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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 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

Neutron diffraction study on magnetic structures and transitions in Sr 2 Cr 3 As 2 O 2

Sr 2 Cr 3 As 2 O 2 is composed of alternating square-lattice CrO 2 and Cr 2 As 2 stacking layers, where CrO 2 is isostructural to the CuO 2 building-block of cuprate high- T c superconductors and Cr 2 As 2 to Fe 2 As 2 of Fe-based superconductors. Current interest in this material is raised by theoretic prediction of possible superconductivity. In this neutron powder diffraction study, we discovered that magnetic moments of Cr(II) ions in the Cr 2 As 2 sublattice develop a C-type antiferromagnetic structure below 590 K, and the moments of Cr(I) in the CrO 2 sublattice form the La 2 CuO 4 -like antiferromagnetic order below 291 K. The staggered magnetic moment 2.19(4)μ B /Cr(II) in the more itinerant Cr 2 As 2 layer is smaller than 3.10(6)μ B /Cr(I) in the more localized CrO 2 layer. Furthermore, different from previous expectations, a spin-flop transition of the Cr(II) magnetic order observed at 291 K indicates a strong coupling between the CrO 2 and Cr 2 As 2 magnetic subsystems.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2026

Unveiling field-transverse spin anisotropy in the spin liquid candidate α-RuCl3 via spin Hall magnetoresistance

α-RuCl3 has emerged as a possible candidate for a quantum spin liquid (QSL) that promises exotic quasiparticles relevant for fault-tolerant quantum computation. Here, we report spin-sensitive transport measurements using a proximal spin Hall metal, platinum (Pt), to probe magnetic moments in the insulator α-RuCl3. We observe spin Hall magnetoresistance (SMR), where both the transverse and longitudinal resistivities exhibit angular oscillations between the in-plane magnetic field and the current, driven by the interplay between the spin Hall effect in Pt and local magnetic moments in α-RuCl3. These oscillations occur from 1.5 to 18 T, covering the zigzag antiferromagnetic, putative QSL, and supposedly partially field-polarized phases. The phase of the SMR oscillations suggests that the local moments, whether static or fluctuating, develop spin anisotropy with a quantization axis in-plane and largely transverse to the magnetic field across all fields from 1.5 to 18 T. Temperature dependence indicates that the spin anisotropy operates at an energy scale similar to that of the reported QSL signatures in α-RuCl3.

Idzuchi, Hiroshi [Tohoku University, Japan]↗
NASA NTRS1976

The geomagnetic dynamos of the moon and Venus - Comparisons with a recent scaling law

The evidence for the existence of an ancient lunar dynamo is reviewed along with the data on the magnetic field of Venus. These facts are then discussed in terms of Dolginov's scaling law for predicting magnetic moment of planets with a precession-driven dynamo. The precessional dynamo mechanism of Dolginov comes close to predicting the inferred magnetic moment of Venus, but this is viewed as a coincidence, for the Dolginov scaling law is based on an ad hoc force balance for which little justification is given. It assumes that the interiors of the planets have similar densities, conductivities, and precessional characteristics, whereas they clearly do not.

Russell, C. T.↗
NASA NTRS1978

The magnetic field of Mars - Mars 5 evidence re-examined

The putative magnetotail encounters of the Mars 5 spacecraft cannot be scaled to the terrestrial magnetopause. Furthermore, the magnetic field during these claimed magnetotail encounters tends to be wrapped around the planet rather than rooted in it. There is no conclusive evidence that the Mars 5 spacecraft ever entered a Martian magnetosphere. The upper limit to the Martian magnetic moment is estimated to be 2 by 10 to the 21st power gauss-cu cm, or 0.000025 times the terrestrial magnetic moment.

Russell, C. T.↗
DOE OSTI2025

Evolution of Structure and Magnetism in FeCl 2 and FeCl 3 : From Clusters to Monolayers

In this work, we address one of the most fundamental questions in cluster science─how do the structure and properties evolve from clusters to crystals? Using density functional theory (DFT), we focus our study on the evolution of structure and magnetism in iron-chloride systems, from clusters to monolayers. The choice of this system is motivated by the recent experimental confirmation of one of the author’s earlier theoretical prediction that the FeCl 2 cluster is magnetic with a spin magnetic moment of 4 μ B localized at the Fe site, while its dimer, Fe 2 Cl 4 , is antiferromagnetic. Similarly, FeCl 3 cluster is magnetic with a total spin magnetic moment of 5 μ B , with 4 μ B localized at the Fe site and 1 μ B distributed over the Cl sites. The dimer clusters Fe 2 Cl 4 and Fe 2 Cl 6 have an antiferromagnetic ground state, and upon Li-functionalization, both can be magnetically transformed from antiferromagnetic to ferromagnetic states. In contrast, FeCl 2 and FeCl 3 monolayers exhibit different magnetic ground states in their periodic forms: FeCl 2 is ferromagnetic (FM), but in FeCl 3 , the antiferromagnetic (AFM) and FM states are energetically nearly degenerate. Such a difference arises due to the different chemical coordination of the Fe atoms with the Cl atoms, caused by their different oxidation states, which is +2 in FeCl 2 and +3 in FeCl 3 , respectively. Interestingly, Li-functionalization allows both FeCl 3 and FeCl 2 monolayers to be ferromagnetic. Our study highlights that several, but not all, electronic and magnetic characteristics of isolated clusters are preserved in the extended periodic structures. This systematic investigation of iron-halide clusters is expected to inspire further experimental and theoretical exploration into the magnetism of other transition metal halides.

cluster chemistry↗
DOE OSTI2025

Scattering theory in noncanonical phase space: A Drift-Kinetic collision operator for weakly collisional plasmas

After developing a scattering theory for grazing collisions in general noncanonical phase spaces, we introduce a guiding center collision operator in five-dimensional phase space designed for plasma regimes characterized by long wavelengths (relative to the Larmor radius), low frequencies (relative to the cyclotron frequency), and weak collisionality (where repeated Coulomb collisions induce cumulatively small changes in particle magnetic moment). The collision operator is fully determined by the noncanonical Hamiltonian structure of guiding center dynamics and exhibits a metriplectic structure, ensuring the conservation of particle number, momentum, energy, and interior Casimir invariants. It also satisfies an H-theorem, allowing for deviations from an equilibrium Maxwellian distribution due to the nontrivial kernel of the noncanonical guiding center Poisson tensor, spanned by the magnetic moment. We propose that this collision operator and its underlying mathematical structure may offer valuable insight into the study of turbulence, transport, and self-organizing phenomena in both laboratory and astrophysical plasmas.

Hamiltonian mechanics↗
DOE OSTI2022

Hall Effect Study of the Metamagnetic Transition in the Sr 4 (Ru 0.99 Fe 0.01 ) 3 O 10 Nanosheet

Sr 4 (Ru 0.99 Fe 0.01 ) 3 O 10 shows a ferromagnetic (FM) transition at T C ~ 105 K with the magnetic easy axis in the ab plane, followed by a metamagnetic transition (MMT) at low temperatures when the magnetic field H is applied along the c axis, which is in sharp contrast to that of the pure Sr 4 Ru 3 O 10 , where the easy axis is along the c axis and the MMT is in the ab plane. Here, we studied the MMT in the Sr 4 (Ru 0.99 Fe 0.01 ) 3 O 10 nanosheet by the Hall effect. It was found that the ordinary Hall coefficient of Sr 4 (Ru 0.99 Fe 0.01 ) 3 O 10 is almost the same as that of the pure Sr 4 Ru 3 O 10 , while a sudden increase in the Hall resistance R xy is observed below ~50 K, above which the R xy presents the conventional anomalous Hall effect up to T C . Analysis of the results indicates that the MMT has no direct correlation to the electronic structure but closely relates to the magnetic moment locking, where the magnetic-field-induced breakdown of the locked moments is responsible for the MMT.

36 MATERIALS SCIENCE↗
DOE OSTI2018

First-Principles Study of the Structure and Magnetic Properties of Fe{sub 8}Rh{sub 8–} {sub x}Z{sub x} (Z = Mn, Pt, Co; x = 1, 2, 3) Alloys

The results of first-principles studies of the structure and magnetic properties of Fe–Rh–Z alloys conducted using the VASP package are reported. The magnetic moments and lattice parameters are determined, and the possibility of existence of stable tetragonal distortions in Fe–Rh–Z alloys with various magnetic configurations set by the level of doping with Mn, Pt, and Co is examined. It is demonstrated that the equilibrium lattice parameter and the type of magnetic ordering change with the concentration of the third element.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Prediction of novel stable Fe-V-Si ternary phase

Genetic algorithm searches based on a cluster expansion model are performed to search for stable phases of Fe-V-Si ternary. Here, we identify a new thermodynamically, dynamically and mechanically stable ternary phase of Fe 5 V 2 Si with 2 formula units in a tetragonal unit cell. The formation energy of this new ternary phase is -36.9 meV/atom below the current ternary convex hull. The magnetic moment of Fe in the new structure varies from -0.30-2.52 μ B depending strongly on the number of Fe nearest neighbors. The total magnetic moment is 10.44 μ B /unit cell for new Fe 5 V 2 Si structure and the system is ordinarily metallic.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Canted antiferromagnetic phases in the candidate layered Weyl material EuMnSb 2

EuMnSb 2 is a candidate topological material which can be tuned towards a Weyl semimetal, but there are differing reports for its antiferromagnetic (AFM) phases. The coupling of bands dominated by pure Sb layers hosting topological fermions to Mn and Eu magnetic states provides a potential path to tune the topological properties. In this study we present single-crystal neutron diffraction, magnetization, and heat-capacity data as well as polycrystalline 151 Eu Mössbauer data which show that three AFM phases exist as a function of temperature, and we present a detailed analysis of the magnetic structure in each phase. The Mn magnetic sublattice orders into a C-type AFM structure below T N Mn = 323 (1) K with the ordered Mn magnetic moment μ Mn lying perpendicular to the layers. AFM ordering of the Eu sublattice occurs below T N Eu1 = 23 (1) K with the ordered Eu magnetic moment μ Eu canted away from the layer normal and μ Mn retaining its higher temperature order. μ Eu is ferromagnetically aligned within each Eu layer but exhibits a complicated AFM layer stacking. Both of these higher-temperature phases are described by magnetic space group (MSG) $\mathcal{Pn'm'a'}$ with the chemical and magnetic unit cells having the same dimensions. Cooling below T N Eu2 =9 (1) K reveals a third AFM phase where μ Mn remains unchanged but μ Eu develops an additional substantial in-plane canting. This phase has MSG $\mathcal{P11}$ $\frac{2_1}{a′}$. We also find some evidence of short-range magnetic correlations associated with the Eu between 12 K≲ T≲ 30 K . Using the determined magnetic structures, we postulate the signs of nearest-neighbor intralayer and interlayer exchange constants and the magnetic anisotropy within a general Heisenberg model. We then discuss implications of the various AFM states in EuMnSb 2 and their potential for tuning topological properties.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Ab Initio Study of Electronic and Magnetic Properties of Germanene with Different Nonmagnetic Metal Adatoms

Electronic and magnetic properties of two-dimensional (2D) germanene (Ge) with five different adatoms have been analyzed and discussed by the DFT method. Different nonmagnetic metals adsorbed at different sites, on one hand, a magnetic moment is induced by Mg adatom in the germanene. On the other hand, the adsorptions of Al, Ga, Li, and Na show no magnetism. We further study the effect of strain on the magnetism in Mg-adsorbed germanene; we apply an isotropic tensile and compressive strain on the system. On the basis of our calculations, a tunable magnetism shows as the strain increases. The analysis of the PDOS shows that the s–p hybridization between Mg and Ge atoms results in such magnetic behavior. These magneticadsorbed germanene materials might show potential applications in the nanoscale devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Magnetic properties of Co{sub 2}{sup 2+}Co{sub 1−} {sub x}{sup 3+}Fe{sub x}{sup 3+}BO{sub 5} (x = 0.10) single crystals with a ludwigite structure

The investigation of mixed Co–Fe ludwigite single crystals shows that their magnetic properties are close to the magnetic properties of Fe{sub 3}BO{sub 5} despite the predominance of cobalt ions. The magnetic properties of Co{sub 3–} {sub x}Fe{sub x}BO{sub 5} single crystals with x = 0.10 are studied in detail. Magnetometric measurements demonstrate a strong magnetic anisotropy with easy magnetization axis b, and the orbital magnetic moment of cobalt is in a frozen state. The detected temperature dependence of the absorption of Mössbauer spectra allowed us to determine the magnetic ordering temperature, which agrees with the results of magnetization measurements (T{sub C} = 84 K).

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Complex magnetic order in nickelate slabs

Here, magnetic ordering phenomena have a profound influence on the macroscopic properties of correlated-electron materials, but their realistic prediction remains a formidable challenge. An archetypical example is the ternary nickel oxide system RNiO 3 (R = rare earth), where the period-four magnetic order with proposals of collinear and non-collinear structures and the amplitude of magnetic moments on different Ni sublattices have been subjects of debate for decades. Here we introduce an elementary model system—NdNiO 3 slabs embedded in a non-magnetic NdGaO 3 matrix—and use polarized resonant X-ray scattering (RXS) to show that both collinear and non-collinear magnetic structures can be realized, depending on the slab thickness. The crossover between both spin structures is correctly predicted by density functional theory and can be qualitatively understood in a low-energy spin model. We further demonstrate that the amplitude ratio of magnetic moments in neighbouring NiO 6 octahedra can be accurately determined by RXS in combination with a correlated double cluster model. Targeted synthesis of model systems with controlled thickness and synergistic application of polarized RXS and ab initio theory thus provide new perspectives for research on complex magnetism, in analogy to two-dimensional materials created by exfoliation.

25 ENERGY STORAGE↗
DOE OSTI2024

Site Occupancy Preference and Magnetic Properties in Nd 2 (Fe,Co) 14 B

Partial replacement of Fe by Co is an effective method to increase Curie temperature (T C ) , which improves the thermal stability of magnetic properties in Nd 2 Fe 14 B-based permanent magnets. The correlation between Fe substitution and magnetic properties has been studied in Nd 2 (Fe,Co) 14 B via a first-principles calculation. The calculated Fe substitution energies indicate that the Co atoms avoid the 8 j 2 site, which agrees with the experiments. The Co atoms are ferromagnetically coupled with Fe sublattice and show magnetic moments of about 1.2 to 1.7 μ B at different crystallographic sites, less than that of Fe (2.1–2.7 μ B ), resulting in the decrease in total magnetization at ground state (0 K) with increasing Co content. The effective exchange interaction parameter, derived from the energy difference between varied magnetic structures, increases from 7.8 meV to 17.0 meV with increasing Co content from x = 0 to x = 14 in Nd 2 Fe 14–x Co x B. This change in the effective exchange interaction parameter is responsible for the enhancement of T C in Nd 2 (Fe,Co) 14 B. The total magnetization at 300 K, derived from mean-field theory, shows a peak maximum value at x = 1 in Nd 2 Fe 14–x Co x B. The phenomenon results from the interplay between the reduction of the magnetic moment in the Fe(Co) sublattice and the enhancement of T C with increasing Co content.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Spin transition characteristics of molecular solvates of Cu{sup II} complexes with nitroxides: sensitivity to the packing type

A method for the synthesis of solvates of dinuclear heterospin complexes of bis(hexafluoroacetylacetonato)copper(II) with 2-(4-methylpyridin-3-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (L{sup Me}) and 2-(4-ethylpyridin-3-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-3-oxide-1-oxyl (L{sup Et}) of the composition [Cu(hfac){sub 2}L{sup R}]{sub 2} · Solv (Solv = benzene, bromobenzene, toluene, o-xylene, p-xylene) was developed. It was found that a decrease in temperature induces structural transformations of the solid phases of the complexes followed by significant changes in the distances between the paramagnetic centers in the intramolecular exchange clusters {Cu"2"+-O"·-} from 2.321 to 1.974 Å. As a result, the temperature dependences of the effective magnetic moment μ{sub eff}(T) exhibit magnetic features similar to spin transitions. An analysis of the shape of the μ{sub eff}(T) curves suggested that the magnetic properties of the compounds under study depend primarily on the molecular packing. A comparison of the magneto-structural correlations typical of the [Cu(hfac){sub 2}L{sup R}]{sub 2} · Solv complexes studied in this work with the data obtained earlier for analogous solvates of heterospin polymer chain complexes showed that the spin transition characteristics of the [Cu(hfac){sub 2}L{sup R}]{sub 2} · Solv systems are much less sensitive to the change of the solvent than the corresponding characteristics of the heterospin polymers containing solvate molecules in the interchain space. The magnetic characteristics of the heterospin dimer molecules depend primarily on which cavity between the dimers is filled with solvate molecules. For solvates with monoclinic symmetry, changes in the solvent molecules occupying same-type cavities have almost no effect on the spin transition characteristics in the heterospin exchange cluster.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2026

Canted antiferromagnetism and spin reorientation in corner-shared single chain quasi-one-dimensional Ba 2 ⁢FeSe 3

Here, we report the canted antiferromagnetic (AFM) structure together with a spin reorientation in a single chain quasi-one-dimensional (Q-1D) iron chalcogenide Ba 2⁢ FeSe 3 . Ba 2 ⁢FeSe 3 crystallizes in Pnma (No. 62) orthorhombic structure with linear single iron chains consisting of corner-shared distorted FeSe 4 tetrahedra along the 𝑏 axis. Ba 2 ⁢FeSe 3 is a narrow-gap semiconductor and orders AFM below 60 K. Modeling of neutron powder diffraction data reveals a canted AFM ground state of magnetic space group 𝑃⁢𝑎⁢21/𝑐 (BNS No. 14.80) with commensurate propagation vector 𝐤 =(0, $\frac{1}{2}$, 0), where the Fe ion spins are AFM aligned with up-down-up-down (↑−↓−↑−↓) sequence along the Q-1D chain direction of the 𝑏 axis. In the magnetically ordered state, the canting of magnetic moments reorients from the 𝑎⁢𝑐 plane to the 𝑎⁢𝑏 plane below 30 K, with a 10° tilting angle toward the 𝑎 axis, and the magnetic moment does not induce a net moment in either orientation. The density functional theory results indicate that an ↑−↓−↑−↓ AFM state is stabilized along the chain direction. In this work, we elucidate the unique canted AFM of the iron chalcogenide and pave the way for searching exotic physics in Q-1D Ba 2⁢ FeSe 3 .

Gao, Fei [Univ. of Texas at Dallas, Richardson, TX↗
DOE OSTI2024

Long-range three-dimensional magnetic structures of the spin S =1 hexamer cluster fedotovite-like A 2 Cu 3 O ( SO 4 ) 3 ( A 2 = K 2 , NaK, Na 2 ): A neutron diffraction study

The crystal and magnetic structures of the spin S = 1 hexamer cluster fedotovite-like A 2 Cu 3 O(SO 4 ) 3 (A 2 = K 2 , NaK, Na 2 ) were studied by neutron powder diffraction at temperatures 1.6–290 K. The crystal structures in all compounds are well refined in the monoclinic space group C2/c. The basic magnetic units of the compounds are copper hexamers, which are coupled by weak superexchange interactions giving rise to three-dimensional long-range magnetic order below 3.0 < T N < 4.7 K. We have found that for A 2 = K 2 and NaK the propagation vector of the magnetic structure is k = [0,0,0], and the coupling of the Cu hexamers is ferromagnetic (FM) along the ab diagonal and antiferromagnetic along the bc diagonal. In contrast, for A = Na the propagation vector is k = [0,1,0], and the Cu hexamers are coupled antiferromagnetically (AFM) along the ab diagonal. Further, the hexamers are formed by three Cu pairs arranged along the b axis. The calculated spin expectation values $\langle s \rangle$ for the simplest symmetric spin Hamiltonian (obtained from inelastic neutron spectroscopy) of the isolated hexamers in the mean field amounted to $\langle s \rangle$ = 3/8 for the side spins Cu1 and Cu2 and $\langle s \rangle$ = 1/4 for Cu3 in the middle. The Cu spins are FM coupled in pairs and AFM between neighboring pairs. The experimental magnetic moments of the Cu 2+ ions turn out to be not completely collinear due to spin frustrations within the weak interhexamer interactions. The sizes of magnetic moments of Cu in the hexamers determined from the diffraction data are in fair agreement with the calculated values.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Itinerant G-type antiferromagnetic order in SrCr 2 As 2

Here, neutron-diffraction and magnetic susceptibility studies of polycrystalline SrCr 2 As 2 reveal that this compound is an itinerant G-type antiferromagnet below the Néel temperature T N = 590(5) K with the Cr magnetic moments aligned along the tetragonal c axis. The system remains tetragonal to the lowest measured temperature (~12 K). The lattice parameter ratio c/a and the magnetic moment saturate at about the same temperature below ~200 K, indicating a possible magnetoelastic coupling. The ordered moment μ = 1.9(1)μ B/Cr , measured at T = 12 K, is significantly reduced compared to its localized value (4μ B/Cr ) due to the itinerant character brought about by hybridization between the Cr 3d and As 4p orbitals.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗