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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1980

Chemical classification of iron meteorites. IX - A new group /IIF/, revision of IAB and IIICD, and data on 57 additional irons

The paper discusses the chemical classification of independent iron meteorites which include 57 meteorites based on structural observations and concentrations of Ni, Ga, Ge, and Ir. Instrumental neutron activation analysis indicates that five previously studied irons with very high Ge/Ga ratios are compositionally closely related and can be gathered together as group IIF; a previously unstudied iron, Dehesa, has the highest Ge/Ga ratios known in an iron meteorite, a ratio 18 times higher than that in CI chondrites. In terms of Ge/Ga ratios and other properties, group IIF shows genetic links to the Eagle station pallasites and CO/CV chondrites. The iron with the highest Ni concentration, Oktibbeha County, is a member of group IAB, and it extends the concentration ranges of all elements in this nonmagnetic group.

Kracher, A.↗
DOE OSTI2013

NiO/Fe(001): Magnetic anisotropy, exchange bias, and interface structure

The magnetic and structural properties of NiO/Fe epitaxial bilayers grown on MgO(001) were studied using magnetooptic Kerr effect (MOKE) and conversion electron Moessbauer spectroscopy (CEMS). The bilayers were prepared under ultra high vacuum conditions using molecular beam epitaxy with oblique deposition. Two systems were compared: one showing the exchange bias (100ML-NiO/24ML-Fe), ML stands for a monolayer, and another where the exchange bias was not observed (50ML-NiO/50ML-Fe). For both, the magnetic anisotropy was found to be complex, yet dominated by the growth-induced uniaxial anisotropy. The training effect was observed for the 100ML-NiO/24ML-Fe system and quantitatively described using the spin glass model. The composition and magnetic state of the interfacial Fe layers were studied using {sup 57}Fe-CEMS. An iron oxide phase (Fe{sup 3+}{sub 4}Fe{sup 2+}{sub 1}O{sub 7}), as thick as 31 A, was identified at the NiO/Fe interface in the as-deposited samples. The ferrimagnetic nature of the interfacial iron oxide film explains the complex magnetic anisotropy observed in the samples.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Nuclear-level densities in the {sup 49}V and {sup 57}Co nuclei on the basis of evaporated-neutron spectra in (p, n) and (d, n) reactions

The spectra of neutrons from the reactions {sup 49}Ti(p, n){sup 49}V and {sup 57}Fe (p, n){sup 57}Co were measured in the range of proton energies between 8 and 11 MeV along with their counterparts from the reactions {sup 48}Ti(d, n){sup 49}V and {sup 56}Fe (d, n){sup 57}Co at the deuteron energies of 2.7 and 3.8 MeV. These measurements were conducted with the aid of a time-of-flight fast-neutron spectrometer on the basis of the EGP-15 pulsed tandem accelerator of the Institute for Physics and Power Engineering (IPPE, Obninsk). An analysis of measured data was performed within the statistical equilibrium and preequilibrium models of nuclear reactions. The respective calculations based on the Hauser–Feshbach formalism of statistical theory were carried out with nuclear-level densities given by the generalized superfluid model of the nucleus, the backshifted Fermi-gas model, and the Gilbert–Cameron composite formula. The nuclear-level densities of {sup 49}V and {sup 57}Co and their energy dependences were determined. The results were discussed together with available experimental data and data recommended by model systematics.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2019

Synthesis, Characterization, and Magnetic Properties of A{sub 2}Co{sub 2}Fe(VO{sub 4}){sub 3} (A = Ag or Na) Alluaudite-Type Vanadates

We successfully synthesized the polycrystalline form of vanadates A{sub 2}Co{sub 2}Fe(VO{sub 4}){sub 3} (A = Ag or Na) using sol–gel method. Powder X-ray diffraction analysis allowed the identification of the alluaudite-type vanadate structure. The morphology and the elemental composition of the synthesized powders were analyzed by scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometer (EDS). The two vanadates A{sub 2}Co{sub 2}Fe(VO{sub 4}){sub 3} (A = Ag or Na) were further characterized by infrared and Raman spectroscopies to get complementary structural information. The infrared and Raman spectroscopy-observed bands were assigned to VO{sub 4}{sup 3−} vibration modes. The room temperature {sup 57}Fe Mössbauer spectroscopy confirmed the +III oxidation state of iron. Magnetic properties of these vanadates were investigated. The magnetic susceptibility data reveal that the predominant interactions in these vanadates are antiferromagnetic with a Curie−Weiss constant of θ = − 125.6 K for Na{sub 2}Co{sub 2}Fe(VO{sub 4}){sub 3} and θ = − 104.5 K for Ag{sub 2}Co{sub 2}Fe(VO{sub 4}){sub 3}. The magnetic interactions in these vanadates were discussed according to semiempirical Goodenough–Kanamori–Anderson rules (GKA).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

In-beam Mössbauer spectroscopy of {sup 57}Fe/{sup 57}Mn in MgO and NaF at Heavy-Ion Medical Accelerator in Chiba

Development of efficient ion supply of {sup 58}Fe from {sup 58}Fe(C{sub 5}H{sub 5}){sub 2}, and quick switching between therapy and material science at the Heavy-Ion Medical Accelerator in Chiba realized a new {sup 57}Mn in-beam emission Mössbauer spectroscopy measurement system. Application to simple binary chemical compounds, MgO and NaF, proved the usefulness of the system to probe chemical and physical behaviors of trace impurities in solids. Annealing of lattice defects produced by the implantation and β-decay of {sup 57}Mn and/or γ-ray emission recoil was observed by a local probe.

43 PARTICLE ACCELERATORS↗
DOE OSTI2014

Mössbauer investigations of hyperfine interactions features of {sup 57}Fe nuclei in BiFeO{sub 3} ferrite

New results of {sup 57}Fe Mössbauer studies on BiFeO{sub 3} powder sample performed at various temperatures above and below magnetic phase transitions point T{sub N} ≈ 640K are reported. We have performed self-consistent calculations of the lattice contributions to the EFG tensor, taking into account dipole moments of the O{sup 2−} and Bi{sup 3+} ions. Low-temperature {sup 57}Fe Mössbauer spectra recorded at T < T{sub N} were analyzed assuming an anharmonic cycloidal modulation of the Fe{sup 3+} magnetic moments. The cycloidal modulation of the iron spin was described with the elliptic Jacobi function sn[(±4K(m)/λ)x,m]. The good fit of the experimental spectra was obtained for the anharmonicity m = 0.44 ± 0.04 (T = 4.9K) resulting from the easy-axis magnetic anisotropy.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

57 Fe nuclear resonance vibrational spectroscopic studies of tetranuclear iron clusters bearing terminal iron( III )–oxido/hydroxido moieties

57 Fe nuclear resonance vibrational spectroscopy (NRVS) has been applied to study a series of tetranuclear iron ([Fe 4 ]) clusters based on a multidentate ligand platform (L 3− ) anchored by a 1,3,5-triarylbenzene linker and pyrazolate or (tertbutylamino)pyrazolate ligand (PzNH t Bu − ). These clusters bear a terminal Fe(III)–O/OH moiety at the apical position and three additional iron centers forming the basal positions. The three basal irons are connected with the apical iron center via a μ 4 -oxido ligand. Detailed vibrational analysis via density functional theory calculations revealed that strong NRVS spectral features below 400 cm −1 can be used as an oxidation state marker for the overall [Fe 4 ] cluster core. The terminal Fe(III)–O/OH stretching frequencies, which were observed in the range of 500–700 cm −1 , can be strongly modulated (energy shifts of 20–40 cm −1 were observed) upon redox events at the three remote basal iron centers of the [Fe 4 ] cluster without the change of the terminal Fe(III) oxidation state and its coordination environment. Therefore, the current study provides a quantitative vibrational analysis of how the remote iron centers within the same iron cluster exert exquisite control of the chemical reactivities and thermodynamic properties of the specific iron site that is responsible for small molecule activation.

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

Synthesis of α-Fe{sub 2}O{sub 3}-functionalised graphene oxide nanocomposite by a facile low temperature method and study of its magnetic and hyperfine properties

Highlights: • Synthesis of reduced graphene oxide (rGO)/α-Fe{sub 2}O{sub 3} nanocomposites (NCs) by sol–gel method. • Samples exhibited ferromagnetism originated due to surface canted spins. • rGO enhanced the value of saturation magnetization and coercivity of the bare nanoparticle. • RKKY coupling between the isolated rGO spins and the magnetic nanoparticles. - Abstract: Reduced graphene oxide/α-Fe{sub 2}O{sub 3} nanocomposites were synthesized by a simple sol–gel method. Initially, the samples were investigated by X-ray diffraction, high resolution transmission electron microscopy and Raman spectroscopy. High resolution transmission electron micrographs indicate that the magnetic nanoparticles are well dispersed in the reduced graphene oxide sheet-like structure. Fourier transform infrared spectroscopy studies corroborate the results obtained by X-ray diffraction. Temperature as well as field dependent magnetic measurements revealed ferromagnetism in the pristine α-Fe{sub 2}O{sub 3} as well as in the nanocomposite sample that is attributed to surface canted spins and defects present in the samples. The enhanced value of coercivity in case of the nanocomposite sample could be ascribed to the Ruderman–Kittel–Kasuya–Yosida type of interaction between the isolated reduced graphene oxide spin and the magnetic ions. Presence of super paramagnetic doublet as well as sextet patterns related to hematite phase is confirmed by the {sup 57}Fe-Mössbauer spectroscopy.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Interstitial Fe in MgO

Isolated {sup 57}Fe atoms were studied in MgO single-crystals by emission Mössbauer spectroscopy following implantation of {sup 57}Mn decaying to {sup 57}Fe. Four Mössbauer spectral components were found corresponding to different Fe lattice positions and/or charge states. Two components represent Fe atoms substituting Mg as Fe{sup 2+} and Fe{sup 3+}, respectively; a third component is due to Fe in a strongly implantation-induced disturbed region. The fourth component, which is the focus of this paper, can be assigned to Fe at an interstitial site. Comparison of its measured isomer shift with ab initio calculations suggests that the interstitial Fe is located on, or close to, the face of the rock-salt MgO structure. To harmonize such an assignment with the measured near-zero quadrupole interaction a local motion process (cage motion) of the Fe has to be stipulated. The relation of such a local motion as a starting point for long range diffusion is discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Probe Mössbauer Spectroscopy of BiNi{sub 0.96}{sup 57}Fe{sub 0.04}O{sub 3}

This paper presents results of a {sup 57}Fe probe Mössbauer spectroscopy study of the BiNi{sub 0.96}{sup 57}Fe{sub 0.04}O{sub 3} nickelate. The spectra measured above its TN demonstrate that Fe{sup 3+} cations heterovalently substitute for Ni{sup 2+} nickel (←Fe{sup 3+}), being stabilized on four sites of the nickel sublattice in the structure of BiNiO{sub 3}. Calculations in an ionic model with allowance for monopole and dipole contributions to the electric field gradient indicate that the parameters of electric hyperfine interactions between {sup 57}Fe probe atom nuclei reflect the specifics of the local environment of the nickel in the structure of the unsubstituted BiNiO{sub 3} nickelate. Below T{sup N}, Mössbauer spectra transform into a complex Zeeman structure, which is analyzed in terms of first-order perturbation theory with allowance for electric quadrupole interactions as a small perturbation of the Zeeman levels of the {sup 57}Fe hyperfine structure, as well as for specific features of the magnetic ordering of the Ni{sup 2+} cations in the nickelate studied.

36 MATERIALS SCIENCE↗
DOE OSTI2014

In-field {sup 57}Fe Mössbauer spectroscopy below spin-flop transition in powdered troilite (FeS) mineral

Powdered troilite (FeS), extracted from the Cape York IIIA octahedrite meteorite, was investigated employing in-field {sup 57}Fe Mössbauer spectroscopy. The study identified a typical behavior of polycrystalline antiferromagnetic material under external magnetic fields. The in-field evolution of the {sup 57}Fe Mössbauer spectra showed that the spin-flop transition in the FeS system occurs at a field higher than 5 T.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Magnetic, ferroelectric, and spin phonon coupling studies of Sr{sub 3}Co{sub 2}Fe{sub 24}O{sub 41} multiferroic Z-type hexaferrite

The magnetic, Raman, ferroelectric, and in-field {sup 57}Fe Mössbauer studies of polycrystalline multiferroic Sr{sub 3}Co{sub 2}Fe{sub 24}O{sub 41} are reported in this paper. From the magnetization studies, it is observed that the sample is soft magnetic in nature with low temperature magnetic spin transitions like longitudinal to transverse conical structure around 130 K and change in magnetic crystalline anisotropy from conical to planar structure at 250 K. Ferroelectric studies of the sample exhibit the spontaneous polarization at low temperature. Strong spin phonon and spin lattice coupling is observed through low temperature Raman spectroscopy. From the in-field {sup 57}Fe Mössbauer spectroscopy, spin up and spin down site occupations of Fe ions are calculated in the unit cell.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Enhanced magnetoelectric properties of BiFeO{sub 3} on formation of BiFeO{sub 3}/SrFe{sub 12}O{sub 19} nanocomposites

Nanocomposites (NCs) comprising (1−x) BiFeO{sub 3} (BFO) and x SrFe{sub 12}O{sub 19} (SRF) (x = 0.1, 0.2, 0.3, and 0.4) have been prepared by a sol-gel route. Presence of pure phases of both BiFeO{sub 3} (BFO) and SrFe{sub 12}O{sub 19} (SRF) in the NCs for x = 0.3 and 0.4 has been confirmed by Rietveld analysis of XRD data though a minor impurity phase is observed in the case of x = 0.1 and 0.2 NCs. Transmission electron micrographs of the NCs show that particles are mostly spherical with average size of 30 nm. M-H measurements at 300 and 10 K indicate predominantly ferrimagnetic behavior of all the NCs with an increasing trend of saturation magnetization values with increasing content of SRF. Dielectric constant (ε{sub r}) of the NCs at room temperature shows a dispersive behavior with frequency and attains a constant value at higher frequency. ε{sub r} − T measurements reveal an increasing trend of dielectric constant of the NCs with increasing temperature and show an anomaly around the antiferromagnetic transition temperature of BFO, which indicates magnetoelectric coupling in the NCs. The variation of capacitance in the presence of magnetic field confirms the enhancement of magnetoelectric effect in the NCs. {sup 57}Fe Mössbauer spectroscopy results indicate the presence of only Fe{sup 3+} ions in usual crystallographic sites of BFO and SRF.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Magnetic ordering in Ho{sub 2}Fe{sub 2}Si{sub 2}C

We have used neutron diffraction and {sup 57}Fe Mössbauer spectroscopy, complemented by magnetisation and specific heat measurements, to examine the magnetic ordering of Ho{sub 2}Fe{sub 2}Si{sub 2}C. We have established that Ho{sub 2}Fe{sub 2}Si{sub 2}C orders antiferromagnetically below T{sub N} = 16(1) K with a magnetic structure involving ordering of the Ho sublattice along the b-axis with a propagation vector k=[0 0 1/2 ]. {sup 57}Fe Mössbauer spectra collected below T{sub N} show no evidence of a magnetic splitting, demonstrating the absence of long range magnetic ordering of the Fe sublattice. A small line broadening is observed in the {sup 57}Fe spectra below T{sub N}, which is due to a transferred hyperfine field—estimated to be around 0.3 T at 10 K—from the Ho sublattice.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗