Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “MAGNETIC MATERIALS”

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 1,747 records · Page 97
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Temperature evolution of the phonon dynamics in the Kitaev spin liquid

In this work, we present a study of the phonon dynamics in the honeycomb Kitaev spin model at finite temperatures. We show that the fractionalized spin excitations of the Kitaev spin liquid, the itinerant Majorana fermions, and static Z 2 fluxes have distinct effects on the phonon dynamics, which makes the phonon dynamics a promising tool for exploring the Kitaev spin liquid candidate materials. In particular, we focus on the signature of the fractionalized excitations in the thermodynamic behavior of the sound attenuation and the phonon Hall viscosity: the former describes the phonon decay into the fractionalized excitations, and the latter is the leading order time-reversal symmetry breaking effect on the acoustic phonon. We find that the angular dependence of the attenuation coefficient and its magnitude is modified by the thermal excitation of the Z 2 fluxes. The strength of this effect strongly depends on the relative magnitude of the sound velocity and the Fermi velocity characterizing the low-energy Majorana fermions. We also show that the Hall viscosity is strongly suppressed by the increase of the density of the Z 2 fluxes at finite temperatures. All these observations reflect the effects of the emergent disorder on the Majorana fermions introduced by the Z 2 fluxes. Our analysis is based on the complementary analytical calculations in the low-temperature zero-flux sector, and numerical calculations in the inhomogeneous flux sectors at intermediate and high temperatures with stratified Monte Carlo (strMC) method.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Singly occupied 4⁢𝑓 antiferromagnetic insulators: CePO 4 and CeVO 4

Rare-earth containing wide band gap oxides, which provide spin-photon interface and narrow linewidth optical emission, are getting significant attention as the most promising candidate materials in advancing quantum transduction and memories. Here, in this work, from ab initio calculations, we identify antiferromagnetic ground states in structurally preferred monoclinic CePO 4 and tetragonal CeVO 4 exhibiting localized occupied and unoccupied Ce 4⁢𝑓 states with 4⁢𝑓−4⁢𝑓 transition characteristics. Interestingly, in CePO 4 , O 2⁢𝑝 and P 3⁢𝑝 states hybridize negligibly with Ce 4⁢𝑓 states, while in CeVO 4 , V 3⁢𝑑 and O 2⁢𝑝 states hybridize and appear as extended states in between the occupied and unoccupied Ce 4⁢𝑓 states. Here, phonon calculations and analysis identify and differentiate Raman active phonon modes along with the spin phonon coupling of Ce in both CePO 4 and CeVO 4 that ultimately lead to different 4⁢𝑓 ground-state crystal-field multiplets, which are critical to accurately describe electronic transitions for foundational quantum transduction and memories. Further, the identified 𝐶 1 site symmetry of Ce, lacking inversion symmetry in CePO 4 , is relevant for quantum memories and 𝐷 2⁢𝑑 site symmetry of Ce exhibiting inversion symmetry in CeVO 4 is relevant for quantum transduction.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Understanding the Reactions Between Fe and Se Binary Diffusion Couples

Spurred by recent discoveries of high-temperature superconductivity in Fe-Se based materials, the magnetic, electronic, and catalytic properties of iron-chalcogenides have drawn significant attention. Furthermore, much remains to be understood about the sequence of phase formation in these systems. In this work, we shed light on this issue by preparing a series of binary Fe-Se ultrathin diffusion couples via designed thin film precursors and investigating their structural evolution as a function of composition and annealing temperature. Two previously unreported Fe-Se phases crystallized during the deposition process on a nominally room-temperature Si substrate in the 27-33% and 37-47% Fe (atomic percent) composition regimes. Both phases completely decompose after annealing to 200°C in a nitrogen glovebox. At higher temperatures, the sequence of phase formation is governed by Se loss in the annealing process, consistent with what would be expected from the phase diagram. Films rich in Fe (53-59% Fe) crystalized during deposition as β-FeSe (P4/nmm) with preferred c-axis orientation to the amorphous SiO 2 substrate surface, providing a means to non-epitaxial self-assembly of crystallographically aligned, iron-rich β-FeSe for future research. Our findings suggest the crystallization of binary Fe-Se compounds at room temperature via near diffusionless transformations should be a significant consideration in future attempts to prepare metastable ternary and higher order compounds containing Fe and Se.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Synthesis, Structure, and Properties of the Complex Zintl Phase Eu 9 Zn 4.5 As 9 : A Candidate Topological Insulator and Thermoelectric Material

Reported are the synthesis and detailed analysis of the crystal and electronic structure of the novel Zintl phase Eu 9 Zn 4.5 As 9 . This material was identified in the densely populated Eu–Zn–As compositional space. For structure determination and for property measurements, suitable single crystals of this compound were grown from either Sn- or Pb-flux. Single-crystal X-ray diffraction methods indicate that Eu 9 Zn 4.5 As 9 crystallizes in the orthorhombic crystal system with the space group Pnma (a = 12.1953(7) Å, b = 4.3730(2) Å, c = 42.674(2) Å) and is formally isostructural to Ca 9 Mn 4+x Sb 9 , the less common “9–4–9” type. The structure is heavily disordered, with multiple partially occupied sites, yet, according to the Zintl-Klemm formalism, a charge-balanced composition (Eu 2+ ) 9 (Zn 2+ ) 4.5 (As 3− ) 9 is attained. Electronic structure calculations for a model, disorder-free structure indicate no energy gap between the valence and the conduction bands and suggest (semi)metallic behavior. Preliminary susceptibility measurements confirm the expected divalent nature of Eu 2+ ([Xe] 4 f 7 ground state).

Zintl phases↗
DOE OSTI2026

Disorder-induced magnetoelastic behaviors of MnTexSbyBi1-x-y alloys

This dataset contains input and output files from density functional theory (DFT) simulations used to study the disorder-induced magnetoelastic behaviors of MnTexSbyBi1-x-y (0 ≤ x + y ≤ 1) alloys and their binary end members MnTe, MnSb, and MnBi. The alloys adopt the hexagonal NiAs-type (nickeline) structure and span ternary (MnTexSb1-x, MnTexBi1-x, MnBixSb1-x), and quaternary compositions across the full MnTe–MnSb–MnBi composition triangle. For each alloy composition, the dataset provides DFT calculations in three magnetic configurations: A-type antiferromagnetic (AFM), C-type AFM, and ferromagnetic (FM). Every magnetic configuration folder contains the fully relaxed crystal structure (CONTCAR), VASP input parameters (INCAR), and the main VASP output file (OUTCAR), from which total electronic energies, Mn magnetic moments, lattice parameters, and percent volume changes between magnetic states are extracted. These data are used to construct compositional phase diagrams, evaluate thermodynamic stability (formability), and map magnetoelastic responses across the alloy space. For A-type AFM and FM configurations, additional data are provided as follows: (i) FORCE_CONSTANTS and thermal_properties.yaml files at the top level of A-type_AFM/ and FM/ folders — present only for compositions marked with an asterisk (*) in Table I of the main text. These are derived from Phonopy finite-displacement calculations on full disordered 128-atom supercells and provide vibrational free energy, entropy (Svib)contribution from explicit disorder calculations. (Table I of the associated main manuscript) (ii) A VCA/ subfolder within A-type_AFM/ and FM/, containing FORCE_CONSTANTS and thermal_properties.yaml from Virtual Crystal Approximation phonon calculations (without spin-orbit coupling). VCA data are available for all compositions and are used to estimate vibrational contributions to the Gibbs free energy across the full composition space. (iii) A SOC/ subfolder containing CONTCAR, INCAR, and OUTCAR from spin-orbit coupling calculations, providing relativistic corrections to electronic energies and lattice parameters (Tables S2–S3 of the SM, and Table I of the main manuscript). (iv) A SOC/VCA/ subfolder containing FORCE_CONSTANTS and thermal_properties.yaml from VCA phonon calculations performed within the SOC framework, combining relativistic and vibrational thermodynamic corrections. The computed properties are used to map the AFM–FM magnetic crossover near MnTe0.75Sb0.25, demonstrate disorder- and spin-induced phonon broadening, identify a semiconductor-to-metal crossover, and quantify the pronounced magnetoelastic volume response near the magnetic phase boundary.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Prepare Ground States of Highly Frustrated Magnetic Clusters on Quantum Computers

Solving challenging problems in physical, chemical, and materials sciences is one of the most promising applications of quantum utility that can be realized on current noisy hardware, considering (i) the direct map (encoding) from the quantum particles and their interactions to the qubits and their entangling gates and (ii) the rapidly improved quantum hardware and advanced error-mitigation techniques. Understanding quantum spin liquid in frustrated magnetic materials is a longstanding challenge in condensed matter physics and the nature of the ground-state phases is highly debated among researchers. Using IBM quantum computers with superconducting qubits, we implemented a variational quantum eigensolver (VQE) algorithm to prepare the ground states of two 12-site cluster approximations of these highly frustrated magnetic materials. The interaction graphs of the two corresponding Hamiltonians are (a) the six-pointed star graph (a unit cell of the kagome lattice) and (b) the cuboctahedral graph (the kagome on a sphere). These are also two instances of Quantum Max Cut problem. With the VQE based on the Hamiltonian variational ansatz acting on a valence bond solid initial trial state, we prepared the ground states and obtained the exact ground energy on simulator and high accuracy on noisy hardware. The deep ansatz necessary to reach the ground state of the cuboctahedral graph indicates that it is a hard instance of Quantum Max Cut.

Wang, Yan↗
DOE OSTI2015

Magnetic Correlations in the Quasi-Two-Dimensional Semiconducting Ferromagnet CrSiTe 3

Intrinsic, 2D ferromagnetic semiconductors are an important class of materials for overcoming dilute magnetic semiconductors’ limitations for spintronics. CrSiTe 3 is a particularly interesting material of this class, since it can likely be exfoliated to single layers, for which T c is predicted to increase dramatically. Establishing the nature of the bulk material’s magnetism is necessary for understanding the thin-film magnetic behavior and the material’s possible applications. In this work, we use elastic and inelastic neutron scattering to measure the magnetic properties of single crystalline CrSiTe 3 . We find a very small single ion anisotropy that favors magnetic ordering along the c-axis and that the measured spin waves fit well to a model in which the moments are only weakly coupled along that direction. Then, we find that both static and dynamic correlations persist within the ab-plane up to at least 300 K, which is strong evidence of the material's 2D characteristics that are relevant for future studies on thin film and monolayer samples.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

Iron-Nickel-Based SuperMagnets: Multiscale Development of L10 Materials for Rare Earth-Free Permanent Magnets

REACT Project: Northeastern University will develop bulk quantities of rare-earth-free permanent magnets with an iron-nickel crystal structure for use in the electric motors of renewable power generators and EVs. These materials could offer magnetic properties that are equivalent to today’s best commercial magnets, but with a significant cost reduction and diminished environmental impact. This iron-nickel crystal structure, which is only found naturally in meteorites and developed over billions of years in space, will be artificially synthesized by the Northeastern University team. Its material structure will be replicated with the assistance of alloying elements introduced to help it achieve superior magnetic properties. The ultimate goal of this project is to demonstrate bulk magnetic properties that can be fabricated at the industrial scale.

ARPA-E↗
NASA NTRS1991

Magnetic field effects on microwave absorbing materials

The objective of this program was to gather information to formulate a microwave absorber that can work in the presence of strong constant direct current (DC) magnetic fields. The program was conducted in four steps. The first step was to investigate the electrical and magnetic properties of magnetic and ferrite microwave absorbers in the presence of strong magnetic fields. This included both experimental measurements and a literature survey of properties that may be applicable to finding an appropriate absorbing material. The second step was to identify those material properties that will produce desirable absorptive properties in the presence of intense magnetic fields and determine the range of magnetic field in which the absorbers remain effective. The third step was to establish ferrite absorber designs that will produce low reflection and adequate absorption in the presence of intense inhomogeneous static magnetic fields. The fourth and final step was to prepare and test samples of such magnetic microwave absorbers if such designs seem practical.

Goldberg, Ira↗
DOE OSTI2020

Modeling of Magnetic Properties of Magnetorheological Elastomers Using JA Hysteresis Model

Magnetorheological elastomers (MREs) are composite materials that consist of magnetically permeable particles in a nonmagnetic polymeric matrix. Under the influence of an external magnetic field, a reversible deformation change occurs in the mechanical properties of these materials. Due to their coupled magnetomechanical response, these materials have been found suitable for a range of applications including tunable vibration absorbers, sensors, and actuators. Notably, improvement of such devices are prerequisites to efficient energy conversion systems, hence the need to understand further the MRE technology. The Jiles-Atherton (JA) theory takes into consideration the magneto-coupling experienced by effective domains in a magnetic material. Algorithm based on the theory yields five model parameters; saturation magnetization (M s ), domain density (a), domain coupling (α), loss coefficient (k), and reversibility (c). Using JA theory, model parameters were calculated and linked to the physical attributes of Fe powder and isotropic MRE. The results show that the calculated Ms for the MRE is reasonably related to that of the Fe powder by a factor of the particle's volume fraction used in the MRE. Further, the calculated k, a, and α provided support for the reduced pinning factor, domain density, and increased domain coupling in the MRE due to the changes in the domain structure between the two materials. From the calculated JA parameters, finite-element modeling (FEM) of the MRE hysteresis loop was performed. The analysis showed that the modeled magnetic properties including coercivity, remanence, and coordinates of the hysteresis loop tip vary with geometric position.

42 ENGINEERING↗
DOE OSTI2018

Adsorption Performance and Mechanisms of Methylene Blue Removal by Non-magnetic and Magnetic Particles Derived from the Vallisneria natans Waste

Vallisneria natans (V. natans) is a submerged aquatic plant, and its dried biomass waste was used to prepare magnetic particle biomass adsorbent by chemical co-precipitation via FeSO{sub 4}·7H{sub 2}O and FeCl{sub 3}·6H{sub 2}O as iron precursors. Brunauer–Emmett–Teller specific surface area, total pore volume, and average pore width were 7.434 m{sup 2} g{sup −1}, 0.013 cm{sup 3} g{sup −1}, and 6.992 nm for magnetic V. natans, correspondingly, and 3.575 m{sup 2} g{sup −1}, 0.004 cm{sup 3} g{sup −1}, and 4.476 nm for non-magnetic V. natans, respectively. The adsorption kinetics of methylene blue (MB) is a more appropriate fit for pseudo-second-order kinetic model than pseudo-first-order and intraparticle diffusion kinetic models. Isotherm results showed that the adsorption of MB onto the non-magnetic and magnetic adsorbents agrees well with Dubinin–Radushkevich isotherm model. Moreover, the thermodynamics study implied that the adsorption of MB onto both adsorbents is a spontaneous and exothermic process. The maximum adsorption capacities of MB on non-magnetic and magnetic V. natans were 657.90 and 473.93 mg g{sup −1} at 303 K, correspondingly.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Preparation of Fine Single Crystals of Rutheno-Cuprates by the Self-Flux Method with Alumina Boats

We investigate the single crystal growth of rutheno-cuprates, which are known to be magnetic superconductors. We attempted the single crystal growth of two systems, RuSr{sub 2}GdCu{sub 2}O{sub 8−δ} (RuGd-1212) and RuSr{sub 2}(Gd,Ce){sub 2}Cu{sub 2}O{sub 10−δ} (RuGd-1222), by the self-flux method with alumina boats. Fine cubic crystals of RuGd-1212 with a side length of approximately 5 μ m were obtained by slow cooling from 1350 to 940 {sup ∘}C. Plate-like RuGd-1222 crystals with a smooth plane were obtained at the surface of the precursor pellet. RuGd-1222 was more stable at high temperatures than RuGd-1212 and was also superconductive, but its superconductivity weakened as the cooling rate decreased. This weakening was induced by decomposition. Therefore, high-quality RuGd-1222 single crystals were difficult to obtain, and we failed to extract only the smooth planar crystal part. As a modified synthesis technique, we mixed a precursor containing Ru–Sr–Gd–Ce flux with RuGd-1222 powders and gradually cooled the mixture from 1350 to 1090 {sup ∘}C. A plate-like RuGd-1222 sample with a smooth surface and a size of 70 × 30μm{sup 2} was obtained from the side surface of the precursor pellet. By this technique, we could separate the planar crystal part. Semiquantitative composition analysis confirmed this planar crystal as a RuGd-1222 phase. The X-ray diffraction peak suggested the (0014) plane, implying that the plate-like precipitates are c-axis-oriented RuGd-1222 single crystals.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Wave-Vector Filtering Effect in a Novel Magnetic Nanostructure with Zero Average Magnetic Field

We report a theoretical investigation on wave-vector filtering (WVF) effect in a magnetic nanostructure, which can be experimentally realized by depositing ferromagnetic (FM) stripes on the surface of GaAs/Al{sub x}Ga{sub 1-x}As heterostructure. An appreciable WVF effect appears in this nanosystem. The WVF efficiency is associated with structural parameters of magnetic nanostructure. Therefore, such a device can be employed as a momentum filter for nanoelectronics device applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Magnetic and Magnetotransport Characteristics of Cr-Substituted Ni{sub 55}Mn{sub 34}Sn{sub 11} Thin Films Grown by Magnetron Sputtering

Highly oriented Cr-substituted Ni{sub 55}Mn{sub 34}Sn{sub 11} Heusler thin films having thickness ~ 400 nm were deposited by Ultrahigh vacuum dc magnetron sputtering on MgO (100) substrates. At room temperature, the films exhibit a mixture of dominant L2{sub 1} cubic austenite phase, as revealed by the intense (002) and (004) peaks, along with small fraction of the orthorhombic–martensitic phase. Surface morphology of the thin films showed distribution of Cr-rich and Cr-deficit regions together with patterned and aligned magnetic domains, thus bringing out the inherent room temperature ferromagnetism of the film. At temperatures above the Curie temperature, T{sub C} ~ 321 K, the magnetic behaviour of the films is seen to follow the Curie law rather than the Curie–Weiss law. Ferromagnetic to antiferromagnetic transition appears at T{sub N} ~ 247 K, which gives rise to exchange bias at low temperatures due to the coexistence of the two magnetic orders. This phase coexistence also leads to the formation of a spin glass state deep into the martensitic region. The film exhibits metal-like nature at high temperature and semiconductor-like behaviour with the lowering of temperature. A reentrant metallic state is observed at T ≤ 38 K during cooling that persists up to ≤ 62 K in warming cycle. The hysteresis in the ρ–T curve spread over a very wide temperature range confirms the magnetic phase coexistence in the martensitic state in the present thin films. The magnetoresistance (MR) first increases (2.4% at 300 K and H = 50 kOe) with temperature and maximizes to around ~ 3.25% at T = 150 K and then starts decreasing. Its value in the glassy state is very small. This shows that a magnetic liquid like state is more conducive to larger MR.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Modification of carbonyl iron particles by carboxyl-containing polydimethylsiloxanes

The possibility of preparing magnetic particles with the “core–shell” structure was demonstrated. The procedure is based on the treatment of carbonyl iron particles with polydimethylsiloxanes (PDMS) containing terminal or distributed over the chain carboxyl groups attached via the alkyl or aryl spacer. The presence of carboxyl-containing PDMS grafted to the surface of carbonyl iron particles was revealed by electron microscopy. Magnetorheological fluids and magnetic elastomers containing magnetic particles with the “core–shell” structure were obtained, and their rheological properties were studied.

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

Microstructural Evolution of Steel During Magnetic Field-Assisted Processing

Advancing magnetic field-assisted processing, as an energy-efficient method for tailoring steel microstructures, requires a thorough understanding of how the high magnetic field impacts microstructural evolution, particularly its effect on prior austenite grain structures. The current investigation of a near-eutectoid composition, Fe-C alloy, uses electron backscatter diffraction to examine the morphology and orientation of martensite and pearlite microstructures, and to reconstruct the parent austenite microstructures present during equivalent heating under varied magnetic field strengths (0-T, 2-T, 5-T, and 9-T). It was observed that the magnetic field has a negligible effect on martensite lath/block width, slightly decreases prior austenite grain size, and increases the fraction of austenite grains with annealing twins. Additionally, the magnetic field increases the phase fraction of proeutectoid ferrite but has a negligible effect on pearlite block size and the distribution of boundary misorientation angles. No preferred texture was induced by the magnetic field, regardless of the applied field direction, in the proeutectoid ferrite phase or the martensite and prior austenite microstructures. Furthermore, the observed results contradict previous literature, and the differences are discussed.

Magnetic Materials↗
DOE OSTI2026

Crystal structure, magnetism, and specific heat of lightly depleted layered honeycomb oxides, Na$_2$(Ni$_{2-x}$D$_x$)TeO$_6$ ($D$ = Mg, Ga, Co; 0.10 ≤ $x$ ≤ 0.25)

Layered oxides, in which transition metal atoms form a honeycomb lattice, are known for complex magnetic phase diagrams. In this work we study the doped compounds, Na$_2$(Ni$_{2-x}$D$_x$)TeO$_6$, $D$ = Mg, Ga, and Co (0.10 ≤ $x$ ≤ 0.25), to understand how chemical dilution at the nickel site influences the stability of magnetic exchanges within the honeycomb layer of the parent, Na$_2$ Ni$_2$ TeO$_6$. Here, the studied compounds were found to crystallize in $P6_3/mcm$ space group common to P2 type layered oxides. In general, the lattice parameters and the unit cell volume expanded with increased doping. The oxidation states determined from X-ray photoelectron spectroscopy were consistent with bond valence sum estimates, that confirmed the presence of Ni$^{2+}$, Mg$^{2+}$, Ga$^{3+}$, Co$^{2+}$ in our samples. Irrespective of magnetic or non-magnetic doping, the magnetic phase transition temperature ($T_N$) of the doped compounds were reduced from that of Na$_2$ Ni$_2$ TeO$_6$ or Na$_2$ Co$_2$ TeO$_6$, and lay between 21.7 K and 26.8 K. The effective paramagnetic moments extracted from Curie–Weiss analysis were in the range 3.17 μ B to 3.84 μ B and the Weiss temperatures were between $-15$ K and $-25$ K, suggesting antiferromagnetism. Mg- and Ga-doped compounds showed free spin formation, indicated by Curie–Weiss tails in their magnetic susceptibility. Our results suggest emergence of short-range magnetic correlations in Na$_2$(Ni$_{2-x}$D$_x$)TeO$_6$, enhanced due to the depletion of the Ni honeycomb lattice.

75 - CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY A↗