoelastic properties characterized by a linear coupling between strain and magnetization. We clearly observe mechanical standing waves and elastic resonances in a single crystal, induced by microsecond magnetic field pulses. The phase and amplitude of the mechanical resonances are modulated by the piezomagnetic switching behavior, offering a sensitive probe for otherwise hard to detect magnetic dynamics in UO 2 . We highlight the importance of magnetic domains in the attenuation of the mechanical resonances and the robustness of the antiferromagnetic state in UO 2 against externally applied magnetic fields to 150 T.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2023

Strong enhancement of magnetic ordering temperature and structural/valence transitions in EuPd 3 S 4 under high pressure

We present a comprehensive study of the inhomogeneous mixed-valence compound, EuPd 3 S 4 , by electrical transport, X-ray diffraction, time-domain 151 Eu synchrotron Mössbauer spectroscopy, and X-ray absorption spectroscopy measurements under high pressure. Electrical transport measurements show that the antiferromagnetic ordering temperature, T N , increases rapidly from 2.8 K at ambient pressure to 23.5 K at ~19 GPa and plateaus between ~19 and ~29 GPa after which no anomaly associated with T N is detected. A pressure-induced first-order structural transition from cubic to tetragonal is observed, with a rather broad coexistence region (~20 GPa to ~30 GPa) that corresponds to the T N plateau. Mössbauer spectroscopy measurements show a clear valence transition from approximately 50:50 Eu 2+ :Eu 3+ to fully Eu 3+ at ~28 GPa, consistent with the vanishing of the magnetic order at the same pressure. X-ray absorption data show a transition to a fully trivalent state at a similar pressure. Our results show that pressure first greatly enhances T N , most likely via enhanced hybridization between the Eu 4 f states and the conduction band, and then, second, causes a structural phase transition that coincides with the conversion of the europium to a fully trivalent state.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Geometric frustration in the myosin superlattice of vertebrate muscle

Geometric frustration results from an incompatibility between minimum energy arrangements and the geometry of a system, and gives rise to interesting and novel phenomena. Here, we report geometric frustration in a native biological macromolecular system---vertebrate muscle. We analyse the disorder in the myosin filament rotations in the myofibrils of vertebrate striated (skeletal and cardiac) muscle, as seen in thin-section electron micrographs, and show that the distribution of rotations corresponds to an archetypical geometrically frustrated system---the triangular Ising antiferromagnet. Spatial correlations are evident out to at least six lattice spacings. The results demonstrate that geometric frustration can drive the development of structure in complex biological systems, and may have implications for the nature of the actin--myosin interactions involved in muscle contraction. Identification of the distribution of myosin filament rotations with an Ising model allows the extensive results on the latter to be applied to this system. It shows how local interactions (between adjacent myosin filaments) can determine long-range order and, conversely, how observations of long-range order (such as patterns seen in electron micrographs) can be used to estimate the energetics of these local interactions. Furthermore, since diffraction by a disordered system is a function of the second-order statistics, the derived correlations allow more accurate diffraction calculations, which can aid in interpretation of X-ray diffraction data from muscle specimens for structural analysis.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

Magnetic devil's staircaselike behavior in quasiperiodic qubit lattices

The devil's staircase (DS) phenomenon is a fractal response of magnetization to external fields, traditionally observed in periodic ferromagnetic systems, where the commensurability between spin arrangements, lattice parameters, and external magnetic fields governs abrupt changes in magnetization. Its occurrence in aperiodic, fractal-type systems has remained largely unexplored, despite their natural compatibility with such phenomena. Using a quantum annealing device, we uncover a wealth of abrupt magnetic transitions between spin manifolds driven by increasing external magnetic fields within a simple yet effective Ising-model framework. In contrast to periodic systems, where DS arises from long-range competing interactions, our findings reveal that short-range, purely antiferromagnetic couplings in aperiodic geometries produce equally rich ground-state magnetization patterns. Here, we demonstrate that while magnetic textures are determined by the lattice size, their formation remains remarkably robust and independent of scale, with commensurability emerging locally. Our results challenge the prevailing view that DS behavior is limited to periodic systems and establish quasiperiodic geometries as a natural host for this phenomenon.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Spin-coupling topology in the copper hexamer compounds A 2 Cu 3 O(SO 4 ) 3 ( A =Na, K)

The compounds A 2 Cu 3 O(SO 4 ) 3 (A=Na,K) are characterized by copper hexamers that are weakly coupled to realize antiferromagnetic order below TN≈3K. They constitute quantum spin systems with S=1 triplet ground states. In this work, we investigated the energy-level splittings of the copper hexamers by inelastic neutron scattering experiments covering the entire range of the magnetic excitation spectra. Additionally, the observed transitions are governed by very unusual selection rules that we ascribe to the underlying spin-coupling topology. This is rationalized by model calculations that allow an unambiguous interpretation of the magnetic excitations concerning both the peak assignments and the nature of the spin-coupling parameters.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Canted Eu magnetic structure in EuMnSb 2

Magnetic ordering breaks the time-reversal symmetry, greatly impacting material topological properties. Here, we report the investigation of the magnetic properties of the layered EuMnSb 2 , which has two sets of magnetic sublattices. Both the magnetization and electrical resistivity reveal two phase transitions with one at T N,Eu ~21K and the other at T N,Mn ~346K. Single crystal neutron diffraction refinement indicates that both transitions are originated from magnetic ordering. Below T N,Mn , the Mn sublattice forms the C-type antiferromagnetic (AFM) structure with moments [(4.5±0.6)μB at 7 K] pointing along the a axis. Below T N,Eu , the Eu sublattice forms the canted A-type AFM structure with moments [(5.9±0.8)μB at 7 K] lying in the ac plane but pointing (41 ± 1)° away from the a axis. Quantitative analysis indicates that the spin-spin correlation length, while anisotropic, has long-range characteristic in all directions for both the Eu and Mn sublattices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Field-induced transitions in the Kitaev material α - RuCl 3 probed by thermal expansion and magnetostriction

High-resolution thermal expansion and magnetostriction measurements were performed on single crystals of α - RuCl 3 in magnetic fields applied parallel to the Ru-Ru bonds. The length changes were measured in the direction perpendicular to the honeycomb planes. Here, our data show clear thermodynamic characteristics for the field-induced phase transition at the critical field μ 0 H c 1 = 7.8 ( 2 ) T where the antiferromagnetic zigzag order is suppressed. At higher fields, a kink in the magnetostriction coefficient signals an additional transition or crossover around μ 0 H c 2 ≈ 11 T . The extracted Grüneisen ratio shows typical hallmarks for quantum criticality near H c 1 but also displays anomalous behavior above H c 1 . We compare our experimental data with spin-wave calculations employing a minimal Kitaev-Heisenberg model in the semiclassical limit. Most of the salient features are in agreement with each other, however, the peculiar features in the region above H c 1 cannot be accounted for in our semiclassical modeling and hence suggest a genuine quantum nature. We construct a phase diagram for α - RuCl 3 in a magnetic field along the Ru-Ru bonds, displaying a zigzag ordered state below H c 1 , a quantum paramagnetic regime between H c 1 and H c 2 , and a semiclassical partially polarized state above H c 2 .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Charge density modulation and defect ordering in the $Na_xMnBi_y$ magnetic semimetal

The I-Mn-V antiferromagnet, NaMnBi, develops a very large positive magnetoresistance (MR) up to 10 000% at 2 K and 9 T in crystals showing a semiconductor-to-metal transition (SMT). In the absence of an SMT, a modest (20%) MR is achieved. Here, we show that upon cooling below the magnetic transition, a spatial modulation appears giving rise to new Bragg peaks due to charge and defect ordering in a checkerboard pattern, with two kinds of modulation vectors, $q_1 = \left( \frac{2}{3}, 0, 1 \right)$ and $q_2 = \left( \frac{2}{3}, \frac{1}{3}, \frac {1}{2} \right)$. This constitutes a superlattice transition ($T_s$) that lowers the symmetry from the high-temperature centrosymmetric $P4/nmm$ to the noncentrosymmetric $P\overline{4}m2$. In crystals with a large MR, a close to room temperature $T_s$ is observed with $q_1$ appearing first, followed by $q_2$. In crystals with low MR, however, $T_s$ is much lower and only $q_1$ is observed. Finally, the charge modulation and spin fluctuations may both contribute to the enhancement of MR.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Ferromagnetic cluster-glass phase in Ca(Co 1-x Ir x ) 2-y As 2 crystals

In this study, single crystals of Ca(Co 1-x Ir x ) 2-y As 2 with 0≤x≤0.35 and 0.10≤y≤0.14 have been grown using the self-flux technique and characterized by single-crystal x-ray diffraction (XRD), energy-dispersive x-ray spectroscopy, magnetization M, and magnetic susceptibility χ measurements versus temperature T, magnetic field H, and time t, and heat-capacity C p (H,T) measurements. The XRD refinements reveal that all the Ir-substituted crystals crystallize in a collapsed-tetragonal structure as does the parent CaCo 2-y As 2 compound. A small 3.3% Ir substitution for Co in CaCo 1.86 As 2 drastically lowers the A-type antiferromagnetic (AFM) transition temperature T N from 52 to 23 K with a significant enhancement of the Sommerfeld electronic heat-capacity coefficient. The A-type AFM structure consists of ab-plane layers of spins ferromagnetically aligned along the c axis with AFM alignment of the spins in adjacent layers along this axis. The positive Weiss temperatures obtained from Curie-Weiss fits to the χ(T>T N ) data indicate that the dominant magnetic interactions are ferromagnetic (FM) for all x. A magnetic phase boundary is inferred to be present between x=0.14 and x=0.17 from a discontinuity in the x dependencies of the effective moment and Weiss temperature in the Curie-Weiss fits. FM fluctuations that strongly increase with increasing x are also revealed from the χ(T) data. Furthermore, the magnetic ground state for x≥0.17 is a spin glass as indicated by hysteresis in χ(T) between field-cooled and zero-field-cooled measurements and from the relaxation of M in a small field that exhibits a stretched-exponential time dependence. The spin glass has a small FM component to the ordering and is hence inferred to be comprised of small FM clusters. The competing AFM and FM interactions along with crystallographic disorder associated with Ir substitution are inferred to be responsible for the development of a FM cluster-glass phase. A logarithmic T dependence of Cp at low T for x=0.14 is consistent with the presence of significant FM quantum fluctuations. This composition is near the T=0 boundary at x≈0.16 between the A-type AFM phase containing ferromagnetically-aligned layers of spins and the FM cluster-glass phase.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Magnetism of Nd 2 O 3 single crystals near the Néel temperature

Single crystals of Nd 2 O 3 were grown and characterized using neutron scattering and thermodynamic measurements. Nd 2 O 3 has long-range antiferromagnetic order below T N =0.55 K and specific-heat measurements have demonstrated that a significant amount of the magnetic entropy is released above T N . Inelastic neutron scattering experiments reveal a magnetic mode(s) with little dispersion peaked at ≈0.37meV that is of greatest intensity below T N but persists above 2T N . This persistence of dynamic correlations is likely related to frustrated interactions associated with the nearly ideal stacked triangular lattice geometry of J eff =12 spins on Nd 3+ ions. Furthermore, the magnetization is observed to be strongly anisotropic at all temperatures due to crystal field effects, with easy-plane anisotropy observed. Additionally, a noncompensated magnetic structure is inferred from the temperature dependence of the magnetization when a magnetic field of sufficient strength is applied within the basal plane near T N , and the evolution of the long-range order is summarized in a temperature-field phase diagram.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗