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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.

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At least 289 records · Page 16
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Decoupling the effects of texture and composition on magnetic properties of Fe-Si sheet processed by shear deformation

Soft magnetic Fe-Si alloys (electrical steels) possess exceptional functional properties such as high permeability, low coercivity, and low core loss, which generally improve with increasing Si content in the alloy. However, Fe-Si alloys containing > 3.5 wt% Si are also characterized by prohibitively low workability and poor ductility that have prevented their efficient commercial production in sheet form by rolling. This has limited their use for improving efficiency of motors and transformers. In this study, hybrid cutting-extrusion (HCE) is used as a single-step thermomechanical processing method to produce continuous Fe-Si alloy sheet with high Si compositions of 4 wt% to 6.5 wt%. HCE sheet is shown to have a homogeneous annealed grain structure and simple-shear crystallographic textures. By controlling the HCE deformation path, varied crystallographic shear textures are created in the sheet. Quasi-static magnetic properties of the HCE sheet are evaluated to decouple the effects of sheet texture and Si composition on resultant permeability and coercivity properties. The results suggest that HCE, with suitable process scaling, is a viable route for production of high-Si content electrical steel sheet for next-generation motors and transformers.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Investigation of Magnetic Properties of Multilayer Thin Films with Spin-Wave Resonance

A theory has been developed to simulate spin-wave resonance (SWR) modes in the multilayer systems consisting of alternate magnetic and nonmagnetic layers. An equation of motion of magnetization with Gilbert-type damping parameter for simulating SWR modes was used. It has been realized that the theory developed for the magnetic multilayer films is suitable to study the spin dynamics and extract various magnetic parameters. It has been shown that SWR modes strongly depend on an effective magnetic anisotropy constant (K{sub eff}), interlayer exchange coupling constant (A{sub 12}) and effective magnetization (M{sub eff}). The nature of the effective magnetic anisotropy and interlayer exchange coupling constants has been investigated by using the developed SWR theory in detail. The separation between optic and acoustic modes strongly depends on the magnitude of the interlayer exchange coupling constant, whereas the relative position of the acoustic and optic modes depends on the sign of A{sub 12}. With increasing the interlayer exchange coupling constant, the resonance field of the optic mode decreases (increases) for ferromagnetic (antiferromagnetic) coupling. When the effective magnetic anisotropy constant increases, the resonance field of the acoustic and optic modes increases for both the ferromagnetic and antiferromagnetic couplings. The increasing of the effective magnetization results in decreasing of the resonance field of SWR mode at parallel geometry, whereas that of SWR mode increases at the perpendicular geometry. The results are compatible to the other theories and experimental results.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Interplay of pressure and temperature in modulating the magnetic properties of Cr 2 O 3

The spin-lattice interaction is pivotal in tailoring materials properties and is crucial for developing novel spintronic devices. Here, in the current work, we aim to explore the effects of pressure and temperature on the magnetic properties of Cr 2 O 3 to gain insights into its spin-lattice interaction. Through high-pressure neutron diffraction experiments, we observed an enhancement of the magnetic Bragg intensity with increasing pressure and it becomes more pronounced as the temperature increases. Results from first-principles calculations reveal a strengthening of the easy-axis magnetic anisotropy, doubling from 0 to 20 GPa. The exchange parameters, calculated based on this spin orientation, show an enhancement of the dominant magnetic interactions and an increase of magnetic ordering temperature when pressure increases. These findings suggest that the contributions from these two mechanisms are responsible for the observed increase in magnetic Bragg intensity.

Cr2O3↗
DOE OSTI2021

Charge doping effects on magnetic properties of single-crystal La 1-x Sr x (Cr 0.2 Mn 0.2 Fe 0.2 Co 0.2 Ni 0.2 )O 3 (0 ≤ x ≤ 0.5) high-entropy perovskite oxides

The observed influence of hole doping on magnetic properties is mapped for the compositionally complex high-entropy oxide ABO 3 perovskite La 1-x Sr x (Cr 0.2 Mn 0.2 Fe 0.2 Co 0.2 Ni 0.2 )O 3 (0 ≤ x ≤ 0.5). It is found that aliovalent A -site substitution is a viable means to manipulate the magnetically active B -site sublattice. A series of single-crystal films are synthesized and show a general trend toward stronger ferromagnetic response and a shift in magnetic anisotropy as the Sr concentration increases. Magnetometry demonstrates complex and nonuniform responses similar to rigid and uncoupled composites at intermediate dopings. This behavior points to the presence of locally inhomogeneous magnetic phase competition, where ferromagnetic and antiferromagnetic magnetic contributions create a frustrated matrix containing uncompensated spins at the boundaries between these regions. The observations are discussed in the context of known responses to hole doping in the less complex ternary LaT M O 3 (T M =Cr,Mn,Fe,Co,Ni) oxides, and they are found to be different from a simple sum of the doped parents. The results are summarized in a preliminary magnetic phase diagram.

36 MATERIALS SCIENCE↗
DOE OSTI2018

The relation of magnetic properties and anomalous Hall behaviors in Mn4N (200) epitaxial films

Highlights: • Ferrimagnetic Mn4N(200) were grown on MgO(100) by plasma assisted molecular beam epitaxy. • We elucidate the relation of nitrogen vacancies and the magnetism by adjusting the growth pressure. • We state the relation of longitudinal resistivity and temperature as ρ{sub xx}∝T{sup 1.9994} (T ≤ 86K) and ρ{sub xx}∝T{sup 0.3068} (T > 86K) by data fitting. • We introduce a method to estimate the Debye temperature of Mn{sub 4}N materials and the residual resistance of 0 K. • We verify the linear relation between anomalou Hall resistivity (ρ{sub AH}) and magnetization at low magnetic field. - Abstract: The Mn{sub 4}N(200) films were grown on MgO(100) substrates by molecular beam epitaxy. The saturated magnetizations are 0.735 μB/f.u. and 0.892 μB/f.u. under pressure of 7.5 × 10{sup −6} mbar–9.5 × 10{sup −6} mbar. Increasing of growth pressure enhances the magnetism of Mn{sub 4}N due to the reduction of nitrogen vacancies. Debye temperature (T{sub D}) of Mn{sub 4}N is estimated to be 86 K. The longitudinal resistivity is linear to T{sup 1.9994} when T D , which coincides with electron-electron scattering of ferromagnetic coupling. The longitudinal resistivity originates from electron-electron scattering below T{sub D} since electron-phonon scattering is frozen. The longitudinal resistivity at 0 K is about 10% lower than 5 K as 7.085 μΩ cm. Mn{sub 4}N films show obvious anomalous Hall Effect in perpendicular magnetic fields. The anomalous Hall resistivity (ρ{sub AH}) of Mn{sub 4}N film is obtained by subtracting the ordinary Hall resistivity from transverse resistivity. The ρ{sub AH} is verified to be linear to magnetization at low magnetic field strength region (0–9 KOe).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Structural Diversity and Magnetic Properties of Hybrid Ruthenium Halide Perovskites and Related Compounds

Abstract There has been a great deal of recent interest in extended compounds containing Ru 3+ and Ru 4+ in light of their range of unusual physical properties. Many of these properties are displayed in compounds with the perovskite and related structures. Here we report an array of structurally diverse hybrid ruthenium halide perovskites and related compounds: MA 2 Ru X 6 ( X =Cl or Br), MA 2 M RuX 6 ( M =Na, K or Ag; X =Cl or Br) and MA 3 Ru 2 X 9 ( X =Br) based upon the use of methylammonium (MA=CH 3 NH 3 + ) on the perovskite A site. The compounds MA 2 Ru X 6 with Ru 4+ crystallize in the trigonal space group and can be described as vacancy‐ordered double‐perovskites. The ordered compounds MA 2 M Ru X 6 with M + and Ru 3+ crystallize in a structure related to BaNiO 3 with alternating MX 6 and Ru X 6 face‐shared octahedra forming linear chains in the trigonal space group. The compound MA 3 Ru 2 Br 9 crystallizes in the orthorhombic Cmcm space group and displays pairs of face‐sharing octahedra forming isolated Ru 2 Br 9 moieties with very short Ru–Ru contacts of 2.789 Å. The structural details, including the role of hydrogen bonding and dimensionality, as well as the optical and magnetic properties of these compounds are described. The magnetic behavior of all three classes of compounds is influenced by spin–orbit coupling and their temperature‐dependent behavior has been compared with the predictions of the appropriate Kotani models.

Vishnoi, Pratap↗
DOE OSTI2021

First-principles characterization of the magnetic properties of Cu 2 (OH) 3 Br

Low-dimensional spin-1/2 transition metal oxides and oxyhalides continue to be at the forefront of research investigating nonclassical phases such as quantum spin liquids. In this work, we examine the magnetic properties of the oxyhalide Cu 2 (OH) 3 Br in the botallackite structure using first-principles density functional theory, linear spin-wave theory, and exact diagonalization calculations. This quasi-two-dimensional system consists of Cu 2+ S = 1/2 moments arranged on a distorted triangular lattice. Our exact diagonalization calculations, which rely on a first-principles-based magnetic model, generate spectral functions consistent with inelastic neutron scattering data. By performing computational experiments to disentangle the chemical and steric effects of the halide ions, we find that the dominant effect of the halogen ions is steric in the Cu 2 (OH) 3 X series of compounds.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Evolution of Micro-structure and Magnetic Properties in L1{sub 0} CoPt Nanoparticles by Au Addition

L1{sub 0} CoPt-Au nanoparticles with face-centered tetragonal (FCT) structure were synthesized by sol-gel technique at 700°C. The micro-structure and magnetism of L1{sub 0} CoPt-Au were measured by different measuring technologies. The influences of Au on the micro-structure and magnetism of L1{sub 0} CoPt nanoparticles were investigated. The Au addition promoted the formation of ordered L1{sub 0} phase CoPt nanoparticles and improved the grain size of L1{sub 0} CoPt nanoparticles When the Au content increased to 10 at.%, coercivity increased and saturation magnetization decreased, which may be originated from the increased order degree and ferrimagnetic nature of L1{sub 0} CoPt nanoparticles. Interestingly, when the Au addition was more than 10 at.%, the coercivity decreased due to the decrease of the order degree.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Curie Temperature Enhancement and Cation Ordering in Titanomagnetites: Evidence From Magnetic Properties, XMCD, and Mössbauer Spectroscopy

Previous work has documented time- and temperature-dependent variations in the Curie temperature (T c ) of natural titanomagnetites, independent of any changes in sample composition. To better understand the atomic-scale processes responsible for these variations, we have generated a set of synthetic titanomagnetites with a range of Ti, Mg, and Al substitution; a subset of samples was additionally oxidized at low temperature (150 °C). Samples were annealed at temperatures between 325 and 400 °C for up to 1,000 hr and characterized in terms of magnetic properties; Fe valence and site occupancy were constrained by X-ray magnetic circular dichroism (XMCD) and Mössbauer spectroscopy. Annealing results in large (up to ~100 °C) changes in T c , but Mössbauer, XMCD, and saturation magnetization data all demonstrate that intersite reordering of Fe 2+ /Fe 3+ does not play a role in the observed T c changes. Rather, the data are consistent with vacancy-enhanced nanoscale chemical clustering within the octahedral sublattice. This clustering may be a precursor to chemical unmixing at temperatures below the titanomagnetite binary solvus. Additionally, the data strongly support a model where cation vacancies are predominantly situated on octahedral sites, Mg substitution is largely accommodated on octahedral sites, and Al substitution is split between the two sites.

58 GEOSCIENCES↗
DOE OSTI2018

Structural description, luminescent and magnetic properties of novel 2-D coordination polymers containing thiazolo[5,4-d]thiazole rings and trivalent lanthanide ions

Highlights: • Reaction between thiazolo[5,4-d]thiazole-2,5-dicarboxylate and lanthanide ions yielded six novel coordination polymers. • Crystallization in gel improved yields and quality of products. • Dc magnetic susceptibilities (from 5 to 300 K) and luminescence spectra are reported. • Eu(III) luminescence indicated a single emitting center, in disagreement with the existence of the two crystallographically distinct ion sites. - Abstract: In this work, we have synthesized six coordination polymers [Ln{sub 2}(Thz){sub 3}·8H{sub 2}O)]·4H{sub 2}O (Ln = La{sup 3+}, Ce{sup 3+}, Nd{sup 3+}, Sm{sup 3+}, Eu{sup 3+}, Gd{sup 3+}; Thz = thiazolo[5,4-d]thiazole-2,5-dicarboxylate). These are the first structures combining this ligand with lanthanides. All compounds crystallize in the P-1 triclinic system, forming a 2-D coordination network. Luminescence spectra for the Nd{sup 3+}, Sm{sup 3+}, and Eu{sup 3+} structures show the typical transitions of these ions, through the antenna effect promoted by the ligand. The magnetic properties of Ce{sup 3+}, Nd{sup 3+}, Sm{sup 3+}, Eu{sup 3+}, Gd{sup 3+} compounds were analyzed in terms of the free ion approximation. The variable-temperature susceptibility fitted with a Curie-Weiss law shows the existence of weak magnetic interactions at low temperatures for the Ce{sup 3+}, Nd{sup 3+} and Sm{sup 3+} compounds, and paramagnetic behavior for the Gd{sup 3+} compound.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Structures and magnetic properties of iron silicide from adaptive genetic algorithm and first-principles calculations

We performed a systematic search for low-energy structures of binary iron silicide over a wide range of compositions using the crystal structure prediction method based on adaptive genetic algorithm. 36 structures with formation energies within 50 meV/atom (11 of them are within 20 meV) above the convex hull formed by experimentally known stable structures are predicted. Magnetic properties of these low-energy structures are investigated. Some of these structures can be promising candidates for rare-earth-free permanent magnet.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Relationship between nanostructure-magnetic property induced by temperature for iron oxide nanoparticles in vacuum, Ar and O 2 environments

It is known that superparamagnetic magnetite (Fe 3 O 4 ) nanoparticles (NPs) become ferromagnetic under Si 2+ ion irradiation due to particle size growth and microstructure evolution; it has been proposed that this feature could be used for in situ high temperature (up to 500 °C) radiation monitoring in the core of nuclear reactors. Herein, magnetite NPs synthesized by a nanocluster deposition system are heated to 800 °C in three different environments (argon, oxygen and vacuum), and nanostructure-magnetic property correlations are investigated by vibrating sample magnetometry, scanning electron microscopy, and X-ray diffraction. Magnetization of the NPs is increased due to the sintering and overall size growth by the agglomeration of the particles, while the morphology remains nearly unchanged up to 800 °C, with the one anomaly that zerovalent Fe appeared due to the reduction of the Fe 3 O 4 at 800 °C in vacuum. In argon and oxygen at high-temperature, antiferromagnetic hematite is created, which causes a reduction of the magnetization, and abrupt growth of particle size above 500 °C.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Electronic and magnetic properties of the RuX3 (X = Cl, Br, I) family: two siblings—and a cousin?

Abstract Motivated by reports of metallic behavior in the recently synthesized RuI 3 , in contrast to the Mott-insulating nature of the actively discussed α -RuCl 3 , as well as RuBr 3 , we present a detailed comparative analysis of the electronic and magnetic properties of this family of trihalides. Using a combination of first-principles calculations and effective-model considerations, we conclude that RuI 3 , similarly to the other two members, is most probably on the verge of a Mott insulator, but with much smaller magnetic moments and strong magnetic frustration. We predict the ideal pristine crystal of RuI 3 to have a nearly vanishing conventional nearest-neighbor Heisenberg interaction and to be a quantum spin liquid candidate of a possibly different kind than the Kitaev spin liquid. In order to understand the apparent contradiction to the reported resistivity ρ , we analyze the experimental evidence for all three compounds and propose a scenario for the observed metallicity in existing samples of RuI 3 . Furthermore, for the Mott insulator RuBr 3, we obtain a magnetic Hamiltonian of a similar form to that in the much-discussed α -RuCl 3 and show that this Hamiltonian is in agreement with experimental evidence in RuBr 3 .

36 MATERIALS SCIENCE↗
DOE OSTI2021

Synthesis, structural, and magnetic properties of Heusler-type Mn 2-x Fe 1+x Ge (0.0 ≤ x ≤ 1.0) alloys

Bulk Mn 2-x Fe 1+x Ge (0.0 ≤ x ≤ 1.0) alloys have been synthesized by arc-melting followed by a low temperature homogenization thermal annealing, whereas for comparison purposes the Mn 2 FeGe alloy was also produced in ribbon form by rapid solidification. Here, a study of the structural and magnetic properties is presented. Contrary to theoretical predictions, Mn 2 FeGe crystallizes in a hexagonal DO 19 crystal structure (space group P63/mmc) and orders ferromagnetically with a saturation magnetization (M S ) value of ~1.7 µB/f.u. in the ground state. With the substitution of Fe for Mn in bulk Mn 2-x Fe 1+x Ge, we observed an increase in the FM interactions with a maximum MS value of 5.1 µ B /f.u. for x = 1.0, and a significant progressive increase in the Curie temperature (T C ) in a wide range spanning ~200 K to over 400 K.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2019

Electrical and magnetic properties of thin films of the spin-filter material CrVTiAl

The spin-filter material CrVTiAl is a promising candidate for producing highly spin-polarized currents at room temperature in a nonmagnetic architecture. Thin films of compensated-ferrimagnetic CrVTiAl have been grown, and their electrical and magnetic properties have been studied. The resistivity shows two-channel semiconducting behavior with one disordered gapless channel and a gapped channel with activation energy ΔE = 0.1 – 0.2 eV. Magnetoresistance measurements to B = 35 T provide values for the mobilities of the gapless channel, leading to an order of magnitude difference in the carrier effective masses, which are in reasonable accord with our density-functional-theory-based results. The density of states and electronic band structure are computed for permutations of the four sublattices arranged differently along the (111) body diagonal, yielding metallic (Cr-V-Al-Ti), spin-gapless (Cr-V-Ti-Al), and spin-filtering (Cr-Ti-V-Al) phases. Robustness of the spin-gapless phase to substitutional disorder is also considered.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Effects on Glass Forming Ability, Microstructure, Crystallization Behaviors, and Magnetic Properties of Si Substituting for P in Fe-Rich Fe{sub 86}B{sub 13−x}Si{sub x}P{sub 1}Cu{sub 0.6}Hf{sub 0.4} Alloys

In the paper, we have studied the effects on glass forming ability (GFA), microstructure, crystallization behaviors, and saturation magnetization (M{sub s}) of Si substitution for P in Fe-rich Fe{sub 86}B{sub 12}Si{sub x}P{sub 1−x}Cu{sub 0.4}Hf{sub 0.6} alloys. The amorphous structure is identified by X-ray diffraction first, and the patterns with Si addition less than x = 0.75 only show one halo scattering peak at 2θ = 45°; further, the ribbons with entirely amorphous structure have been fabricated successfully and the alloys have a good GFA. Then, by differential scanning calorimetry testing, the curves show two separated exothermic peaks and the ribbons will go through a two-step crystallization before reaching stable state; further, the first peak is ensured by the crystallization of a-Fe phase while the second peak is ensured by the precipitation of FeB or Fe(BP) compounds. As Si was added, the apparent activation energy of the first crystallization (E{sub a1}) and the second crystallization (E{sub a2}) shows an increased tendency first and then decreases slightly. By comparison, as x = 0, x = 0.25, and x = 0.5, the ribbons easily form Hf{sub 3}P{sub 2} compounds during the first crystallization process simultaneously, where the ribbons of x = 0.75 and x = 1.0 are easier to finish the first crystallization for forming the uniform a-Fe phase entirely. By vibrating sample magnetometer testing, with the addition of Si, M{sub s} value shows an increased trend and reaches to the maximum about 177.5 emu/g (x = 1.0), and which shows an increased trend in the subsequent annealing process and reaches to the maximum 206.3 emu/g (x = 0), 212.3 emu/g (x = 0.25), 214.2 emu/g (x = 0.5), 214.9 emu/g (x = 0.75), and 208.3 emu/g (x = 1.0) as the annealing temperature higher than T{sub p1} but less than T{sub x2}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Pressure induced modification of electronic and magnetic properties of MnCrNbAl and MnCrTaAl

Spin-gapless semiconductor (SGS) is a new class of material that has been studied recently for potential applications in spintronics. This material behaves as an insulator for one spin channel, and as a gapless semiconductor for the opposite spin. In this work, we present results of a computational study of two quaternary Heusler alloys, MnCrNbAl and MnCrTaAl that have been recently reported to exhibit spin-gapless semiconducting electronic structure. In particular, using density functional calculations we analyze the effect of external pressure on electronic and magnetic properties of these compounds. It is shown that while these two alloys exhibit nearly SGS behavior at optimal lattice constants and at negative pressure (expansion), they are half-metals at equilibrium, and magnetic semiconductors at larger lattice constant. At the same time, reduction of the unit cell volume has a detrimental effect on electronic properties of these materials, by modifying the exchange splitting of their electronic structure and ultimately destroying their half-metallic/semiconducting behavior. Thus, our results indicate that both MnCrNbAl and MnCrTaAl may be attractive for practical device applications in spin-based electronics, but a potential compression of the unit cell volume (e.g. in thin-film applications) should be avoided.

Materials Science↗
DOE OSTI2024

Magnetic properties of the quasi-XY Shastry-Sutherland magnet ER 2 Be 2 SiO 7

Polycrystalline and single-crystal samples of the insulating Shastry-Sutherland compound Er 2 ⁢Be 2 ⁢SiO 7 were synthesized via a solid-state reaction and the floating zone method, respectively. The crystal structure, Er single-ion anisotropy, zero-field magnetic ground state, and magnetic phase diagrams along high-symmetry crystallographic directions were investigated with bulk measurement techniques, x-ray and neutron diffraction, and neutron spectroscopy. Here, we establish that Er 2 ⁢Be 2 ⁢SiO 7 crystallizes in a tetragonal space group with planes of orthogonal Er dimers and a strong preference for the Er moments to lie in the local plane perpendicular to each dimer bond. We also find that this system has a noncollinear ordered ground state in zero field with a transition temperature of 0.841 K consisting of antiferromagnetic dimers and in-plane moments. Finally, we mapped out the H-T phase diagrams for Er 2 ⁢Be 2 ⁢SiO 7 along the directions H ∥ [001], [100], and [110]. While an increasing in-plane field simply induces a phase transition to a field-polarized phase, we identify three metamagnetic transitions in the H ∥ [001] case. Single-crystal neutron diffraction results reveal that the H ∥ [001] phase diagram can be explained predominantly by the expected field-induced behavior of classical, anisotropic moments, although the microscopic origin of one phase requires further investigation.

36 MATERIALS SCIENCE↗