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At least 1,207 records · Page 67
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Ultrawide Temperature Range Super-Invar Behavior of R 2 (Fe,Co) 17 Materials ( R = Rare Earth)

Super Invar (SIV), i.e., zero thermal expansion of metallic materials underpinned by magnetic ordering, is of great practical merit for a wide range of high precision engineering. However, the relatively narrow temperature window of SIV in most materials restricts its potential applications in many critical fields. Here, we demonstrate the controlled design of thermal expansion in a family of R 2 (Fe,Co) 17 materials (R=rare Earth). We find that adjusting the Fe-Co content tunes the thermal expansion behavior and its optimization leads to a record-wide SIV with good cyclic stability from 3–461 K, almost twice the range of currently known SIV. In situ neutron diffraction, Mössbauer spectra and first-principles calculations reveal the 3d bonding state transition of the Fe-sublattice favors extra lattice stress upon magnetic ordering. On the other hand, Co content induces a dramatic enhancement of the internal molecular field, which can be manipulated to achieve “ultrawide” SIV over broad temperature, composition and magnetic field windows. Furthermore, these findings pave the way for exploiting thermal-expansion-control engineering and related functional materials.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Crystallographic, electronic, thermal, and magnetic properties of single-crystal SrCo 2 As 2

In tetragonal SrCo 2 As 2 single crystals, inelastic neutron scattering measurements demonstrated that strong stripe-type antiferromagnetic (AFM) correlations occur at a temperature T = 5 K [W. Jayasekara et al., arXiv:1306.5174] that are the same as in the isostructural AFe 2 As 2 (A = Ca, Sr, Ba) parent compounds of high-T c superconductors. This surprising discovery suggests that SrCo 2 As 2 may also be a good parent compound for high-T c superconductivity. Here, structural and thermal expansion, electrical resistivity ρ, angle-resolved photoemission spectroscopy (ARPES), heat capacity C p , magnetic susceptibility χ, 75 As NMR and neutron diffraction measurements of SrCo 2 As 2 crystals are reported together with LDA band structure calculations that shed further light on this fascinating material. The c-axis thermal expansion coefficient α c is negative from 7 to 300 K, whereas α a is positive over this T range. The ρ(T) shows metallic character. The ARPES measurements and band theory confirm the metallic character and in addition show the presence of a flat band near the Fermi energy E F . The band calculations exhibit an extremely sharp peak in the density of states D(E F ) arising from a flat d x 2 -y 2 band. A comparison of the Sommerfeld coefficient of the electronic specific heat with χ(T → 0) suggests the presence of strong ferromagnetic itinerant spin correlations which on the basis of the Stoner criterion predicts that SrCo 2 As 2 should be an itinerant ferromagnet, in conflict with the magnetization data. The χ(T) does have a large magnitude, but also exhibits a broad maximum at 115 K suggestive of dynamic short-range AFM spin correlations, in agreement with the neutron scattering data. The measurements show no evidence for any type of phase transition between 1.3 and 300 K and we propose that metallic SrCo 2 As 2 has a gapless quantum spin-liquid ground state.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

A prototype system for dynamically polarized neutron protein crystallography

The sensitivity of Neutron Macromolecular Crystallography to the presence of hydrogen makes it a powerful tool to complement X-ray crystallographic studies using protein crystals. The power of this technique is currently limited by the relative low neutron flux provided by even the most powerful neutron sources. The strong polarization dependence of the neutron scattering cross section of hydrogen will allow us to use Dynamic Nuclear Polarization to dramatically improve the signal to noise ratio of neutron diffraction data, delivering order of magnitude gains in performance, and enabling measurements of radically smaller crystals of larger protein systems than are possible today. Here, we present a prototype frozen spin system, built at Oak Ridge National Laboratory to polarize single protein crystals on the IMAGINE beamline at the High Flux Isotope Reactor (HFIR). Details of the design and construction will be described, as will the performance of the system offline and during preliminary tests at HFIR.

47 OTHER INSTRUMENTATION↗
DOE OSTI2017

Characterization of Crystallographic Structures Using Bragg-Edge Neutron Imaging at the Spallation Neutron Source

Over the past decade, wavelength-dependent neutron radiography, also known as Bragg-edge imaging, has been employed as a non-destructive bulk characterization method due to its sensitivity to coherent elastic neutron scattering that is associated with crystalline structures. Several analysis approaches have been developed to quantitatively determine crystalline orientation, lattice strain, and phase distribution. In this study, we report a systematic investigation of the crystal structures of metallic materials (such as selected textureless powder samples and additively manufactured (AM) Inconel 718 samples), using Bragg-edge imaging at the Oak Ridge National Laboratory (ORNL) Spallation Neutron Source (SNS). Firstly, we have implemented a phenomenological Gaussian-based fitting in a Python-based computer called iBeatles. Secondly, we have developed a model-based approach to analyze Bragg-edge transmission spectra, which allows quantitative determination of the crystallographic attributes. Moreover, neutron diffraction measurements were carried out to validate the Bragg-edge analytical methods. These results demonstrate that the microstructural complexity (in this case, texture) plays a key role in determining the crystallographic parameters (lattice constant or interplanar spacing), which implies that the Bragg-edge image analysis methods must be carefully selected based on the material structures.

47 OTHER INSTRUMENTATION↗
DOE OSTI2018

Magnetic structure of a non-centrosymmetric CePtSi 3

Neutron diffraction experiments have been performed on single crystalline samples of CePtSi 3 . We found that the incommensurate magnetic propagation vector τ 1 = (±0.283, 0, 0) in the phase I (2.2 ~ 4.8 K) switches to the commensurate vectors τ 2 = (±0.25, 0, 0) and τ 3 = (±0.25, 0, ±1) in the phase III (~ 2.8 K) at zero field. Although the magnetic structure of CePtSi 3 in the phase I is a spin density wave similar to those in CeRhSi 3 , CeIrSi 3 , and CePdSi 3 , the magnetic structure in the phase III is commensurate unlike other CeTSi 3 (T = Rh, Ir, Pd) compounds.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Antiferromagnetic Spin Correlations Between Corner-Shared [FeO 5 ] 7- and [FeO 6 ] 9- Units, in the Novel Iron-Based Compound: BaYFeO 4

A novel quaternary compound in the Ba–Y–Fe-O phase diagram was synthesized by solid-state reaction and its crystal structure was characterized using powder X-ray diffraction. The crystal structure of BaYFeO 4 consists of a unique arrangement of Fe 3+ magnetic ions, which is based on alternate corner-shared units of [FeO 5 ] 7– square pyramids and [FeO 6 ] 9– octahedra. This results in the formation of stairwise channels of FeO polyhedra along the b crystallographic axis. The structure is described in an orthorhombic crystal system in the space group Pnma with lattice parameters a = 13.14455(1) Å, b = 5.694960(5) Å, and c = 10.247630(9) Å. The temperature-dependent magnetic susceptibility data reveal two antiferromagnetic (AFM) transitions at 33 and 48 K. An upturn in the magnetic susceptibility data above these transitions is observed, which does not reach its maximum even at 390 K. The field-dependent magnetization data at both 2 and 300 K show a nearly linear dependence and do not exhibit significant hysteresis. Heat capacity measurements between 2 and 200 K reveal only a broad anomaly without any indication of long-range ordering. The latter data set is not in good agreement with the magnetic susceptibility data, which makes it difficult to exactly determine the magnetic ground state of BaYFeO 4 . Accordingly, a temperature-dependent neutron diffraction study is in order, which will enable resolving this issue. The theoretical study of the relative strengths of magnetic exchange interactions along various possible pathways, using extended Hückel spin dimer analysis, shows that only interactions between square pyramidal and octahedral centers are significant, and among them, the intrachannel correlations are stronger than interchannel interactions. This is the first physical property study in such a magnetic ion substructure.

Wrobel, Friederike↗
DOE OSTI2024

Noncollinear polar magnet Fe 2 (SeO 3 ) 3 (H 2 O) 3 with inequivalent Fe 3+ sites

The emergence of novel magnetic states becomes more likely when the inversion symmetry of the crystal field, relative to the center between two spins, is broken. We propose that placing magnetic spins in inequivalent sites in a polar lattice can promote a realization of nontrivial magnetic states and associated magnetic properties. To test our hypothesis, we study Fe 2 (SeO 3 )(H 2 O) 3 as a model system that displays two distinct Fe(1) and Fe(2) magnetic sites in a polar structure (R3c space group). At low fields μ 0 H≤ 0.06 T, the material undergoes an antiferromagnetic ordering with T N1 = 77 K and a second transition at T N2 ≈ 4 K. At μ 0 H≥ 0.06 T and 74 K ≤T≤ 76 K, a positive entropy change of ∼0.12 mJ mol −1 K −1 can be associated with a metamagnetic transition to possibly nontrivial spin states. At zero field, Fe(1) is nearly fully ordered at T≈ 25 K, while Fe(2) features magnetic frustration down to T = 4 K. The magnetic ground state, a result corroborated by single-crystal neutron diffraction and 57 Fe Mössbauer spectroscopy, is a noncollinear antiparallel arrangement of ferrimagnetic Fe(1)–Fe(2) dimers along the c-axis. The results demonstrate that placing distinct magnetic sites in a polar crystal lattice can enable a new pathway to modifying spin, orbital, and lattice degrees of freedom for unconventional magnetism.

Crystal lattices↗
DOE OSTI2024

Experimental evidence for nonspherical magnetic form factor in Ru 3 +

The Mott insulator ..alpha..-RuCl3 has generated great interest in the community due to its possible field-induced Kitaev quantum spin liquid state. Despite enormous effort spent trying to obtain the form of the low-energy Hamiltonian, there is currently no agreed upon set of parameters which is able to explain all of the data. A key piece of missing information lies in the determination of the magnetic form factor of Ru3+, particularly for a true quantitative treatment of inelastic neutron scattering data. Here we present the experimentally derived magnetic form factor of Ru3+ in the low spin 4d5 state using polarized neutron diffraction within the paramagnetic regime on high-quality single crystals of ..alpha..-RuCl3. We observe strong evidence of an anisotropic form factor, expected of the spin-orbit coupled jeff=12 ground state. We model the static magnetization density in increasing complexity from simple isotropic cases, to a multipolar expansion, and, finally, ab initio calculations of the generalized jeff=12 ground state. Comparison of both single ion models and inclusion of Cl- anions support the presence of hybridization of Ru3+ with the surrounding Cl- ligands.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Antiferromagnetism in the kagome-lattice compound α-Cu 3 Mg(OH) 6 Br 2

The antiferromagnetism in α-Cu 3 Mg(OH) 6 Br 2 was studied by magnetic-susceptibility, specificheat and neutron-diffraction measurements. The crystal structure consists of Cu 2+ kagome layers with Mg 2+ ions occupying the centers of the hexagons, separated by Br 1- ions. The magnetic system orders antiferromagnetically at 5.4 K with the magnetic moments aligned ferromagnetically within the kagome planes. The ordered moment is 0.94 µ B , suggesting little quantum and geometrical fluctuations. By comparing the magnetic and specific-heat properties with those of the haydeeite, we suggest that α-Cu 3 Mg(OH) 6 Br 2 may be described by the two-dimensional spin-1/2 Heisenberg kagome model and is in the region of the ferromagnetic-order side of the phase diagram.

2-dimensional systems↗
DOE OSTI2025

Determination of Site Occupancy in the M–Pd–Zn (M = Cu, Ag, and Au) γ-Brass Phase by CALculation of PHAse Diagrams Modeling and Rietveld Refinement

The Pd–Zn γ-brass phase provides exciting opportunities for synthesizing site-isolated catalysts with precisely controlled Pd active site ensembles. Introducing a third metallic element into the γ-brass lattice further perturbs the catalytic active site ensembles. Here, in this work, we introduce coinage metallic elements M (M = Cu, Ag, and Au) into the Pd–Zn γ-brass phase and investigate the site occupation factors of each element in the γ-brass lattice. The CALculation of PHAse Diagrams (CALPHAD) modeling approach supported by energetics predicted by the density functional theory and X-ray and neutron diffraction with Rietveld refinement were used to identify the SOF on each Wyckoff site for various M amounts alloyed into the Pd–Zn γ-brass phase. The present analysis unveils the strong preference for Pd occupying the outer tetrahedral (OT) site in the γ-brass lattice, while the coinage metallic elements tend to substitute for Zn on the octahedral (OH) site. The determination of site occupancy in the bulk M–Pd–Zn γ-brass phase provides opportunities to investigate and tailor potential catalytically active site ensembles in the γ-brass phase materials.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Separation of Kondo lattice coherence from crystal electric field in CeIn 3 with Nd substitutions

The Ce m M n In 3m+2n (m=1,2;n=0,1) family has been one of the most studied families of heavy fermion compounds. This family has revealed many interesting low-temperature physics phenomena, like quantum critical points, heavy fermion superconductivity, and non-Fermi liquid behavior, when these materials are exposed to pressure, magnetic fields, and/or chemical substitution. In this work, we provide a thorough investigation of the Ce 1-x Nd x In 3 phase diagram through single crystal synthesis, x-ray diffraction, energy-dispersive spectroscopy, magnetic susceptibility, and electrical resistivity measurements. Previous electrical resistivity measurements on CeIn 3 reveal a broad maximum, T max ~50 K, which has been associated with the Kondo lattice coherence crossover and/or the crystal electric field depopulation effect as the 4f electrons condense from the high-energy quartet down to the ground state doublet. Our findings show that in the most disordered substitution region, x=0.4–0.5, these features disjoin to reveal two distinct broad humps in electrical resistivity measurements. Magnetic susceptibility and electrical resistivity data on Ce 1-x Nd x In 3 also reveal the antiferromagnetic ordering competition between CeIn 3 and NdIn 3 , where the T N of CeIn 3 is linearly suppressed to a critical concentration of x Nd ~0.6. This concentration is slightly lower than what was previously reported in nonmagnetically substituted Ce 1-x La x In 3 . Our magnetic susceptibility measurements and subsequent simulations show that in the CeIn 3 antiferromagnetic regime, x Nd ≤0.4, the Nd ions act as free paramagnets. The large magnitude of the associated paramagnetic response then masks the overlapping antiferromagnetic ordering signature of the Ce ions. Overall our study further sheds light on the underlying crystal electric field and Kondo lattice coherence interactions within the Ce m M n In 3m+2n family and could stimulate further studies of these systems via neutron diffraction or under applied pressure.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Evidence of Nematicity in K 0.8 Fe 1.7 Se 2

We proposed that the superconducting state of K 0.8 Fe 1.7 Se 2 is phase separated from a non-superconducting magnetic state. These results from a recent neutron diffraction study on a single crystal of K 0.8 Fe 1.7 Se 2 provide evidence for a continuous transition between the I 4 /m m m high temperature phase in which the Fe vacancies are randomly distributed and the I4/m vacancy ordered phase in the temperature range between T (C) and T (S). Upon cooling, the I 4 /m phase becomes more populated, increasing the √5 X√5 X 1 superlattice structure, resulting in an enhancement of the (101) superlattice peak. Moreover, the same temperature dependence is observed for the magnetic peak as well. Moreover, due to the Fe site splitting with the transition, its z-coordinate fluctuates, and so must the d xz and d y z orbitals. Finally, the orbital fluctuations couple to the magnetic ordering as seen here and may lead to a realization of nematic order in this system.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Nanometric modulations of the magnetic structure of the element Nd

The rare earth neodymium arguably exhibits the most complex magnetic ordering and series of magnetic phase transitions of the elements. Here we report the results of small-angle neutron scattering (SANS) measurements as a function of temperature and applied magnetic field to study magnetic correlations on nanometer length scales in Nd. We support these results with additional neutron diffraction, thermodynamic and synchrotron x-ray measurements. The SANS measurements reveal the presence of modulation vectors characterizing the ordered spin configuration which exhibit changes in magnitude and direction that are phase dependent. Between 5.9 and 7.6 K an additional modulation vector is observed with magnitude Q = 0.12 Å -1 . This scattering appears to originate from order of the Nd layers which contain a center of inversion. Tracking this modulation vector as a function of magnetic field indicates a phase boundary at ≈1 T. The modulation vectors observed in this study establish the presence of nanometer length scale spin textures which are likely stabilized by frustrated Ruderman–Kittel–Kasuya–Yosida (RKKY) interactions.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Dual-precipitates enhance fatigue resistance in an additively manufactured high-entropy alloy

To accomplish the intense desire of high-strength materials for enhanced energy-efficiency, recent research applies a combined strategy of additive-manufacturing and precipitation-strengthening in high entropy alloys. In a context, Al 0.2 Co 1.5 CrFeNi 1.5 Ti 0.3 nanoprecipitation-strengthened system was developed, demonstrating very convincing strength and toughness. Moreover, additive-manufacturing facilitated additional strength by well-decorated cell-boundaries with blocky L2 1 precipitates and homogeneously distributed L1 2 precipitates. However, fatigue research of this alloy remained unexplored despite being the main precursor for structural applications. In this study low-cycle fatigue behavior of this alloy in both as-built and precipitation-strengthened (aged) conditions has been explored, combined with in-situ neutron diffraction investigation. Findings revealed a substantial cyclic-stress profile and a notable fatigue-life below ±0.50% strain-amplitude, exceeding 10 5 cycles at ±0.30% strain-amplitude. These demonstrate the potential to carry higher payloads with marked engineering-reliability. Residual-stress estimation revealed strain-compatibility between the matrix and L1 2 precipitate, indicating a crack-initiation immune interface. A comparative examination of dislocation character revealed shifting towards pure edge-character in aged alloy indicates precipitates promoted planar-slip during deformation.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Persistent short-range spin fluctuation in rare-earth substituted square lattice Sr 2 ⁢Ir 0.89 ⁢Tb 0.11⁢ O 4

Sr 2 ⁢IrO 4 , a prototypical 𝐽 eff = 1/2 square lattice system, is widely studied for novel physics. While transition metal substitution effects are well explored, rare-earth doping at the Ir 4+ site is less explored. Here we present a detailed magnetization and neutron diffraction study on Sr 2 ⁢Ir 1−𝑥 ⁢Tb 𝑥 ⁢O 4 (𝑥 = 0.11). The system tends to adopt an in-plane antiferromagnetic configuration with a “++++” stacking sequence. Strong spin fluctuations persist down to the lowest measured temperature, consistent with the concave shape order parameter. A pronounced magnetic diffuse scattering rod develops along the 𝐿 direction at low temperature, indicating the formation of short-range magnetic correlations with a characteristic length of ∼ 24⁢(2) ⁢Å. In conclusion, this work provides a new pathway to exotic quantum phases in the strongly spin-orbit-coupled iridates.

Iridates↗
DOE OSTI2026

On the Ordering Mechanism of Cu + in 2D van der Waals Multiferroic CuCrP 2 S 6

CuCrP 2 S 6 is a van der Waals multiferroic where the tunable Cu + sublattice underpins its exceptional ferroelectric and electronic switching properties. Yet, the microscopic mechanism governing Cu + ordering has remained elusive. Here, we combine single-crystal X-ray and neutron diffraction with pair distribution function analysis to uncover a temperature-driven evolution of Cu + ordering, giving rise to an incommensurate quasi-antipolar phase between the paraelectric and antiferroelectric states. The modulation originates from correlated Cu + occupancy redistribution coupled to breathing distortion of surrounding S 3 triangles, establishing a symmetry-adapted lattice distortion mode. Diffuse scattering persisting over 35 K above the transition confirms that the structural instability follows an order-disorder mechanism. The spontaneous off-centering of Cu + positions CuCrP 2 S 6 as a model platform for correlated order-disorder phenomena in 2D layered ferroics, and provides design principles for next-generation memory and logic devices.

ferroelectrics↗
DOE OSTI2021

In Situ Scattering Studies of Crystallization Kinetics in a Phase-Separated Zr–Cu–Fe–Al Bulk Metallic Glass

In this work, thermal stability and the crystallization kinetics of a phase-separated Zr-Cu-Fe-Al bulk metallic glass were investigated using in situ high-energy synchrotron X-ray and neutron diffraction, as well as small-angle synchrotron X-ray scattering. It was revealed that this glass with excellent glass-forming ability possesses a two-step crystallization behavior. The crystalline products and their evolution sequence are more complicated than a homogeneous Zr-Cu-Al glass with average glass-forming ability. The experimental results indicate that a finely distributed nanometer-sized cubic Zr 2 Cu phase forms first and then transforms to a tetragonal Zr 2 Cu phase, while the matrix transforms to an orthorhombic Zr3Fe phase. The strength of the Zr-Cu-Fe-Al composite containing cubic Zr 2 Cu phase and glass matrix increases, and the plasticity also improves compared to the as-cast Zr-Cu-Fe-Al bulk metallic glass. Our results suggest that the formation of multiple and complex crystalline products would be the characteristics of the Zr-Cu-Fe-Al glass with better glass-forming ability. Our study may shed light on the synthesis of bulk-sized glass-nanocrystals composites of high strength and good plasticity.

36 MATERIALS SCIENCE↗