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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 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
DOE OSTI2018

161 Dy Time-Domain Synchrotron Mössbauer Spectroscopy for Investigating Single-Molecule Magnets Incorporating Dy Ions [ 161 Dy time-domain synchrotron Mössbauer spectroscopy as a new way forward for investigating single molecule magnets incorporating Dy ions]

Time–domain synchrotron Mössbauer spectroscopy (SMS) based on the Mössbauer effect of 161 Dy has been used to investigate the magnetic properties of a Dy III –based single–molecule magnet (SMM). The magnetic hyperfine field of [Dy(Cy 3 PO) 2 (H 2 O) 5 ]Br 3 •2 (Cy 3 PO)•2 H 2 O•2 EtOH is with B 0 =582.3(5) T significantly larger than that of the free–ion Dy III with a 6 H 15/2 ground state. This difference is attributed to the influence of the coordinating ligands on the Fermi contact interaction between the s and 4f electrons of the Dy III ion. Furthermore this study demonstrates that 161 Dy SMS is an effective local probe of the influence of the coordinating ligands on the magnetic structure of Dy–containing compounds.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2021

Magnetism and topological Hall effect in antiferromagnetic Ru 2 MnSn-based Heusler compounds

Heusler compounds and alloys based on them are of great recent interest because they exhibit a wide variety of spin structures, magnetic properties, and electron-transport phenomena. Their properties are tunable by alloying and we have investigated L2 1 -orderd compound Ru 2 MnSn and its alloys by varying the atomic Mn:Sn composition. While antiferromagnetic ordering with a Néel temperature of 361 K was observed in Ru 2 MnSn, the Mn-poor Ru 2 Mn 0.8 Sn 1.2 alloy exhibits properties of a diluted antiferromagnet in which there are localized regions of uncompensated Mn spins. Furthermore, a noncoplanar spin structure, evident from a topological Hall-effect contribution to the room-temperature Hall resistivity, is realized in Ru 2 Mn 0.8 Sn 1.2 . Finally, our combined experimental and theoretical analysis shows that in the Ru 2 Mn 0.8 Sn 1.2 alloy, the magnetic properties can be explained in terms of a noncoplanar antiferromagnetic scissor mode, which creates a small net magnetization in a magnetic field and subsequently yields a Berry curvature with a strong topological Hall effect.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Synthesis and Characterisation of Superparamagnetic MgFe{sub 2}O{sub 4} Nanoferrite

Nanocrystalline MgFe{sub 2}O{sub 4} with crystallite size of 10.4 nm was synthesised using combustion method and characterised for structural, electrical, and magnetic properties. The powder X-ray diffraction analysis reveals the single-phase nature of MgFe{sub 2}O{sub 4}. The field emission scanning electron microscopy image shows the nanosized grains. The magnetic study reveals the superparamagnetic behaviour of MgFe{sub 2}O{sub 4} with saturation magnetisation value of 14.57 emu/g. The blocking temperature is determined using low-temperature magnetic measurement which is equal to 139 K. Electrical study shows that the value of AC conductivity at 1 Hz is 1.12 × 10{sup − 8} S/cm at 303 K and increases with frequency as well as temperature. The complex impedance analysis shows the grain and grain boundary resistance equal to 6.23 × 10{sup 6} Ω and 1.27 × 10{sup 7} Ω, respectively. The complex electric modulus analysis confirms the presence of two relaxation processes in nanocrystalline MgFe{sub 2}O{sub 4}.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Ferromagnetic resonances in single-crystal yttrium iron garnet nanofilms fabricated by metal-organic decomposition

Tunable microwave and millimeter wave oscillators and bandpass filters with ultra-low phase noise play a critical role in electronic devices, including wireless communication, microelectronics, and quantum computing. Magnetic materials, such as yttrium iron garnet (YIG), possess ultra-low phase noise and a ferromagnetic resonance tunable up to tens of gigahertz. Here, we report structural and magnetic properties of single-crystal 60 and 130 nm-thick YIG films prepared by metal-organic decomposition epitaxy. These films, consisting of multiple homoepitaxially grown monolayers, are atomically flat and possess magnetic properties similar to those grown with liquid-phase epitaxy, pulsed laser deposition, and sputtering. Our approach does not involve expensive high-vacuum deposition systems and is a true low-cost alternative to current commercial techniques that have the potential to transform the industry.

Wang, Szu-Fan (Paul)↗
DOE OSTI2017

Emitting heterostructures with a bilayer InGaAs/GaAsSb/GaAs quantum well and a GaMnAs ferromagnetic layer

The radiative and magnetic properties of novel heterostructures with a bilayer InGaAs/GaAsSb/GaAs quantum well and a GaMnAs ferromagnetic layer are studied. The circular polarization of electroluminescent radiation is observed at temperatures from 10 to 160 K. The magnetic field dependences of the degree of circular polarization are nonlinear with a hysteresis loop at temperatures from 10 to 50 K, and they become linear at higher temperatures. The magnitude of polarization at the saturation magnetization of GaMnAs in the 2000 Oe field remains at the level of ~0.2%.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Oxygen Inhomogeneity and Reversibility in Single Crystal LaNiO{sub 3-{delta}}.

LaNiO 3− δ single crystals have been obtained via high pressure floating zone growth under 149 bar of oxygen pressure. We find a radial gradient in the magnetic properties of specimens extracted from the as-grown boule, which we correlate with the appearance of ordered oxygen vacancy structures. This radial oxygen inhomogeneity has been characterized systematically using a combination of magnetization and X-ray scattering measurements. We establish the presence of rhombohedral ( R 3 ¯ c ), oxygen stoichiometric specimens at the periphery of the boule and the presence of a dilute concentration of ordered oxygen-deficient orthorhombic La 2 Ni 2 O 5 in the center. Furthermore, we demonstrate that the as-grown, oxygen-deficient central regions of the crystal can be annealed under high oxygen pressure, without loss of crystallinity, into fully oxygenated LaNiO 3 , recovering magnetic properties that are characteristic of stoichiometric specimens from the exterior region of the crystal. Thus, single crystals of LaNiO 3− δ possess oxygen content that can be reversibly modified under oxidizing and reducing conditions.

crystal growth↗
DOE OSTI2017

A review: applications of the phase field method in predicting microstructure and property evolution of irradiated nuclear materials

Here, complex microstructure changes occur in nuclear fuel and structural materials due to the extreme environments of intense irradiation and high temperature. This paper evaluates the role of the phase field method in predicting the microstructure evolution of irradiated nuclear materials and the impact on their mechanical, thermal, and magnetic properties. The paper starts with an overview of the important physical mechanisms of defect evolution and the significant gaps in simulating microstructure evolution in irradiated nuclear materials. Then, the phase field method is introduced as a powerful and predictive tool and its applications to microstructure and property evolution in irradiated nuclear materials are reviewed. The review shows that (1) Phase field models can correctly describe important phenomena such as spatial-dependent generation, migration, and recombination of defects, radiation-induced dissolution, the Soret effect, strong interfacial energy anisotropy, and elastic interaction; (2) The phase field method can qualitatively and quantitatively simulate two-dimensional and three-dimensional microstructure evolution, including radiation-induced segregation, second phase nucleation, void migration, void and gas bubble superlattice formation, interstitial loop evolution, hydrate formation, and grain growth, and (3) The Phase field method correctly predicts the relationships between microstructures and properties. The final section is dedicated to a discussion of the strengths and limitations of the phase field method, as applied to irradiation effects in nuclear materials.

11 NUCLEAR FUEL CYCLE AND FUEL MATERIALS↗
DOE OSTI2016

Two-dimensional chiral asymmetry in unidirectional magnetic anisotropy structures

We investigate the symmetry-breaking effects of magnetic nanostructures that present unidirectional (one-fold) magnetic anisotropy. Angular and field dependent transport and magnetic properties have been studied in two different exchange-biased systems, i.e. ferromagnetic (FM)/ antiferromagnetic (AFM) bilayer and spin-valve structures. We experimentally show the direct relationships between the magnetoresistance (MR) response and the magnetization reversal pathways for any field value and direction. We demonstrate that even though the MR signals are related to different transport phenomena, namely anisotropic magnetoresistance (AMR) and giant magnetoresistance (GMR), chiral asymmetries are found around the magnetization hard-axis direction, in both cases originated from the one-fold symmetry of the interfacial exchange coupling. Our results indicate that the chiral asymmetry of transport and magnetic behaviors are intrinsic of systems with an unidirectional contribution.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2023

Revealing Site Occupancy in a Complex Oxide: Terbium Iron Garnet

Complex oxide films stabilized by epitaxial growth can exhibit large populations of point defects which have important effects on their properties. The site occupancy of pulsed laser-deposited epitaxial terbium iron garnet (TbIG) films with excess terbium (Tb) is analyzed, in which the terbium:iron (Tb:Fe)ratio is 0.86 compared to the stoichiometric value of 0.6. The magnetic properties of the TbIG are sensitive to site occupancy, exhibiting a higher compensation temperature (by 90 K) and a lower Curie temperature (by 40 K) than the bulk Tb 3 Fe 5 O 12 garnet. Data derived from X-ray core-level spectroscopy, magnetometry, and molecular field coefficient modeling are consistent with occupancy of the dodecahedral sites by Tb 3+ , the octahedral sites by Fe 3+ , Tb 3+ and vacancies, and the tetrahedral sites by Fe 3+ and vacancies. Energy dispersive X-ray spectroscopy in a scanning transmission electron microscope provides direct evidence of Tb Fe antisites. A small fraction of Fe 2+ is present, and oxygen vacancies are inferred to be present to maintain charge neutrality. In conclusion, variation of the site occupancies provides a path to considerable manipulation of the magnetic properties of epitaxial iron garnet films and other complex oxides, which readily accommodate stoichiometries not found in their bulk counterparts.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Probing Defects and Spin‐Phonon Coupling in CrSBr via Resonant Raman Scattering

Abstract Understanding the stability limitations and defect formation mechanisms in 2D magnets is essential for their utilization in spintronic and memory technologies. Here, defects in mono‐ to multilayer CrSBr are correlated with structural, vibrational, and magnetic properties. Resonant Raman scattering is used to reveal distinct vibrational defect signatures. In pristine CrSBr, it is shown that bromine atoms mediate vibrational interlayer coupling, allowing for distinguishing between surface and bulk defect modes. Environmental exposure is shown to cause drastic degradation in monolayers, with the formation of intralayer defects. This is in contrast to multilayers that predominantly show bromine surface defects. Through deliberate ion irradiation, the formation of defect modes is tuned: these are strongly polarized and resonantly enhanced, reflecting the quasi‐‐1D electronic character of CrSBr. Strikingly, pronounced signatures of spin‐phonon coupling of the intrinsic phonon modes and the ion beam‐induced defect modes are observed throughout the magnetic transition temperature. Overall, defect engineering of magnetic properties is possible, with resonant Raman spectroscopy serving as a direct fingerprint of magnetic phases and defects in CrSBr.

2D magnetic semiconductors↗
DOE OSTI2019

Effect of Annealing Treatment on Mechanical and Magnetic Softening Behaviors of Cold Rolled Interstitial-Free Steel

The recovery and recrystallization behaviors of low-carbon interstitial-free steel are investigated at different annealing temperatures (200-690 °C) through correlation between the changes in magnetic parameters (coercivity and r.m.s. voltage), hardness, tensile strength and high-angle grain boundary fractions (HAB). Magnetic parameters and tensile strength show a significant change within recovery region (200-500 °C), while the hardness variation is very minimal at this temperature region. On the other hand, the hardness is abruptly changed compared to magnetic properties at higher annealing temperature (550-640 °C). The grain boundary characteristics and microtexture evolution occurring at recrystallization regime are evaluated by orientation imaging microscopy (OIM) and orientation distribution function (ODF) through electron backscattered diffraction (EBSD). The increase in recrystallization fraction noticeably affects microtexture property, justifying with the strengthening of γ-fiber, weakening of α-fiber and disappearance of rotated cube component with increasing annealing temperatures.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Emergence of exchange bias and giant coercive field enhancement by internal magnetic frustration in La 0.67 Sr 0.33 MnO 3 thin films

We have studied the influence of controlled defects on the magnetic properties of La 0.67 Sr 0.33 MnO 3 (LSMO) thin films. We used 100 nm thick epitaxial LSMO films, which were grown on SrTiO 3 substrates and introduced stoichiometry changes and defects using oxygen ion irradiation through nanoporous alumina masks. Oxygen irradiation through the mask creates cascades of defects in spatially-modulated regions in the plane of the LSMO film. The magnetic properties of the samples were compared before and after the irradiation. We have found that irradiation reduces the ferromagnetic ordering temperature, decreases the total magnetization, enhances the coercivity, and induces exchange bias below 50 K. The coercivity enhancement is dramatically higher below 50 K and can be associated with exchange bias. These results can be explained by the formation of Mn-rich antiferromagnetic or ferrimagnetic phases within the bombarded regions that are exchange coupled to the non-irradiated - ferromagnetic host.

36 MATERIALS SCIENCE↗
DOE OSTI2018

An Investigation on Magnetic-Interacting Fe{sub 3}O{sub 4} Nanoparticles Prepared by Electrochemical Synthesis Method

Naked, polyvinylchloride (PVC)-coated, and polyethylene glycol (PEG)-coated Fe{sub 3}O{sub 4} nanoparticles (NPs) with an equivalent average particle size of 10 nm were prepared through an electrochemical synthesis method. The structural and magnetic properties were investigated systematically. The X-ray diffraction study coupled with the Rietveld refinement of XRD data showed that samples are crystallized in cubic spinel structure with space group referred to as Fd3m. The nature of DC magnetization versus field M (H) plot for sample resembles qualitatively with ferromagnetic (FM) systems. The AC-susceptibility data obtained at different frequencies confirmed the presence of a frequency-dependent freezing temperature. Based on the interparticle interaction strength and phenomenological models (Néel–Brown, Vogel–Fulcher, and critical slowing down), the magnetic dynamic behavior of nanoparticles was characterized. By fitting the experimental data with mentioned models, the possibility existence of superparamagnetic and a spin-glass state at low temperatures was proposed for the samples. Also, the obtained values from fitting performance showed a coating effect on interparticle interaction for PVC- and PEG-coated Fe{sub 3}O{sub 4} nanoparticles.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2017

NMR study of the paramagnetic state of low-dimensional magnets LiCu{sub 2}O{sub 2} and NaCu{sub 2}O{sub 2}

A comprehensive NMR study of the magnetic properties of single crystal LiCu{sub 2}O{sub 2} (LCO) and NaCu{sub 2}O{sub 2} (NCO) is carried out in the paramagnetic region of the compounds for various orientations of single crystals in an external magnetic field. The values of the electric-field gradient (EFG) tensor, as well as the dipole and transferred hyperfine magnetic fields for {sup 63,65}Cu, {sup 7}Li, and {sup 23}Na nuclei are determined. The results are compared with the data obtained in previous NMR studies of the magnetically ordered state of LCO/NCO cuprates.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Magnetism and magnetocrystalline anisotropy in single-layer PtSe{sub 2}: Interplay between strain and vacancy

The electronic and magnetic properties of the newly synthesized single-layer (1 L) transition-metal dichalcogenide (TMD) PtSe{sub 2} are studied by first-principles calculations. We find the strain or selenium vacancy (V{sub Se}) alone cannot induce the magnetism. However, an interplay between strain and V{sub Se} leads to the magnetism due to the breaking of Pt-Pt metallic bonds. Different from the case of 1 L-MoS{sub 2} with V{sub S}, the defective 1 L-PtSe{sub 2} has the spatially extended spin density, which is responsible for the obtained long range ferromagnetic coupling. Moreover, the 1 L-PtSe{sub 2} with V{sub Se} undergoes a spin reorientation transition from out-of-plane to in-plane magnetization, accompanying a maximum magnetocrystalline anisotropy energy of ∼9–10.6 meV/V{sub Se}. These results indicate the strain not only can effectively tune the magnetism but also can manipulate the magnetization direction of 1 L-TMDs.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Ab Initio Study of Magnetism in Nonmetal Adsorption on Arsenene Monolayer

The structural, electronic, and magnetic properties of adsorbed arsenene monolayer with a series of nonmetal atoms, including B, C, F, N, and O, are systematically investigated using first-principles calculations. Nonmagnetic behavior shows in the B-, F-, N-, and O-adsorbed systems. The magnetism has been observed in the case of C, which originated from the 2p electrons of C and its neighboring As 4p states. Meanwhile, these nonmagnetic elements can induce impurity channels around Fermi level, which reduce band gap of the systems. It implies that the B-, F-, N-, and O-adsorbed arsenene tune into narrow gap semiconductors without magnetic character. The X-adsorbed (X = B, C, F, N, and O) arsenene systems are promising candidates for spintronic devices in the future.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Investigation of Superparamagnetism in Microwave and Conventional Processed Mn{sub 0.5}Zn{sub 0.5}Fe{sub 2}O{sub 4} Nanoparticles

Nanoparticles of spinel cubic Mn{sub 0.5}Zn{sub 0.5}Fe{sub 2}O{sub 4} are first prepared by the coprecipitation method and then subjected to conventional solid-state sintering and microwave processing techniques. Particle sizes are estimated by field emission scanning electron microscopy (FESEM) to be in the nanometer (5–13 nm) range. Transmission electron microscopy (TEM) also supports the FESEM data. The magnetization measurement by vibration sample magnetometry of the conventionally sintered sample shows a paramagnetic nature at room temperature, a superparamagnetic behaviour at low temperature, and a ferromagnetic nature at even lower temperature. The blocking temperature is estimated to be nearly 110 K. Microwave-processed samples show a superparamagnetic nature even at room temperature. The Fe{sup 3+} cations are found at both the sites confirmed by X-ray photoelectron spectroscopy (XPS), are prepared by microwave processing, and have better magnetic properties as compared to the conventionally sintered particles.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2024

Fabrication of single-crystalline YFeO3 films with large antiferromagnetic domains

The antiferromagnetic orthoferrite YFeO3 possesses fascinating magnetic properties for spintronics, such as terahertz spin dynamics, ultrafast domain wall motion, and long magnon decay length. YFeO3 belongs to a special family of antiferromagnets that show an unusually strong non-trivial Kerr response due to its weak ferromagnetism. The highly stable antiferromagnetic domains without any spontaneous spin rotation transitions below the 645 K Néel temperature may be useful for nanoscale device applications. We report the successful fabrication of high-quality twinning-free (110)-oriented YFeO3 films by pulsed laser deposition. Detailed structural and magnetic characterization revealed that the crystal structure and magnetic properties of the YFeO3 films are comparable to bulk single crystals. We show that the spin rotation under high magnetic fields follows the two-sublattice approximation model. The film surface is atomically flat with step-terrace surface morphology. A longitudinal magneto-optic Kerr (MOKE) rotation of 10 mdeg was observed at room temperature, which is consistent with earlier reports on bulk single crystals. The in-plane anisotropy of the Kerr response corresponds to the obtained magnetic anisotropy from the SQUID measurement. The large MOKE signal enables the imaging of antiferromagnetic domains and their reversal. The domain size was found to be larger than 100 μm. These high-quality YFeO3 thin films facilitate the fabrication of antiferromagnetic spintronic devices and provide a convenient platform for studying various spin-related phenomena in thin films and at interfaces.

Physics↗