Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “FERROMAGNETIC MATERIALS”

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 1,801 records · Page 100
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

4 d element induced improvement of structural disorder and development of weakly reentrant spin-glass behavior in NiRuMnSn

The pursuit of efficient spin polarization in quaternary Heusler alloys with the general formula XX'YZ (where X, X', and Y are transition metals and Z is a p-block element) has been a subject of significant scientific interest. While previous studies showed that isoelectronic substitution of a 4d element in place of a 3d element in quaternary Heusler alloys improves the half-metallic ferromagnetic characteristics, our research here, on the quaternary Heusler alloy NiRuMnSn, reveals a strikingly different scenario. In this study, we present a detailed structural analysis of the material using x-ray absorption fine structure and neutron diffraction techniques which confirms the formation of a single-phase compound with 50:50 site disorder between Ni and Ru atoms at 4c and 4d sites. Contrary to expectations, our density functional theory calculations suggest a considerable decrease in spin polarization even in the ordered structure. Additionally, we report on the compound's exceptional behavior, displaying a rare reentrant spin-glass property below ~ 60 K, a unique and intriguing feature for quaternary Heusler-type compounds.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Large anomalous Nernst effect and topological Nernst effect in the noncollinear antiferromagnet NdMn 2⁢ Ge 2

ThCr 2 Si 2 -type NdMn 2 Ge 2 was recently proposed to be a magnetic skyrmion candidate exhibiting the topological Hall effect. In this work, we report magnetic, electronic, and thermoelectric measurements for NdMn 2 Ge 2 single crystals. We show that, in the canted antiferromagnetic phase and the conical magnetic phase with a large out-of-plane ferromagnetic component, this system exhibits both an anomalous Nernst effect and a topological Nernst effect. Here we argue that NdMn 2 Ge 2 is a unique magnetic material, with its topological characteristics associated with the Berry phases in both real space and momentum space.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Revealing the Nature of Antiferroquadrupolar Ordering in Cerium Hexaboride: CeB 6

The cerium hexaboride (CeB 6 ) f -electron compound displays a rich array of low-temperature magnetic phenomena, including a “magnetically hidden” order, identified as multipolar in origin via advanced x-ray scattering. From first-principles electronic-structure results, we find that the antiferroquadrupolar (AFQ) ordering in CeB 6 arises from crystal-field splitting and yields a band structure in agreement with experiments. With interactions of p electrons between Ce and B 6 being small, the electronic state of CeB 6 is suitably described as Ce(4 f 1 ) 3+ (e – )(B 6 ) 2– . The AFQ state of orbital spins is caused by an exchange interaction induced through spin-orbit interaction, which also splits the J = 5/2 state into a Γ 8 ground state and a Γ 7 excited state. Within the smallest antiferromagnetic (AFM) (111) configuration, an orbital-ordered AFQ state appears during charge self-consistency, and it supports the appearance of a “hidden” order. Furthermore hydrostatic pressure (either applied or chemically induced) stabilizes the AFM (AFQ) states over a ferromagnetic one, as observed at low temperatures.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Thickness dependent itinerant ferromagnetism in ultrathin Ba-doped SrRu O 3 films

The electronic and magnetic properties in AB⁢O 3 perovskite oxides are extremely sensitive to lattice structure, but also to dimensionality, such as the thickness in thin film-form. Here, we report the thickness-dependent electromagnetic properties of ultrathin epitaxially stabilized Sr 1-x ⁢Ba x ⁢Ru⁢O 3 (x = 0.08, 0.2) thin films on a SrTi⁢O 3 (001) substrate. The results reveal that the barium doping (0.08 ≤ x ≤ 0.20) reduces Ru⁢O 6 orthorhombic distortions existing in SrRu⁢O 3 and induces a tetragonal distortion, as evidenced by out-of-plane lattice expansion. A metal-to-insulator transition, accompanied by a ferromagnetic to nonmagnetic transition occurs with reducing film thickness from 10 to 3 unit cells for both x = 0.08 and 0.2, regardless of the doping level. The results suggest that the effects of compositional vacancies and surface/interface contributions introduced via dimensional confinement are more dominant than A-site chemical disorder or structural distortion for the loss of metallicity and ferromagnetism in ultra-thin epitaxial films.

36 MATERIALS SCIENCE↗
DOE OSTI2025

Spin-dependent dark matter scattering in quasi-two-dimensional magnets

We study the prospects of detecting dark matter coupled to the spin of the electron, such that it may scatter and excite magnons—collective excitations of electronic spins. We show that materials exhibiting long-range magnetic order where the spins are coupled only along a plane may act as directional dark matter detectors. These quasi-two-dimensional materials possess anisotropic dispersion relations and structure functions which induce a sidereal modulation in the excitation rate. We calculate the expected signal rate for some candidate (anti)ferromagnets, demonstrating a possible route to the direct detection of spin-dependent dark matter in the keV to MeV mass range.

Dark matter direct detection↗
DOE OSTI2024

Formation kinetics and thermodynamic stability of the Aurivillius compounds in Bi 4 Ti 3 O 12 –BiFeO 3 system

Abstract The Aurivillius compounds in the Bi 2 O 3 –Fe 2 O 3 –TiO 2 system, combining ferroelectric, semiconducting, and ferromagnetic properties, have attracted particular interest. Formation kinetics and thermodynamic stability are the fundamental knowledge needed for modeling and predicting the temporal microstructure and property evolution during materials processing but have not yet been addressed by quantitative experimental measurement. This article focuses on the Bi n +1 Fe n –3 Ti 3 O 3 n +3 Aurivillius compounds on the Bi 4 Ti 3 O 12 –BiFeO 3 tie‐line to elucidate the mechanisms and thermodynamic controls responsible for phase formation of compounds with various perovskite‐like layers. Five high‐purity Aurivillius compounds Bi 4 Ti 3 O 12 , Bi 5 FeTi 3 O 15 , Bi 6 Fe 2 Ti 3 O 18 , Bi 7 Fe 3 Ti 3 O 21 , and Bi 8 Fe 4 Ti 3 O 24 with integer n = 3–7 values were synthesized and their phase transformation properties and enthalpies of formation were studied by X‐ray diffraction in situ, high temperature differential scanning calorimetry, and high temperature oxide melt solution calorimetry. Thermodynamic stability of the compounds decreases with increasing n , and formation kinetics gradually slow down, demonstrating the inherent difficulty to synthesize pure Aurivillius compounds with n larger than 8. This difficulty was confirmed by an impurity phase coexisting with Bi 9 Fe 5 Ti 3 O 27 .

Gong, Weiping↗
NASA NTRS1994

Integrated, nonvolatile, high-speed analog random access memory

This invention provides an integrated, non-volatile, high-speed random access memory. A magnetically switchable ferromagnetic or ferrimagnetic layer is sandwiched between an electrical conductor which provides the ability to magnetize the magnetically switchable layer and a magneto resistive or Hall effect material which allows sensing the magnetic field which emanates from the magnetization of the magnetically switchable layer. By using this integrated three-layer form, the writing process, which is controlled by the conductor, is separated from the storage medium in the magnetic layer and from the readback process which is controlled by the magnetoresistive layer. A circuit for implementing the memory in CMOS or the like is disclosed.

Katti, Romney R.↗
DOE OSTI2024

Excitons in 2D Magnets

Theoretical abilities that we built: In our QSGW formalism, the electronic eigenfunctions are calculated self-consistently in presence of the ladder e-h vertex corrections to the screened Coulomb exchange. Charge and self-energies are recalculated iterated until the desired tolerance is achieved in the one-particle Green's function. Further, to include the multi-determinantal (spin-flip structure of multiplets) nature of many body correlations we combine QSGW with DMFT. Below we explore various classes of strongly correlated magnetic systems where excitons are sufficiently described within either the QSGW or the QSGW +DMFT approach. In the process, we establish the digrammatic requirements for a minimum-sufficient theory for describing excitons in large classes of materials.

2D magnets↗
DOE OSTI2019

Structural and magnetic properties of the CeCo 5 –CeZn 5 solid solution and potential improvements upon iron substitution

In an effort to create high-performance permanent magnets with reduced critical rare earth content, we explored the CeCo 5-x T x (T = transition metal or metalloid) family of compounds to investigate the effect of substitution on the material’s magnetic properties. In our exploration of the CeCo 5-x Zn x system, we discovered a continuous solid solution at 900 °C between the CeCo 5 and CeZn 5 binary phases with ferromagnetism existing from the CeCo 5 compound to the intermediate CeCo 2.75 Zn 2.25 compound. Single crystal studies were also conducted revealing a relatively large anisotropy field of 11.5 T at 300 K for Ce 0.96 Ta 0.04 Co 4.35 Zn 0.65 . Here, the addition of iron Ce 0.79 Ta 0.07 Co 3.77 Fe 0.89 Zn 0.47 yielded further increases in Curie temperature and saturation magnetization to 800 K and 85.5 emu/g, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Visualization and manipulation of magnetic domains in the quasi-two-dimensional material F e 3 GeT e 2

The magnetic domains in two-dimensional layered material Fe 3 GeTe 2 are studied by using a variable-temperature scanning tunneling microscope with a magnetic tip after in situ cleaving of single crystals. A stripy domain structure is revealed in a zero-field-cooled sample below the ferromagnetic transition temperature of 205 K, which is replaced by separate double-walled domains and bubble domains when cooling the sample under a magnetic field of a ferromagnetic Ni tip. The Ni tip can further convert the double-walled domain to a bubble domain pattern as well as move the Neel-type chiral bubble in submicrometer distance. The temperature-dependent evolutions of both zero-field-cooled and field-cooled domain structures correlate well with the bulk magnetization from magnetometry measurements. Furthermore, atomic resolution scanning tunneling images and spectroscopy are acquired to understand the atomic and electronic structures of the material, which are further corroborated by first-principles calculations.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Synthesis, structure and properties of the oxychalcogenide series A{sub 4}O{sub 4}TiSe{sub 4} (A=Sm, Gd, Tb, Dy, Ho, Er and Y)

Seven oxyselenide materials have been synthesised with composition A{sub 4}O{sub 4}TiSe{sub 4} (A=Sm, Gd–Er, Y) via solid state reactions of A{sub 2}O{sub 3}, TiSe{sub 2} and Se at 900 °C. They are all isostructural with Gd{sub 4}O{sub 4}TiSe{sub 4}. Structures have been refined from powder X-ray diffraction data and have monoclinic C2/m symmetry with unit cell parameters of a≈15.7 Å, b≈3.75 Å, c≈9.65 Å and β≈117.5°. They contain infinite ribbons of edge-sharing A{sub 4}O and A{sub 3}TiO tetrahedra 4 units wide, which are linked by chains of TiSe{sub 4}O{sub 2} edge-sharing octahedra. Compositions A=Gd–Ho, Y are semiconductors with conductivities 1–3 Sm{sup −1} at 300 K, with electronic band gaps of between 0.25 and 0.37 eV. Magnetic susceptibility is reported from 1.8 K to 300 K for compositions A=Gd–Ho. Rare earth moments appear to order antiferromagnetically at low temperatures with Gd and Tb showing evidence of ferromagnetism due to spin canting over a narrow temperature range close to T{sub N}. - Graphical abstract: Illustration of the A{sub 4}O{sub 4}TiSe{sub 4} crystal structure (C2/m symmetry), A{sub 4}O and A{sub 3}TiO edge sharing tetrahedral ribbons in red, chains of edge-sharing TiSe{sub 4}O{sub 2} in blue. Rare earth=green, titanium=blue, selenium=yellow, and oxygen=red. Display Omitted - Highlights: • Seven materials with A{sub 4}O{sub 4}TiSe{sub 4} (A=Sm, Gd–Er, Y) have been synthesised as bulk phases for the first time. • Materials are semiconductors and order antiferromagnetically at ∼4 K. • Structure contains M{sub 4}O tetrahedral ribbons and TiSe{sub 4}O{sub 2} 1D octahedral chains.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

New characterisation method of electrical and electronic equipment wastes (WEEE)

Highlights: ► A novel method of characterisation of components contained in WEEE has been developed. ► This technique was applied on several samples generated from different recycling plants. ► Handheld NIR and XRF were used to determine types of plastics and flame retardants. ► WEEE processing flow-sheet was suggested. - Abstract: Innovative separation and beneficiation techniques of various materials encountered in electrical and electronic equipment wastes (WEEE) is a major improvement for its recycling. Mechanical separation-oriented characterisation of WEEE was conducted in an attempt to evaluate the amenability of mechanical separation processes. Properties such as liberation degree of fractions (plastics, metals ferrous and non-ferrous), which are essential for mechanical separation, are analysed by means of a grain counting approach. Two different samples from different recycling industries were characterised in this work. The first sample is a heterogeneous material containing different types of plastics, metals (ferrous and non-ferrous), printed circuit board (PCB), rubber and wood. The second sample contains a mixture of mainly plastics. It is found for the first sample that all aluminium particles are free (100%) in all investigated size fractions. Between 92% and 95% of plastics are present as free particles; however, 67% in average of ferromagnetic particles are liberated. It can be observed that only 42% of ferromagnetic particles are free in the size fraction larger than 20 mm. Particle shapes were also quantified manually particle by particle. The results show that the particle shapes as a result of shredding, turn out to be heterogeneous, thereby complicating mechanical separation processes. In addition, the separability of various materials was ascertained by a sink–float analysis and eddy current separation. The second sample was separated by automatic sensor sorting in four different products: ABS, PC–ABS, PS and rest product. The fractions were characterised by using the methodology described in this paper. The results show that the grade and liberation degree of the plastic products ABS, PC–ABS and PS are close to 100%. Sink–float separation and infrared plastic identification equipment confirms the high plastic quality. On the basis of these findings, a global separation flow sheet is proposed to improve the plastic separation of WEEE.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗
DOE OSTI2024

Material Characterization Study of Magnetite Nanocrystals for RF Sensing

Magnetite nanocrystals show promise for electrically small gigahertz frequency applications, which could lead to miniaturizing transformer cores and new sensing technologies. This work presents a rigorous radiofrequency characterization of these nanocrystals using vector network analyzer (VNA) ferromagnetic resonance (FMR) measurements. For the first time, two different average diameters of Fe 3 O 4 nanocrystals are investigated (7.3 and 20.2 nm). When the VNA–FMR results were compared to micromagnetic simulations, the magnetic anisotropy (K 1 ) deviated from the ideal mean orientation value of K 1 /2 to K 1 /80 for the 7.3 nm nanocrystal. In contrast, the obtained magnetic anisotropy in 20.2 nm nanocrystals slightly deviated to K 1 /11 due to less structural deformations. These findings resulted in a newly proposed methodology for an approximate simulation based on VNA–FMR measurements. In addition, this work estimates the approximate amount of nanocrystals needed to measure a useful VNA–FMR spectrum.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

Refine your search to explore more results.