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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 19 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

X-ray magnetic diffraction under high pressure

Advances in both non-resonant and resonant X-ray magnetic diffraction since the 1980s have provided researchers with a powerful tool for exploring the spin, orbital and ion degrees of freedom in magnetic solids, as well as parsing their interplay. Here, we discuss key issues for performing X-ray magnetic diffraction on single-crystal samples under high pressure (above 40 GPa) and at cryogenic temperatures (4 K). We present case studies of both non-resonant and resonant X-ray magnetic diffraction under pressure for a spin-flip transition in an incommensurate spin-density-wave material and a continuous quantum phase transition of a commensurate all-in–all-out antiferromagnet. Both cases use diamond-anvil-cell technologies at third-generation synchrotron radiation sources. In addition to the exploration of the athermal emergence and evolution of antiferromagnetism discussed here, these techniques can be applied to the study of the pressure evolution of weak charge order such as charge-density waves, antiferro-type orbital order, the charge anisotropic tensor susceptibility and charge superlattices associated with either primary spin order or softened phonons.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Electronically- and crystal-structure-driven magnetic structures and physical properties of RScSb (R = rare earth) compounds. A neutron diffraction, magnetization and heat capacity study

The synthesis of the new equiatomic RScSb ( R = La-Nd, Sm, Gd-Tm, Lu, Y) compounds has been recently reported. These rare earth compounds crystallize in two different crystal structures, adopting the CeScSi-type ( I 4/ mmm) for the lighter R (La-Nd, Sm) and the CeFeSi-type (P4 /nmm) structure for the heavier R ( R = Gd-Tm, Lu, Y). Here we report the results of neutron diffraction, magnetization and heat capacity measurements on some of these compounds ( R = Ce, Pr, Nd, Gd and Tb). Band structure calculations have also been performed on CeScSb and GdScGe (CeScSi-type), and on GdScSb and TbScSb (CeFeSi-type) to compare and understand the exchange interactions in CeScSi and CeFeSi structure types. The neutron diffraction investigation shows that all five compounds order magnetically, with the highest transition temperature of 66 K in TbScSb and the lowest of about 9 K in CeScSb. The magnetic ground state is simple ferromagnetic (τ = [0 0 0]) in CeScSb, as well in NdScSb for 32 >T > 22 K. Below 22 K a second magnetic transition, with propagation vector τ = [¼ ¼ 0], appears in NdScSb. PrScSb has a magnetic structure within, determined by mostly ferromagnetic interactions and antiferromagnetic alignment of the Pr-sites connected through the I-centering ( τ = [1 0 0]). A cycloidal spiral structure with a temperature dependent propagation vector τ = [δ δ ½] is found in TbScSb. The results of magnetization and heat capacity lend support to the main conclusions derived from neutron diffraction. As inferred from a sharp peak in magnetization, GdScSb orders antiferromagnetically at 56 K. First principles calculations show lateral shift of spin split bands towards lower energy from the Fermi level as the CeScSi-type structure changes to the CeFeSi-type structure. This rigid shift may force the system to transform from exchange split ferromagnetic state to the antiferromagnetic state in RScSb compounds (as seen for example in GdScSb and TbScSb) and is proposed to explain the change-over from a ferromagnetic structure as found in the CeScSi-type compounds CeScSb and NdScSb to the antiferromagnetic state as found in TbScSb and GdScSb.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Nanoscale Antiferromagnetic Domain Imaging using Full-Field Resonant X-ray Magnetic Diffraction Microscopy

The physical properties of magnetic materials frequently depend not only on the microscopic spin and electronic structures, but also on the structures of mesoscopic length scales that emerge, for instance, from domain formations, or chemical and/or electronic phase separations. However, experimental access to such mesoscopic structures is currently limited, especially for antiferromagnets with net zero magnetization. Here, full-field microscopy and resonant magnetic X-ray diffraction are combined to visualize antiferromagnetic (AF) domains of the spin–orbit Mott insulator Sr 2 IrO 4 with area over ≈0.1 mm 2 and with spatial resolution as high as ≈150 nm. With the unprecedented wide field of views and high spatial resolution, an intertwining of two AF domains on a length comparable to the measured average AF domain wall width of 545 nm is revealed. This mesoscopic structure comprises a substantial portion of the sample surface, and thus can result in a macroscopic response unexpected from its microscopic magnetic structure. In particular, the symmetry analysis presented in this work shows that the inversion symmetry, which is preserved by the microscopic AF order, becomes ill-defined at the mesoscopic length scale. We report this result underscores the importance of this novel technique for a thorough understanding of the physical properties of antiferromagnets.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Ultrafast Self-Induced X-Ray Transparency and Loss of Magnetic Diffraction

Using ultrafast ≃2.5 fs and ≃25 fs self-amplified spontaneous emission pulses of increasing intensity and a novel experimental scheme, we report the concurrent increase of stimulated emission in the forward direction and loss of out-of-beam diffraction contrast for a Co/Pd multilayer sample. The experimental results are quantitatively accounted for by a statistical description of the pulses in conjunction with the optical Bloch equations. Here, the dependence of the stimulated sample response on the incident intensity, coherence time, and energy jitter of the employed pulses reveals the importance of increased control of x-ray free electron laser radiation.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2014

Development of MnBi permanent magnet: Neutron diffraction of MnBi powder

MnBi attracts great attention in recent years for its great potential as permanent magnet materials. MnBi phase is difficult to obtain because of the rather drastic peritectic reaction between Mn and Bi. In this paper, we report our effort on synthesizing high purity MnBi compound using conventional powder metallurgical approaches. Neutron diffraction was carried out to investigate the crystal and nuclear structure of the obtained powder. The result shows that the purity of the obtained powder is about 91 wt. % at 300 K, and the magnetic moment of the Mn atom in MnBi lattice is 4.424 and 4.013 μ{sub B} at 50 K and 300 K, respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Imaging antiferromagnetic antiphase domain boundaries using magnetic Bragg diffraction phase contrast

Manipulating magnetic domains is essential for many technological applications. Recent breakthroughs in Antiferromagnetic Spintronics brought up novel concepts for electronic device development. Imaging antiferromagnetic domains is of key importance to this field. Unfortunately, some of the basic domain types, such as antiphase domains, cannot be imaged by conventional techniques. Herein, we present a new domain projection imaging technique based on the localization of domain boundaries by resonant magnetic diffraction of coherent X rays. Contrast arises from reduction of the scattered intensity at the domain boundaries due to destructive interference effects. We demonstrate this approach by imaging antiphase domains in a collinear antiferromagnet Fe 2 Mo 3 O 8 , and observe evidence of domain wall interaction with a structural defect. Here, this technique does not involve any numerical algorithms. It is fast, sensitive, produces large-scale images in a single-exposure measurement, and is applicable to a variety of magnetic domain types.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

Suppression of magnetic order in CaCo 1.86 As 2 with Fe substitution: Magnetization, neutron diffraction, and x-ray diffraction studies of Ca ( Co 1 – x Fe x ) y As 2

Magnetization, neutron diffraction, and high-energy x-ray diffraction results for Sn-flux grown single-crystal samples of Ca(Co 1–x Fe x ) y As 2 , 0 ≤ x ≤ 1, 1.86 ≤ y ≤ 2, are presented and reveal that A-type antiferromagnetic order, with ordered moments lying along the c axis, persists for x ≲ 0.12(1). The antiferromagnetic order is smoothly suppressed with increasing x, with both the ordered moment and Néel temperature linearly decreasing. Stripe-type antiferromagnetic order does not occur for x ≤ 0.25, nor does ferromagnetic order for x up to at least x = 0.104, and a smooth crossover from the collapsed-tetragonal (cT) phase of CaCo 1.86 As 2 to the tetragonal (T) phase of CaFe 2 As 2 occurs. Furthermore, these results suggest that hole doping CaCo 1.86 As 2 has a less dramatic effect on the magnetism and structure than steric effects due to substituting Sr for Ca.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

A facility for X-ray diffraction in magnetic fields up to 25 T and temperatures between 15 and 295 K

A facility for X-ray diffraction has been developed at the National High Magnetic Field Laboratory. It brings diffraction capability to the 25 T Florida split coil magnet and implements temperature control in a range of 15–295 K using a cold finger helium cryostat. This instrument represents an alternative to pulsed magnetic field systems, and it exceeds the static magnetic fields currently available at synchrotron facilities. Magnetic field compatibility of an X-ray source and detectors with the sizable magnetic fringe fields emanating from the magnet constrained the design of the diffractometer.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2025

Investigating Quantum Materials with Half-Polarized Diffraction and magnetic PDF analysis at the HB-2A Neutron Powder Diffractometer

Local magnetic ordering and anisotropy is often central to the emergent behavior and subsequent functional properties in quantum materials and beyond. Neutron powder diffraction provides a straightforward yet extremely powerful technique for quantitative measurements of microscopic magnetic properties. The HB-2A powder diffractometer located at the High Flux Isotope Reactor in ORNL is traditionally utilized for long-range magnetic structure determination. Recently these capabilities have been extended to include methods aimed at accessing local magnetism: Half- polarized neutron powder diffraction (pNPD) and magnetic pair distribution function (mPDF) analysis. These two distinct techniques are possible on HB-2A due to the versatility of the instrument’s reciprocal space coverage, resolution and novel ultra-low temperature multi-sample changers that operate down to dilution refrigerator temperatures. This provides unique capabilities not found on any powder diffraction instrument and is particularly well suited to investigations of magnetic quantum materials. The development and implementation of these techniques will be discussed with a series of science case examples ranging from geometric frustrated magnets to magnetic metal-organic frameworks. Data reduction and analysis tools will be presented that enable the extraction of the local site susceptibility tensor and local spin-spin correlations in real space. Finally, potential combinations of these techniques in the form of half-polarized magnetic pair distribution function (pmPDF) analysis will be considered. Looking forward, HB-2A is undergoing a detector upgrade that will be in the user program by 2026. This will offer an order of magnitude increase in count rates to further aid the development of these often low signal measurements and provide new scientific capabilities.

Neutron Scattering↗
DOE OSTI2016

Room temperature neutron diffraction and magnetic studies of multiferroic Pb{sub 0.9}Bi{sub 0.1}Fe{sub 0.55}Nb{sub 0.45}O{sub 3} solid solution

The Pb{sub 0.9}Bi{sub 0.1}Fe{sub 0.55}Nb{sub 0.45}O{sub 3} (PBFNO) solid solution was synthesized by single step solid state reaction method and the optimized parameters are 700°C for 2hr (calcination) and 800°C for 3hr (sintering). The formation of desired material was confirmed using X-Ray Diffraction (XRD) and Neutron Diffraction (ND) studies. The structural and magnetic properties of the sintered pellets were investigated at room temperature (RT) through XRD, ND and Magnetic (M-H) studies. The structural analysis was carried out by Rietveld refinement through the Full Prof program. Rietveld refined XRD and ND patterns confirms the monoclinic structure with Cm space group and obtained cell parameters from the ND data are a = 5.651(2) Å, b = 5.658(2) Å, c = 4.005(1) Å and α = 90°, β = 89.98(1)°, γ = 90°. RT M-H curve studies have been carried out. It shows the clear opening of hysteresis (M–H) loop, is evidenced as the existence of weak ferromagnetism at RT. The M-H data shows existence weak ferromagnetism embedded in an antiferromagnetic matrix structure. The dielectric constant with frequency shows the formation of barrier layers at the grain and grain boundary interfaces gives rise to interfacial space charge polarization.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2014

Low temperature crystal structure and magnetic properties of RAl{sub 2}

Low temperature crystal structure and magnetic properties of RAl{sub 2} (R = Pr and Nd) have been studied using temperature dependent powder x-ray diffraction, magnetization, and heat capacity measurements. Unlike PrAl{sub 2}, NdAl{sub 2} retains cubic MgCu{sub 2}-type structure from room temperature down to 5 K, which is also confirmed from first principles electronic structure calculations. The magnetization measurements show both PrAl{sub 2} and NdAl{sub 2} order ferromagnetically at T{sub C} = 32 K and 77 K, respectively. However, the magnetization measurements show the former is a hard ferromagnet compared to the latter which is a soft ferromagnetic material. The magnetic entropy change obtained from heat capacity measurements at ΔH = 30 kOe for PrAl{sub 2} and NdAl{sub 2} are 3.15 J mol{sup −1} K{sup −1} and 1.18 J mol{sup −1} K{sup −1}, respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

Neutron Diffraction and Magnetic Susceptibility Studies on a High-Voltage Li 1.2 Mn 0.55 Ni 0.15 Co 0.10 O 2 Lithium Ion Battery Cathode: Insight into the Crystal Structure

Lithium- and manganese-rich oxides undergo structural transformation and/or atomic rearrangements during the delithiation/lithiation process and ultimately suffer from several issues such as first cycle irreversible capacity and voltage fade. In order to understand the mechanism of these issues, perception of a detailed crystal structure of pristine material is obviously demanding. In this study, combined powder neutron diffraction (ND) and temperature-dependent magnetic susceptibility techniques were employed to investigate the structure of a pristine lithium- and manganese-rich Li1.2Mn0.55Ni0.15Co0.10O2 cathode oxide. Rietveld refinement on the experimental ND pattern yields good fits by considering either Li2MO3 (M = Co, Mn, Ni) type monoclinic (C2/m space group) phase with 1% of Ni residing in the 4h lithium site or a composite structure consisting of 50% of Li2MnO3 type monoclinic (C2/m space group) and 50% LiMO2 (M = Co, Mn, Ni) type trigonal (R$\bar{3}$m space group) structure. In the composite structure, 3% Li/Ni site exchange in the trigonal phase is also proposed. Further, temperature-dependent dc magnetic susceptibility shows Curie–Weiss paramagnetic behavior at T ≥ 100 K, and no ordering/deviation of the field cooling (FC) curve in the temperature range 2–320 K indicates the random distribution of metal ions in the transition metal (TM) layer in the trigonal phase. Bifurcation of the zero-field cooling (ZFC) curve from the FC curve showing a magnetic ordering at TN 50 K reveals the presence of cation ordering in the TM layers arising from a distinct Li2MnO3-like phase. These results suggest that the lithium- and manganese-rich oxide with a composition Li1.2Mn0.55Ni0.15Co0.10O2 is more likely a composite of monoclinic and trigonal phases. The report also highlights the unique materials diagnostic capability of combined ND and magnetic susceptibility techniques to obtain detailed structural information of complex oxide systems.

Mohanty, Debasish↗
DOE OSTI2016

Structure and magnetic properties of new Be-substituted langasites A{sub 3}Ga{sub 3}Ge{sub 2}BeO{sub 14} (A=Pr, Nd, and Sm)

Langasites have been studied extensively in past for their functional properties and use in telecommunication. A thorough understanding of their ground state is limited by the difficulty in synthesizing new members belonging to this series due to the formation of competing phases such as the garnets. Three magnetic langasites A{sub 3}Ga{sub 3}Ge{sub 2}BeO{sub 14} (A=Pr, Nd, and Sm) and a non-magnetic lattice standard La{sub 3}Ga{sub 3}Ge{sub 2}BeO{sub 14} were synthesized using the ceramic method. These were further characterized by X-ray diffraction, magnetization, magnetic susceptibility and heat capacity measurements. All three langasites exhibit net antiferromagnetic interactions at low temperatures and no evidence of long range magnetic ordering was observed down to 0.350 K. - Graphical abstract: Kagome network formed by the magnetic ions in the new Be-langasites. The ground states of three new members were explored using different physical property measurements such as X-ray diffraction, magnetization, magnetic susceptibility and heat capacity (a–d show refinement patterns for the langasites). These can be added to the list of candidate spin liquid materials. - Highlights: • Four new langasites A{sub 3}Ga{sub 3}Ge{sub 2}BeO{sub 14} (A=La, Pr, Nd, and Sm) were synthesized. • These were characterized using physical and magnetic property measurements. • These langasites exhibit net antiferromagnetic interactions at low temperatures. • No evidence of long range magnetic ordering was observed down to 0.350 K. • Can be potential Spin liquid candidates.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Strong spin-lattice coupling in CrSiTe{sub 3}

CrSiTe{sub 3} has attracted recent interest as a candidate single-layer ferromagnetic semiconductor, but relatively little is known about the bulk properties of this material. Here, we report single-crystal X-ray diffraction, magnetic properties, thermal conductivity, vibrational, and optical spectroscopies and compare our findings with complementary electronic structure and lattice dynamics principles calculations. The high temperature paramagnetic phase is characterized by strong spin-lattice interactions that give rise to glassy behavior, negative thermal expansion, and an optical response that reveals that CrSiTe{sub 3} is an indirect gap semiconductor with indirect and direct band gaps at 0.4 and 1.2 eV, respectively. Measurements of the phonons across the 33 K ferromagnetic transition provide additional evidence for strong coupling between the magnetic and lattice degrees of freedom. The Si-Te stretching and Te displacement modes are sensitive to the magnetic ordering transition, a finding that we discuss in terms of the superexchange mechanism. Spin-lattice coupling constants are also extracted.

36 MATERIALS SCIENCE↗