Search NASA⌕ Search

SEARCH · Search NASA

Results for “MAGNETIC PROPERTIES”

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 595 records · Page 33
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Role of Chiral Two-Body Currents in 6 Li Magnetic Properties in Light of a New Precision Measurement with the Relative Self-Absorption Technique

A direct measurement of the decay width of the excited $0^+_1$ state of 6 Li using the relative self-absorption technique is reported. Our value of $Γ_{γ,0^{+}_{1}} → 1^{+}_{1}$ = 8.17 (14) stat. (11) syst. eV provides sufficiently low experimental uncertainties to test modern theories of nuclear forces. The corresponding transition rate is compared to the results of ab initio calculations based on chiral effective field theory that take into account contributions to the magnetic dipole operator beyond leading order. This allows for a precision test of the impact of two-body currents that enter at next-to-leading order.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Anomalous Composition-Induced Crossover in the Magnetic Properties of the Itinerant-Electron Antiferromagnet Ca 1 - x Sr x Co 2 - y As 2

We report the inference of Ying et al. [Europhys. Lett. 104, 67005 (2013)] of a composition-induced change from c-axis ordered-moment alignment in a collinear A-type antiferromagnetic (AFM) structure at small x to ab-plane alignment in an unknown AFM structure at larger x in Ca 1-x Sr x Co 2-y As 2 with the body-centered tetragonal ThCr 2 Si 2 structure is confirmed. Our major finding is an anomalous magnetic behavior in the crossover region 0.2 ≲ x ≲ 0.3 between these two phases. Also, in this region the magnetic susceptibility vs temperature χ ab (T) measured with magnetic fields H applied in the ab plane exhibit typical AFM behaviors with cusps at the Néel temperatures of ~ 65 K, whereas χ c (T) and the low-temperature isothermal magnetization M c (H) with H aligned along the c axis exhibit extremely soft ferromagneticlike behaviors.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Syntheses, structures, and magnetic properties of cobalt(II) and nickel(II) coordination polymers based on a V-shaped ligand

Two coordination polymers [Co{sub 2}(TA)(4,4′-bipy){sub 2}(H{sub 2}O){sub 2}]·H{sub 2}O (1) and [Ni{sub 2}(TA)(4,4′-bipy){sub 2}(H{sub 2}O){sub 4}]·3H{sub 2}O (2) were prepared by hydrothermal reactions of MCl{sub 2}·6H{sub 2}O (M = Co, Ni) with a V-shaped ligand TDPA (3,3′,4,4′-thiodiphthalic anhydride) and a I-shaped N-donor co-ligand (4,4′-bipy). They were characterized by elemental analyses, thermogravinetric analyses, and magnetic behavior. As is expected, TDPA hydrolyzes into the corresponding tetra-carboxylate acid H{sub 4}TA (3,3′,4,4′-thiodiphthalic acid) during the reactions. Co{sub 2} dimer and Ni mononuclear center are connected into two-dimensional (2D) layers by H{sub 4}TA and 4,4′-bipy bridge in 1 and 2, respectively. The most amazing feature is that 1 and 2 exhibit interesting spin-canting metamagnetism and weak ferromagnetic behavior, respectively, with the critical Néel temperature of T{sub N} =4 K for 1 and T{sub N} =13 K for 2, based on variable temperature magnetic susceptibility measurements. In low mono- or dinuclear metal system, such magnetic behaviors have rare been observed. Furthermore, complex 1 will be a potential metamagnet material. - Graphical abstract: Two Co(II) and Ni(II) coordination polymers were synthesized by hydrothermal reactions from a V-shape ligand (3,3′,4,4′-thiodiphthalic anhydride) and a I-shape ligand (4,4′-bipy), which were characterized by single crystal X-ray diffraction, elemental analyses, thermogravinetric analyses, and magnetic behavior, and exhibit interesting spin-canting metamagnetism and weak ferromagnetic behavior, respectively. - Highlights: • Two Co(II) and Ni(II) coordination polymers were successfully synthesized. • Co(II) coordination polymer shows an interesting spin-canting metamagnetism. • Ni(II) coordination polymer exhibits a weak ferromagnetic behavior.

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

Effect of (1 1 1)-oriented strain on the structure and magnetic properties of La 0.7 Sr 0.3 MnO 3 thin films

Using strain, i.e. subtle changes in lattice constant in a thin film induced by the underlying substrate, opens up intriguing new ways to control material properties. We present a study of the effects of strain on structural and ferromagnetic properties of (1 1 1) pc -oriented La 0.7 Sr 0.3 MnO 3 epitaxial thin films grown on NdGaO 3 , SrTiO 3 , and DyScO 3 substrates. (The subscript pc denotes the pseudo-cubic symmetry.) The results show that La 0.7 Sr 0.3 MnO 3 assumes a monoclinic unit cell on NdGaO 3 and DyScO 3 and a rhombohedral unit cell on SrTiO 3 . For La 0.7 Sr 0.3 MnO 3 on NdGaO 3 and DyScO 3 a uniaxial magnetic anisotropy is found, while La 0.7 Sr 0.3 MnO 3 on SrTiO 3 is magnetically isotropic. The Néel model is used to explain the anisotropy of the thin films on NdGaO 3 and SrTiO 3 , however, for La 0.7 Sr 0.3 MnO 3 on DyScO 3 the effect of octahedral rotations needs to be included through the single ion model. Finally, through examination of the Curie temperature of the strained films we suggest that (1 1 1)-strain has a different effect on the Jahn-Teller splitting of e g and t 2g electron levels than what is seen in (0 0 1) pc -oriented La 0.7 Sr 0.3 MnO 3 thin films.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Characterizing physical, chemical, and magnetic properties at the nanoscale

Synchrotron light sources are extremely useful for the characterization of materials in many different research fields (including physics, chemistry, materials science, biology, medicine, geology, and cultural heritage). The evolution of technology, however, currently points toward the miniaturization of devices and molecular motors, as well as the creation (through atomic manipulation) of new materials. This brings an acute necessity for direct chemical imaging of materials, i.e., with the use of x-ray microscopy at the nanometer and atomic length scales.1, 2 Although a variety of new x-ray nanoprobes and x-ray microscopy techniques have been developed in recent years, the spatial resolution of direct chemical or magnetic contrast imaging techniques remains on the order of several nanometers. Invented in the 1980s, scanning tunneling microscopy (STM) allows a large range of materials to be viewed at the atomic level.3 STM also offers a finer degree of spatial resolution than almost any other image technique, but it is chemically ‘blind’ and thus cannot be used alone to directly identify chemical elements on a surface. For many years, researchers have attempted to solve this problem by combining STM with synchrotron x-ray excitations,4–7 and a new technique—known as synchrotron xray scanning tunneling microscopy (SX-STM)—has emerged. In this technique—which combines the chemical sensitivity of xrays with the high spatial resolution of STM—a monochromatic x-ray beam is used to illuminate a tip-sample junction, while the tip makes raster scans across the sample surface. A feedback system maintains a tip–sample separation that is typically less than 1nm. The goal is tomodulate the tunneling current through x-ray excitation and therewith obtain electronic and chemical contrast. It is difficult, however, to achieve real chemical contrast because of three serious issues. First, electrons excited by x-rays do not just tunnel into the tip, but can also be ejected from the sample and hit the sidewalls of the tip detector (which degrades the spatial resolution). Second, because photoejected electrons still provide a deceptive current signal in the far field, the STM feedback system can lift the tip out of the tunneling regime without being noticed. Last, themeasured tip current is always a convolution of the conventional tunnel current (which is related to the sample topography) and the x-ray-excited electrons (which carry the material’s chemical information).

36 MATERIALS SCIENCE↗
DOE OSTI2017

Synthesis, structure, and magnetic properties of magnesium bis-3,6-di-tert-butyl-о-benzosemiquinonate complexes with N-donor ligands

A series of six-coordinate magnesium bis-3,6-di-tert-butyl-о-benzosemiquinonate complexes with different N-donor ligands (2,2´-dipyridyl, 1,10-phenanthroline, 2,9-dimethyl-1,10-phenanthroline, pyridine, N-phenyl-1-(4-pyridinyl)methanimine) were synthesized. The molecular and crystal structures of these complexes were determined by X-ray diffraction. In the complexes with bidentate N-donor ligands, the O,O-diolate o-semiquinone ligands are cis to each other, whereas the compounds with monodentate ligands contain organic radical anions in trans positions. The specific features of magnetic exchange coupling between organic radical ligands were studied by temperature-dependent magnetic susceptibility measurements.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Structures and magnetic properties of Ni n (n = 36-40) clusters from first-principles calculations

A genetic algorithm (GA) coupled with a tight-binding (TB) interatomic potential is used to search for the low-energy structures of medium-sized Ni n (n = 36-40) clusters. Structural candidates obtained from our GA search are further optimized with first-principles calculations. The medium-sized nickel clusters ranging from 36 to 40 atoms are found to favor the double-icosahedron-based structures with a Ni7 core (a pentagonal bipyramidal structure) except Ni38 cluster. The lowest-energy structure of Ni38 can be considered to be a magic cluster, which is a typical face-centered cubic structure with large stability and magnetic moment.

Song, W.↗
DOE OSTI2016

Magnetic properties and pairing tendencies of the iron-based superconducting ladder BaFe 2 S 3 : Combined ab initio and density matrix renormalization group study

The recent discovery of superconductivity under high pressure in the two-leg ladder compound BaFe 2 S 3 [H. Takahashi et al., Nat. Mater. 14, 1008 (2015)] opens a broad avenue of research, because it represents the first report of pairing tendencies in a quasi-one-dimensional iron-based high-critical-temperature superconductor. Similarly, as in the case of the cuprates, ladders and chains can be far more accurately studied using many-body techniques and model Hamiltonians than their layered counterparts, particularly if several orbitals are active. In this publication, we derive a two-orbital Hubbard model from first principles that describes individual ladders of BaFe 2 S 3 . The model is studied with the density matrix renormalization group. These first reported results are exciting for two reasons: (i) at half-filling, ferromagnetic order emerges as the dominant magnetic pattern along the rungs of the ladder, and antiferromagnetic order along the legs, in excellent agreement with neutron experiments; and (ii) with hole doping, pairs form in the strong coupling regime, as found by studying the binding energy of two holes doped on the half-filled system. In addition, orbital selective Mott phase characteristics develop with doping, with only oneWannier orbital receiving the hole carriers while the other remains half-filled. Lastly, these results suggest that the analysis of models for iron-based two-leg ladders could clarify the origin of pairing tendencies and other exotic properties of iron-based high-critical-temperature superconductors in general.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Impact of cobalt doping on structural and magnetic properties of zinc oxide nanocomposites synthesized by mechanical ball-milling method

A series of zinc oxide (ZnO) semiconductor nanocomposite samples doped with different concentrations of cobalt (Co) were successfully synthesized via simple and highly effective mechanical ball-milling method using suitable precursors. All doped nanocomposites crystallized in hexagonal wurtzite formation of ZnO. No alteration in the wurtzite structure, with no evidence of any segregated secondary phase(s) was detected with increasing doping concentrations. This result unambiguously verified the substitution of Zn 2+ sites by Co 2+ ions in the ZnO host lattice for different doping concentrations. Moreover, room temperature ferromagnetic behavior was observed in all doped nanocomposite samples in the reported work. Present study clearly shows that mechanical ball-milling is a facile, inexpensive, eco-friendly method to synthesize crystalline and magnetic Co doped ZnO nanocomposites for next generation spin-based devices.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Structure-Related Electronic and Magnetic Properties in Ultrathin Epitaxial Ni x Fe 3–x O 4 Films on MgO(001)

Off-stoichiometric Ni x Fe 3–x O 4 ultrathin films (x < 2.1) with varying Ni content x and thickness 16 (±2) nm were grown on MgO(001) by reactive molecular beam epitaxy. Synchrotron-based high-resolution X-ray diffraction measurements reveal vertical compressive strain for all films, resulting from a lateral pseudomorphic adaption of the film to the substrate lattice without any strain relaxation. Complete crystallinity with smooth interfaces and surfaces is obtained independent of the Ni content x. For x < 1 an expected successive conversion from Fe 3 O 4 to NiFe 2 O 4 is observed, whereas local transformation into NiO structures is observed for films with Ni content x > 1. However, angle-resolved hard X-ray photoelectron spectroscopy measurements indicate homogeneous cationic distributions without strictly separated phases independent of the Ni content, while X-ray absorption spectroscopy shows that also for x > 1, not all Fe 2+ cations are substituted by Ni 2+ cations. The ferrimagnetic behavior, as observed by superconducting quantum interference device magnetometry, is characterized by decreasing saturation magnetization due to the formation of antiferromagnetic NiO parts.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Calculations of anisotropic magnetic properties using spin-orbit energy variations

We analyze several methods of obtaining the accurate relativistic total energy (TE) variations using traditional perturbation theories (PTs) and proposed coupling constant integration (CCI) methods. For this purpose, we perform benchmark calculations within the density functional theory taking the spin-orbit coupling (SOC) and its derivative as a perturbation. The TE change due to SOC addition obtained from both PTs and CCI is shown to reach the accuracy of fully self-consistent TE calculations. Similar accuracy is also obtained even for the magnetocrystalline anisotropy energy (MAE). The real advantage of the proposed methods is to use PTs and CCI methods in those electronic structure methods where accurate total energies currently cannot be obtained with required accuracy. Correspondingly, we demonstrate the applicability of suggested methods for calculations of MAE in different magnetic materials using a dynamic mean-field method. All suggested PTs and CCI methods also provide convenient site, orbital, and spin decompositions of the TE variation, creating a powerful way to analyze microscopic physics in strongly correlated materials.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Structural and magnetic properties of iodide-mediated chemically synthesized L1 2 FePt 3 nanoparticles

In this work, we study the effect of elemental iodine as a halide intermediary in the synthesis of FePt 3 nanoparticles using a co-reduction of Fe(acac) 3 and (NH 4 ) 2 PtCl 2 with 1,2-hexadecanediol. Our study shows that elemental iodine facilitates the formation of FePt 3 nanoparticles with the L1 2 structure. When iodine is not used, the as-made nanoparticles have mostly the disordered fcc FePt 3 structure. The as-made nanoparticles are ferromagnetic and have a Curie temperature close to 380 K. Annealing of the as-made nanoparticles leads to an increased particle size and a transformation to the ordered L1 2 FePt 3 phase. Nanoparticles annealed at 700°C for 30 minutes show a mixture of two magnetic phases, a ferromagnetic phase with a lower ordering temperature of ~300 K and an antiferromagnetic phase with a Néel temperature around 135 K.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of hydrogenation on the structure and magnetic properties of an iron oxide cluster

The structure and properties of the Fe8O12Hn clusters (n = 0–18) are computed using the all-electron density functional theory with the generalized gradient approximation for the exchange–correlation potential. The ground state of Fe8O12 is found to be a singlet state having a bi-capped octahedron geometry. Upon hydrogenation, the octahedral framework of Fe is retained in Fe8O12Hn up to n < 7, beyond which point the iron octahedron transforms into a cube. Hydrogen atoms are bound to oxygen atoms up to n = 12, but they bind to the faces of the Fe8 cube when n > 12. The total spin magnetic moment of a Fe8O12Hn cluster is larger than 6 μB for 1 ≤ n ≤ 18, except for n = 8 and 10, where the lowest total energy states are antiferromagnetic singlets. The reason for this deviation from the general behavior in the Fe8O12Hn series is attributed to the collective superexchange phenomenon. Surprisingly, the total spin magnetic moment of a Fe8O12Hn cluster is found to be substantially larger than the total spin magnetic moment of the bare Fe8 cluster when n = 12–18. All of the Fe8O12Hn clusters are stable with respect to an abstraction of a single hydrogen atom but are unstable toward the abstraction of an H2 dimer when n =10 and n = 14–18.

Gutsev, G. L.↗
DOE OSTI2024

Topological and magnetic properties of the interacting Bernevig-Hughes-Zhang model

We investigate the effects of electronic correlations on the Bernevig-Hughes-Zhang model using the real-space density matrix renormalization group (DMRG) algorithm. We introduce a method to probe topological phase transitions in systems with strong correlations using DMRG, substantiated by an unsupervised machine learning methodology that analyzes the orbital structure of the real-space edges. Including the full multi-orbital Hubbard interaction term, we construct a phase diagram as a function of a gap parameter (m) and the Hubbard interaction strength (U) via exact DMRG simulations on N×4 cylinders. Our analysis confirms that the topological phase persists in the presence of interactions, consistent with previous studies, but it also reveals an intriguing phase transition from a paramagnetic to a stripey antiferromagnetic topological insulator. The combination of the magnetic structure factor, strength of magnetic moments, and the orbitally resolved density, provides real-space information on both topology and magnetism in a strongly correlated system.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

N-donor co-ligands driven two new Co(II)- coordination polymers with bi- and trinuclear units: Crystal structures, and magnetic properties

Two new Co(II) coordination polymers(CPs), namely [Co{sub 2}(bpe){sub 2}(Hbppc)]{sub n} (1) and [Co{sub 3}(μ{sub 3}-OH)(bppc)(bpm)(H{sub 2}O)]·3H{sub 2}O (2) (H{sub 5}bppc=biphenyl-2,4,6,3′,5′-pentacarboxylic acid, bpe=1,2-bis(4-pyridyl)ethene, bpm=bis(4-pyridyl)amine), have been obtained and characterized by elemental analysis, single-crystal X-ray diffraction, powder X-ray diffraction (PXRD), IR spectra and thermogravimetric analysis (TGA). 1 shows a binodal (4,6)-connected fsc net with a (4{sup 4}·6{sup 10}·8)(4{sup 4}·6{sup 2}) topology, while 2 shows a binodal (5,7)-connected 3D network based on trinuclear [Co{sub 3}(μ{sub 3}-OH)]{sup 5+} units with unusual (3.4{sup 6}.5{sup 2}.6)(3{sup 2}.4{sup 6}.5{sup 7}.6{sup 5}.7) topology. Variable-temperature magnetic susceptibility measurements reveals that complex 1 shows ferromagnetic interactions between the adjacent Co(II) ions, whereas 2 is a antiferromagnetic system. - Graphical abstract: Two new Co(II) coordination polymers with bi- and trinuclear units have been obtained. 1 shows a binodal (4,6)-connected fsc net with a (4{sup 4}·6{sup 10}·8)(4{sup 4}·6{sup 2}) topology and antiferromagnetic interactions between the adjacent Co(II) ions, while 2 is a binodal (5,7)-connected 3D network with unusual (3.4{sup 6}.5{sup 2}.6)(3{sup 2}.4{sup 6}.5{sup 7}.6{sup 5}.7) topology and a ferromagnetic system. - Highlights: • Two Co(II) coordination polymers with different multimetallic clusters as building units. • A (4,6)-connected fsc net and a (5,7)-connected 3D network. • A antiferromagnetic coupling for 1 and A ferromagnetic coupling for 2.

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

Rb 2 CaCu 6 (PO 4 ) 4 O 2 , a novel oxophosphate with a shchurovskyite-type topology: synthesis, structure, magnetic properties and crystal chemistry of rubidium copper phosphates

Single crystals of Rb 2 CaCu 6 (PO 4 ) 4 O 2 were synthesized by a hydrothermal method in the multicomponent system CuCl 2 –Ca(OH) 2 –RbCl–B 2 O 3 –Rb 3 PO 4 . The synthesis was carried out in the temperature range from 690 to 700 K and at the general pressure of 480–500 atm [1 atm = 101.325 kPa] from the mixture in the molar ratio 2CuO:CaO:Rb 2 O:B 2 O 3 :P 2 O 5 . The crystals studied by single-crystal X-ray analysis were found to be monoclinic, space group C 2, a = 16.8913 (4), b = 5.6406 (1), c = 8.3591 (3) Å, β = 93.919 (3)°, V = 794.57 (4) Å 3 . The crystal structure of Rb 2 CaCu 6 (PO 4 ) 4 O 2 is similar to that of shchurovskyite and dmisokolovite and is based upon a heteropolyhedral open framework formed by polar layers of copper polyhedra linked via isolated PO 4 tetrahedra. The presence of well-isolated 2D heteropolyhedral layers in the title compound suggests low-dimensional magnetic behavior which is masked, however, by the fierce competition between multiple ferromagnetic and antiferromagnetic exchange interactions. At T C = 25 K, Rb 2 CaCu 6 (PO 4 ) 4 O 2 reaches a magnetically ordered state with large residual magnetization.

Chemistry↗
DOE OSTI2025

Crystal structure and magnetic properties of CeFe 11 M (M = Mo, W)

Tetragonal CeFe 11 Mo (struct. type ThMn 12 , a = 8.529(1) Å, c = 4.766(1) Å, V = 346.68(1) Å 3 ) and novel isostructural CeFe 11 W (a = 8.539(1) Å, c = 4.754(1) Å, V = 346.62(1) Å 3 ) are obtained in bulk, as homogenized single-phase arc-melted alloys. Here, their crystal structures are evaluated by full profile Rietveld analysis of the powder X-ray diffraction patterns which confirm that Ce occupies the 2a atomic site in both cases, whereas atomic disorder is present in the Fe-sublattice, i.e., predominantly on the dumbbell 8i site and minorly on two other sites 8j and 8f. In CeFe 11 Mo the third element, M, is mixed with Fe on the 8i dumbbell site and 8f atomic position, whereas in CeFe 11 W, M is mixed on the 8i and 8j Fe sites. In these bulk CeFe 12-x M x alloys the tetragonal structure persists at lower M content, x < 1 here, in comparison to known similar alloys, with x > 1. Because of the low M content, comparably higher values of mass magnetization and Curie temperature are achieved i.e., CeFe 11 Mo: ϭ s = 104 emu/g (14.7 µ B /f.u.), T c = 420 K and CeFe 11 W: ϭ s = 99 emu/g (16.5 µ B /f.u.), T c = 450 K. Magnetocrystalline anisotropy is uniaxial with anisotropy fields H a ∼ 14.5 and 16.5 kOe, respectively. Based on Curie temperature and magnetic anisotropy enhancements, using tungsten as the stabilizing dopant is more beneficial than molybdenum.

36 MATERIALS SCIENCE↗