Search NASA⌕ Search

SEARCH · Search NASA

Results for “MAGNETIC PROPERTIES”

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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2023

Tuning the magnetic properties of the CrMnFeCoNi Cantor alloy

Magnetic properties of more than 20 Cantor alloy samples of varying composition were investigated over a temperature range of 5 K to 300 K and in fields of up to 70 kOe using magnetometry and muon spin relaxation. Two transitions are identified: a spin-glass-like transition that appears between 55K and 190K, depending on composition, and a ferrimagnetic transition that occurs at approximately 43K in multiple samples with widely varying compositions. The magnetic signatures at 43K are remarkably insensitive to chemical composition. A modified Curie-Weiss model was used to fit the susceptibility data and to extract the net effective magnetic moment for each sample. The resulting values for the net effective moment were either diminished with increasing Cr or Mn concentrations or enhanced with decreasing Fe, Co, or Ni concentrations. Beyond a sufficiently large effective moment, the magnetic ground state transitions from ferrimagnetism to ferromagnetism. The effective magnetic moments, together with the corresponding compositions, are used in a global linear regression analysis to extract element-specific effective magnetic moments, which are compared to the values obtained by ab initio based density functional theory calculations. Finally, these moments provide the information necessary to controllably tune the magnetic properties of Cantor alloy variants.

36 MATERIALS SCIENCE↗
DOE OSTI2019

The Crystal Structure, Raman Spectra, and Magnetic Properties of HoCrO{sub 3} Annealed in Different Atmospheres

The crystal structure, phonon Raman scattering, and magnetic properties of HoCrO{sub 3} were studied in a way of impacting the oxygen site by annealing treatment in argon and oxygen atmospheres. Although there are no dramatic changes in magnetic properties, a negative magnetization phenomenon below T{sub N} was observed in all prepared HoCrO{sub 3} samples and a certain of lattice distortion was affected due to the variation of Ho–O bond length and Cr–O–Cr bond angle and bond lengths. The Raman spectra exhibit an obvious shift of mode-related Ho ion instead of modes involved with Cr, which unconsciously leads to the variation of effective paramagnetic moments. The magnetic properties were systematically analyzed by Curie-Weiss and modified Curie-Weiss laws. The effective magnetic moment and symmetric and antisymmetric exchange interactions of J{sub e} and D were discussed. The reduced effective magnetic moments in HoCrO{sub 3} and annealed ones demonstrate possible vacancies of Ho and Cr, which was verified by elemental composition tested by energy-dispersive X-ray spectroscopy.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Multireference Ab Initio Studies of Magnetic Properties of Terbium-Based Single-Molecule Magnets

Here, we explore how different chemical environments influence magnetic properties of terbium(III) (Tb)-based single-molecule magnets (SMMs), using first-principles relativistic multireference methods. Recent experiments showed that Tb-based SMMs can have exceptionally large magnetic anisotropy and that they can be used for experimental realization of quantum information applications, with a judicious choice of chemical environment. Here, we perform complete active space self-consistent field calculations including relativistic spin–orbit interaction for representative Tb-based SMMs such as TbPc 2 and TbPcNc in three charge states. We calculate the low-energy electronic structure from which we compute the Tb crystal-field (CF) parameters and construct an effective pseudospin Hamiltonian. Our calculations show that the ligand type and fine points of molecular geometry do not affect the gap between the ground-state and first-excited doublets, whereas the latter varies weakly with oxidation number. On the other hand, higher-energy levels have a strong dependence on all these characteristics. For neutral TbPc 2 and TbPcNc molecules, the Tb magnetic moment and ligand spin are parallel to each other and the coupling strength between them does not depend much on the ligand type and details of the atomic structure. However, ligand distortion and molecular symmetry play a crucial role in transverse CF parameters which lead to tunnel splitting. The tunnel splitting induces quantum tunneling of magnetization by itself or by combining with other processes. Our results provide insights into the mechanisms of magnetization relaxation in the representative Tb-based SMMs.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Effect of Co on twin formation and magnetic properties of Sm(Fe,Ti,V) 12 alloys

Transferring the excellent intrinsic magnetic properties of SmFe 12 -based compounds to their extrinsic properties remains the main challenge in the development of high-performance SmFe12-based permanent magnets. Twin formation is one of the reasons for the inability to achieve high coercivity and remanence. Here we have shown that the addition of Co in Sm(Fe 1-x Co x ) 10–11 M 1–2 alloys, where M=Ti and V, leads to an increase in twin density. Microstructural characterizations revealed that the atomic arrangement in the twin boundary changes depending on the stabilizing element, which directly influences the local intrinsic magnetic properties. Theoretical investigations showed that the critical grain size at which twin formation can be hindered by grain size reduction decreases when the stabilizer changes from V to Ti. Furthermore, this study shows that the alloy composition influences not only the intrinsic magnetic properties but also the twin formation energy and its grain size dependence, crucial for the design of SmFe12-based permanent magnets.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of Fe Doping and O Vacancies on the Magnetic Properties of Rutile TiO{sub 2}

Magnetism sources of Fe doping and O vacancies, which coexist in the presence of rutile TiO{sub 2}, are controversial and require a resolution. The effects of Fe doping and point defect on the magnetism of rutile TiO{sub 2} were studied using geometry optimization and energy calculation based on the first principle generalized gradient approximation + U method (GGA+U) of density functional theory. Fe/Vo ratio is 1:1 in rutile TiO{sub 2}. The next closest distance between Fe and Vo is 0.04082 nm. The formation energy of the doping system is the smallest. This doping system has the highest stability. The coexistence of Fe doping and O vacancy achieved ferromagnetic long-range order. The different ratios of Fe/Vo are 1:1, 1:2, 2:1, and 2:2. The magnetic properties of the doping system are significantly different. At a ratio of 2:1, the magnetic moment is the largest among all doping systems. Moreover, the Curie temperature of the doping system can be higher than room temperature. These findings can obtain dilute magnetic semiconductors with potential application value. At a Fe/V{sub O} ratio of 2:2, the Ti{sub 14}Fe{sub 2}O{sub 30} system produces a half-metallic property of 100% electron spin polarizability. This is the most valuable application for designing and preparing novel spintronic injection source dilute magnetic semiconductors. The magnetic source is mainly mediated by the holes generated by Fe doping and O vacancy complexes, thereby causing the spin polarization double exchange effect on the electron of Ti–3d orbital atoms near the O vacancy, O–2p electron orbital, and Fe–3d electron orbital. This feature is consistent with the following theories: the mean field approximation and the double exchange mechanism theories.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

The Effects of Annealing after Equal Channel Angular Extrusion (ECAE) on Mechanical and Magnetic Properties of 49Fe-49Co-2V Alloy

Equal channel angular extrusion (ECAE) of 49Fe-49Co-2V, also known as Hiperco® 50A or Permendur-2V, greatly improves the strength and ductility of this alloy, while sacrificing soft magnetic performance. In this work, ECAE Hiperco specimens were subjected to post-ECAE annealing in order to improve soft magnetic properties. The microstructure, mechanical properties, and magnetic performance are summarized in this study. Annealing begins above 650°C and a steep decline in yield strength is observed for heat treatments between 700 and 840°C due to grain growth and the Hall-Petch effect, although some strength benefit is still observed in fully annealed ECAE material compared to conventionally processed bar. Soft magnetic properties were assessed through B-H hysteresis curves from which coercivity (Hc) values were extracted. Hc decreases rapidly with annealing above 650°C as well, i.e. improved soft magnetic behavior. The observed trend is attributed to annealing and grain growth in this temperature regime, which facilitates magnetic domain wall movement. The coercivity vs. grain size results generally follow the trend predicted in the literature. The magnetic behavior of annealed ECAE material compares favorably to conventional bar, possibly due to mild crystallographic texturing which enhances properties in the post-ECAE annealed material. Overall, this study highlights a definitive tradeoff between mechanical and magnetic properties brought about by post-ECAE annealing and grain growth.

annealing↗
DOE OSTI2021

Ironsand (Titanomagnetite-Titanohematite): Chemistry, Magnetic Properties and Direct Applications for Wireless Power Transfer

Ironsand is an abundant and inexpensive magnetic mineral resource. However, the magnetic properties of unprocessed ironsand are often inadequate for any practical applications. In this work, the applicability of ironsand for use as a component in a soft magnetic composite for large-scale inductive power transfer applications was investigated. After magnetic separation, the chemical, structural and magnetic properties of ironsand sourced from different locations were compared. Differences observed in the DC magnetic properties were consistent with changes in the chemical compositions obtained from X-ray Absorption Near-Edge Spectroscopy (XANES), which suggests varying the titanohematite to titanomagnetite content. Increased content in titanomagnetite and magnetic permeability correlated well with the total Fe content in the materials. The best-performing ironsand with the highest permeability and lowest core losses was used alongside Mn,Zn-Ferrite particles (ranging from ~100 μm to 2 mm) to fabricate toroid cores with varying magnetic material loading. It was shown that ironsand can be used to replace up to 15 wt.% of the magnetic materials with minimal impact on the composite magnetic performance, thus reducing the cost. Ironsand was also used as a supporting material in a single-rail wireless power transfer system, effectively increasing the power transfer, demonstrating potential applications to reduce flux leakage.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Microstructural evolutions, phase transformations and hard magnetic properties in polycrystalline Ce–Co–Fe–Cu alloys

This work focuses on systematic studies of Ce–Co based 1:5 permanent magnet alloys of CeCo 4.4-x Fe x Cu 0.6 and CeCo 3.9-x Fe x Cu 1.2 (x = 0, 0.3, 0.6, 0.9, 1.2, 1.8) by varying Co:Fe. The overarching aim of this manuscript is to elucidate the hard-magnetic properties through a better understanding of phase formation by the structural, microstructural, and magnetic properties in these materials. Improved mutual solubility of Fe in the 1:5 phase has been observed with an extended homogeneity range by Cu substitution. For both composition series, Fe contents of x ≤ 0.6 show a homogeneous microstructure with a single 1:5 phase and good magnetic properties. The composition region 0.6 < x ≤ 0.9 appears to be near the boundary of solubility and evolution of other phases. At x = 1.8, it is found that the homogeneous 1:5 phase and magnetic hardness deteriorated due to the evolution of secondary phases such as 2:17, 2:7, and Fe–Co. Furthermore, the addition of Fe improved both the magnetization and Curie temperature via increased effective exchange interactions, while an increase in Cu content enhanced coercivity.

33 ADVANCED PROPULSION SYSTEMS↗
DOE OSTI2019

Electronic and Magnetic Properties of Mn-doped and (Mn,C)-codoped w-AlN with the Presence of N Vacancy

In this paper, we discover the structural, electronic, and magnetic properties of Mn-doped (6.25 and 12.5%) and Mn-C-codoped wurtzite AlN with the presence of nitrogen vacancy. These properties have been investigated using density functional theory implemented in Quantum ESPRESSO package. AlN doped and codoped were optimized by using Broyden-Fletcher-Goldfarb-Shanno (BFGS) approximation. The electronic and magnetic properties are determined by the total and partial density of states. The presence of impurities and nitrogen vacancy induces magnetic properties, indicating that these materials are good candidates for electromagnetic and spintronics applications. Our results are in good agreement with experimental and other theoretical studies. We can conclude from this study that this material can be used as diluted magnetic semiconductors.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Electronic and Magnetic Properties of Os-Doped Rhodium Clusters: a Theoretical Study

The stability and electronic and magnetic properties of Rh{sub n}Os (n= 2–12) clusters in their most stable configurations were systematically studied by using density functional theory (DFT) at M06L/aug-cc-pVDZ level. Calculation of the second-order difference of energies and fragmentation energies exhibited that Rh{sub 3}Os, Rh{sub 5}Os, Rh{sub 7}Os, and Rh{sub 9}Os clusters are more stable than any other clusters. The calculated HOMO-LUMO energy gaps of the Rh{sub n}Os clusters are found to be in the range of 0.018 to 0.299 eV, implying that the metallic behavior can appear in these clusters. Accordingly, the Rh{sub n}Os clusters can be employed as heterogeneous nanocatalysts in many chemical reactions. The local Fukui function (f{sub k}{sup −}) has also been calculated, and the obtained results reveal that the highest f{sub k}{sup −} values are predicted for the Rh atoms. Therefore, the Rh atoms in the clusters are considered the most reactive sites that undergo reactions with electrophilic reagents. The analysis of the magnetic properties of the Rh{sub n}Os clusters shows that the total magnetic moment per atom of these clusters varies from 0.67 to 1.75 µ{sub B}/atom. And, the PDOS analysis reveals that the d orbitals play a crucial role for the magnetism of the Rh{sub n}Os clusters, and the contribution of the s and p orbitals is small.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Magnetic Properties of Fullerene–Thermally Exfoliated Graphite Composites Doped with Sodium

The magnetic properties (field range H = 0–50 kOe, temperature range T = 3–300 K), and structural features of a sodium-doped carbon composite material based on fullerene C{sub 60} and thermally exfoliated graphite (TEG) are studied. The material is obtained with different ratios of the components by sintering at a pressure of 7 GPa and T = 600°C, at which it is found that significant amorphization of the crystal lattice of the initial C{sub 60} occurs. The dia-, para-, and ferromagnetic components (M{sub D}, M{sub PM}, and M{sub FM}) were separated from the total magnetic moment of the samples under study. It is found that a sodium dopant has no effect on the magnetic properties of the composite. Analysis of the M{sub PM}(H) field dependences by using the Brillouin function for the fullerene-containing sample (i.e., without TEG) makes it possible to determine the quantum number of the total angular momentum of paramagnetic (PM) centers. Its value is found to be J = 1, which corresponds to elementary magnetic moment μ{sub PM} = 2μ{sub B} of a PM center. The concentration of PM centers is estimated at the level of N{sub PM} ≈ (2–5) × 10{sup 18} g{sup –1} for most samples, including the material without TEG. The introduction of TEG into the initial composition and an increase in its proportion in the composite leads to a strong increase in the magnetic moment, which is explained by an increase in both the J value and the concentration of PM centers.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Strain- and thickness-dependent magnetic properties of epitaxial La 0.67 Sr 0.33 CoO 3 /La 0.67 Sr 0.33 MnO 3 bilayers

Magnetic properties and interfacial phenomena of epitaxial perovskite oxides depend sensitively on parameters such as film thickness and strain state. In this work, epitaxial La0 .67 Sr 0.33 CoO 3 (LSCO)/La 0.67 Sr 0.33 MnO 3 (LSMO) bilayers were grown on NdGaO 3 (NGO) and LaAlO 3 (LAO) substrates with a fixed LSMO thickness of 6 nm, and LSCO thickness (t LSCO ) varying from 2 to 10 nm. Soft x-ray magnetic spectroscopy revealed that magnetically active Co 2+ ions that strongly coupled to the LSMO layer were observed below a critical t LSCO for bilayers grown on both substrates. On LAO substrates, this critical thickness was 2 nm, above which the formation of Co 2+ ions was quickly suppressed leaving only a soft LSCO layer with mixed valence Co 3+ /Co 4+ ions. The magnetic properties of both LSCO and LSMO layers displayed strong t LSCO dependence. This critical t LSCO increased to 4 nm on NGO substrates, and the magnetic properties of only the LSCO layer displayed t LSCO dependence. A non-magnetic layer characterized by Co 3+ ions and with a thickness below 2 nm exists at the LSCO/substrate interface for both substrates. Therefore, the results contribute to the understanding of interfacial exchange spring behavior needed for applications in next generation spintronic and magnetic memory devices.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Complex magnetic properties in the mixed 4 f - 5 d double perovskite iridates X 2 ZnIrO 6 ( X = Nd , Sm , Eu , Gd )

Here in this paper, we report on the synthesis and magnetic properties of a series of double perovskites Ln 2 ZnIrO 6 with Ln = Nd, Sm, Eu, Gd. These compounds present examples of the rare case of double perovskites (general formula A 2 BB'O6) with a magnetic 4ƒ-ion on the A site in combination with the strongly spin-orbit coupled 5d transition-metal ion Ir 4+ on the B sublattice. We discuss the impact of different rare earths on the macroscopic magnetic properties. Gd 2 ZnIrO 6 and Eu 2 ZnIrO 6 show ferrimagnetic or canted antiferromagnetic order below T N = 23 and 12 K, respectively. Sm 2 ZnIrO 6 orders antiferromagnetically at T N = 13 K. Nd 2 ZnIrO 6 exhibits more complex magnetic properties with a strong field dependence ranging from a two-step spin reorientation at μ 0 H = 0.01 T to an antiferromagnetic ground state at intermediate external fields to a spin-flop phase for 0H ≥ 4 T. This unique behavior suggests an interesting interplay between Nd 3+ and Ir 4+ . To further shed light on the relevant magnetic interaction, the zero-field magnetic ground state of Nd 2 ZnIrO 6 is examined via neutron powder diffraction. In general, the magnetic properties of Ln 2 ZnIrO 6 hint towards a substantial contribution of the rare-earth ions and a significant correlation between 5d and 4ƒ magnetism.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Magnetic Properties and Electronic Structure of Ni/C Multilayer Films

The magnetic properties of Ni/C multilayers were investigated using vibrating sample magnetometer and ferromagnetic resonance (FMR). Spin wave resonances were seen in FMR and the spin wave was found to be sustained through whole layers. The interlayer coupling constant was small pointing out a weak exchange coupling between Ni films through C spacers. The FMR linewidth, in parallel geometry, of the uniform mode decreases with the increase in Ni thickness from 30 to 300 Å which can be understood by considering interfacial effects. The magnetization decreases with decreasing Ni thickness due to the structural imperfections associated with the presence of Ni{sub 1−x}C{sub x} alloys at the interface. Density functional theory (DFT) has been performed to shed light on the decrease in magnetic moment at the interfaces.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2025

Effect of vanadium on phase composition and hard magnetic properties of as-solidified and heat-treated Sm–Fe–(Ti,V) alloys

Although the intrinsic magnetic properties of Ti-stabilized Sm(Fe,Co,Ti) 12 compounds exhibit potential of excellent rare-earth-lean permanent magnets, it has been much easier to realize large coercivities with the isostructural compounds stabilized by either V or by certain combinations of Ti and V. To elucidate the influence of V on the microstructure and magnetic properties, a series of Sm 8.1 Fe 78.4 (Ti 1-x V x ) 13.5 alloys was studied after arc-melting and annealing at 850–1000 °C. The alloys were found to fall into three groups. For x ≤ 0.2, solidification generates mostly the Sm(Fe,Ti,V) 12 phase, but annealing converts at least part of it into the non-magnetic Sm(Fe,Ti,V) 11 and the magnetically soft Sm 2 (Fe,Ti,V) 17 phases. For 0.2 < x < 0.6, the alloys solidify into a near-equilibrium mixture of the Sm(Fe,Ti,V) 12 , TiFe 2 and Sm-rich phases. For x ≥ 0.6, solidification generates large fractions of α-Fe solid solution and Sm-rich phases; an annealing step is necessary to complete the formation of Sm(Fe,Ti,V) 12 phase. Also, for x ≥ 0.6 the temperature below which the Sm(Fe,Ti,V) 12 phase is stable decreases with x, as does the fraction of this phase formed during solidification. Here, the differences between these three groups of alloys suggest different strategies for developing hard magnetic properties, with the likelihood of a success increasing with increasing x. For x ≥ 0.6, heat treatment alone is demonstrated to generate a microstructure of micron and submicron Sm(Fe,Ti 1-x V x ) 12 crystallites separated by a Sm-rich phase and exhibiting a coercivity with values up to 3.5 and 5.7 kOe for x = 0.8 and 1.0, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Study on Magnetic Properties and Degradability of Gas Atomization Fe-Based (Fe-Si-B-P) Amorphous Powder

Fe-based amorphous materials have attracted extensive attention in the application of organic pollutant degradation due to their excellent chemical properties. In this work, a novel Fe-based (Fe-Si-B-P) amorphous powder prepared by gas atomization is employed to decompose azo dyes for wastewater treatment. Its crystalline structure, distribution of particle size, and soft magnetic properties are characterized. The experimental results show that the Fe-based (Fe-Si-B-P) powder is amorphous morphology which might bring many benefits for decomposing organics in waste water. The particle size of the micro-sized spheroidal powder distributes mainly from 10 to 50 μm, and most are about 17~19 μm. The magnetic properties are also investigated. Its saturation magnetization (M{sub S}) and coercivity (H{sub C}) are, respectively, 55 emu/g and 19.6 Oe, which present superb soft magnetic properties. Finally, we studied the degradability of the Fe-based amorphous powder by decomposing the methylene blue in waste water, and the results show that 0.05-g Fe-based amorphous powder can completely degrade the 50 ml methylene blue solution with the concentration of 3 × 10{sup −5} M within 15 min in weak acidic environment, which shows great degradability for wastewater treatment.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Correlating structural, electronic, and magnetic properties of epitaxial VSe 2 thin films

The electronic and magnetic properties of transition metal dichalcogenides are known to be extremely sensitive to their structure. In this paper we study the effect of structure on the electronic and magnetic properties of mono- and bilayer VSe 2 films grown using molecular beam epitaxy. VSe 2 has recently attracted much attention due to reports of emergent ferromagnetism in the two-dimensional (2D) limit. To understand this compound, high-quality 1$\textit{T}$ and distorted 1$\textit{T}$ films were grown at temperatures of 200 °C and 450 °C, respectively, and studied using 4 K scanning tunneling microscopy and spectroscopy. The measured density of states and the charge density wave (CDW) patterns were compared to band structure and phonon dispersion calculations. Films in the 1$\textit{T}$ phase reveal different CDW patterns in the first layer compared to the second. Interestingly, we find the second layer of the 1$\textit{T}$ film shows a CDW pattern with 4$\textit{a}$ × 4$\textit{a}$ periodicity which is the 2D version of the bulk CDW observed in this compound. We report our phonon dispersion calculations confirm the presence of a soft phonon at the correct wave vector that leads to this CDW. In contrast, the first layer of distorted 1$\textit{T}$ phase films shows a strong stripe feature with varying periodicities, while the second layer displays no observable CDW pattern. Finally, we find that the monolayer 1$\textit{T}$ VSe 2 film is weakly ferromagnetic, with ~3.5 $μ_B$ per unit similar to previous reports.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Ab Initio Study of Electronic and Magnetic Properties of Germanene with Different Nonmagnetic Metal Adatoms

Electronic and magnetic properties of two-dimensional (2D) germanene (Ge) with five different adatoms have been analyzed and discussed by the DFT method. Different nonmagnetic metals adsorbed at different sites, on one hand, a magnetic moment is induced by Mg adatom in the germanene. On the other hand, the adsorptions of Al, Ga, Li, and Na show no magnetism. We further study the effect of strain on the magnetism in Mg-adsorbed germanene; we apply an isotropic tensile and compressive strain on the system. On the basis of our calculations, a tunable magnetism shows as the strain increases. The analysis of the PDOS shows that the s–p hybridization between Mg and Ge atoms results in such magnetic behavior. These magneticadsorbed germanene materials might show potential applications in the nanoscale devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗