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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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Magnetic properties of double perovskite L n 2 CoIrO 6 ( L n = Eu , Tb , Ho ) : Hetero-tri-spin 3 d - 5 d - 4 f systems

The field of double perovskites is now advancing to three magnetic elements on the A, B and B' sites. A series of iridium-based double perovskite compounds, Ln 2 CoIrO 6 (Ln = Eu, Tb, Ho), with three magnetic elements was synthesized as polycrystalline samples. The compounds crystalize in monoclinic structures with the space group P2 1 /n. Magnetic properties of these hetero-tri-spin 3 d-5 d-4 f systems were studied by magnetic susceptibility and field dependent magnetization in both DC and pulsed magnetic fields. All these compounds show ferrimagnetic transitions at temperatures T C above 100 K, which are attributable to antiferromagnetic coupling between Co 2+ and Ir 4+ spins. For Eu 2 CoIrO 6 , the magnetic properties are similar to those of La 2 CoIrO 6 . The Eu 3+ spins show Van Vleck paramagnetism, and do not significantly interact with transition-metal cations. In contrast, Tb 2 CoIrO 6 and Ho 2 CoIrO 6 reveal a second transition to antiferromagnetic order below a lower temperature T N . The temperature-induced ferrimagnetic-to-antiferromagnetic phase transition might be explained by a spin-reorientation transition. Moreover, a magnetic-field-induced spin-flop-like transition with a small hysteresis was observed below T N in these two compounds. The magnetic moments of all three compounds do not saturate up to 60 T at low temperatures. A moderate magnetocaloric effect was also observed in all three compounds. Our results should motivate further investigation of the spin configuration on single crystals of these iridium-based double perovskites.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Electronic Structure and Magnetic Properties of Cobalt-Doped Nonstoichiometric Rutile Thin Films

The coherent potential method has been applied for the investigation of Co substitutional doping influence on the spectral and magnetic properties of TiO{sub 2} rutile (100) surface. Both stoichiometric and nonstoichiometric oxygen compositions have been considered. For the stoichiometric case, the energy spectrum corresponds to half-metallic ferromagnet. The Co ions are in 2 + formal oxidation state with a spin magnetic moment of 0.8 μ{sub B}. The presence of oxygen vacancies makes the surface insulating and increases the Co spin magnetic moment value.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Mn-substituted cerium oxide nanostructures and their magnetic properties

Highlights: • Mn{sub x}Ce{sub 1-x}O{sub 2} (0.1 ≤ x ≤ 0.5) nanostructures were prepared by one step microwave refluxing method. • The saturation magnetization values for the samples rose with increased Mn content. • The oxygen vacancies inherently played crucial role in increasing the magnetization values. - Abstract: In this study, we report the magnetic properties of nanostructured Mn{sub x}Ce{sub 1-x}O{sub 2} (0 0.1 ≤ x ≤ 0.5) materials, synthesized via microwave refluxing technique. Phase purity of the samples was investigated using the structural characterization techniques such as X-ray diffraction (XRD) and transmission electron microscopy (TEM). These analyses indicated the substitution of Ce-ions with Mn-ions in the lattice. The progressive increase in the oxygen vacancies with increased dopant concentration was demonstrated by Raman, UV–vis and photoluminescence spectroscopic studies. X-ray photoelectron spectroscopy analysis further supported the presence of Mn{sup 2+}, Ce{sup 3+} and Ce{sup 4+} ions as well as oxygen vacancies in the samples. The Mn substituted CeO{sub 2} nanostructures were found to exhibit room temperature ferromagnetism (RTFM). There was a continuous improvement in the saturation magnetization (M{sub S}) values with increased Mn concentration. This might be due to the prevalence of surface oxygen vacancies and the systematic rise in their concentration with increased dopant content.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2022

Magnetic properties of equiatomic CrMnFeCoNi

Magnetic, specific heat, and structural properties of the equiatomic Cantor alloy system are reported for temperatures between 5 and 300 K, and up to fields of 70 kOe. Here magnetization measurements performed on as-cast, annealed, and cold-worked samples reveal a strong processing history dependence and that high-temperature annealing after cold working does not restore the alloy to a “pristine” state. Measurements on known precipitates show that the two transitions, detected at 43 and 85 K, are intrinsic to the Cantor alloy and not the result of an impurity phase. Experimental and ab initio density functional theory computational results suggest that these transitions are a weak ferrimagnetic transition and a spin-glass-like transition, respectively, and magnetic and specific heat measurements provide evidence of significant Stoner enhancement and electron-electron interactions within the material.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Bacterial Ferrihydrite Nanoparticles: Preparation, Magnetic Properties, and Application in Medicine

Nanoparticles of antiferromagnetically ordered materials acquire the uncompensated magnetic moment caused by defects and surface effects. A bright example of such a nano-antiferromagnet is nanoferrihydrite consisting of particles 2–5 nm in size, the magnetic moment of which amounts to hundreds of Bohr magnetons per particle. We present a brief review of the studies on magnetic properties of ferrihydrite produced by bacteria. Special attention is focused on the aspects of possible biomedical applications of this material, i.e., the particle elimination, toxicity, and possible use for targeted drug delivery.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2018

Structure and Magnetic Properties of Nanowires of Iron Group Metals Produced by Matrix Synthesis

Abstract—Samples of arrays of nanowires are produced from iron, iron–cobalt and iron–nickel alloys via matrix synthesis based on polymer track membranes with pore diameters ranging from 30 to 300 nm. The influence of stress and pore diameter on the galvanic process and structure of nanowires is studied. The arrays of nanowires are examined by microscopy and X-ray diffraction. The magnetic properties are inspected via magnetometry and Mössbauer spectroscopy. The angular dependences of hysteresis loop shape are obtained and comprehensively discussed. As shown, decreasing the growth stress and/or increasing the pore diameter make the Mössbauer spectra of nanowires similar to those of bulk materials. Furthermore, the higher the growth stress is, the larger is the coercive force of nanowires. For the studied species of nanomaterials, the ability to control the magnetic properties during the synthesis is shown, as well.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Effect of the Boron Content on the Amorphization Process and Magnetic Properties of the Mechanically Alloyed Fe{sub 92−x}Nb{sub 8}B{sub x} Powders

The effect of the B content on the microstructural, structural, and magnetic properties of partially amorphous Fe{sub 92−x}Nb{sub 8}B{sub x} (x = 5, 10, 15, and 20) alloys has been investigated by means of scanning electron microscopy, X-ray diffraction, high and low-temperature extraction-type magnetometers. The XRD results reveal the formation of a nanocomposite structure where nanocrystalline bcc α-Fe and Fe{sub 2}B phases are embedded into an amorphous matrix. The FeB boride is observed for higher boron contents (x = 15 and 20), and the crystallite sizes are in the range of 7–24 nm. As the B content increases, the amorphous phase-relative proportion and coercivity increase, whereas the saturation magnetization decreases. An important magnetic hardening occurs by lowering the temperature from 400 to 5 K for x = 20% B. The variation of the Curie temperature can be attributed to the heterogeneity of the amorphous matrix.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Magnetic Properties and Mössbauer Investigations of La{sub 0.67}Sr{sub 0.33}Fe{sub x}Mn{sub 1−x}O{sub 3} (x = 0 and 0.5) Perovskites

We report magnetic phase separation in pure La{sub 0.67}Sr{sub 0.33}Fe{sub x}Mn{sub 1−x}O{sub 3} (x = 0 and 0.5) ceramic samples. Rhombohedral crystal structures obtained with R3C space group show no significant changes in the lattice structures due to the close values of ionic radii of Fe{sup 3+} and Mn{sup 3+} ions. However, significant changes occur in the magnetic properties due to competing ferromagnetic (FM) and antiferromagnetic (AFM) interactions because of the presence of Fe{sup 3+} substitution. The FM double exchange interactions (DE) (Mn{sup 3+}–O–Mn{sup 4+}) appears suppressed by AFM superexchange interactions (Fe{sup 3+}–O–Mn{sup 4+}, Fe{sup 3+}–O–Fe{sup 3+}, Mn{sup 4+}–O–Mn{sup 4+}). The saturation magnetization for x = 0 has the highest value of approximately 80 emu/g at 2 K, which dropped significantly to approximately 5 emu/g at 2 K for the x = 0.5 sample. The coercivity (H{sub c}) for x = 0.5 increased from 161 Oe at 300 K to 786 Oe at 2 K compared with that of x = 0 which varied from 110 to 150 Oe. A value of H{sub c}(0) = 1.5 ± 0.04 kOe was extrapolated from the model fit to the temperature dependence of H{sub c}. The temperature-dependent {sup 57}Fe Mössbauer spectroscopy measurements show the presence of Fe in two different environments that have an AFM Fe{sup 3+}–O–Mn{sup 4+} and Fe{sup 3+/2+}–O–Fe{sup 3+/2+} coordination. The unequal fraction population of Fe ions at both AFM environments seems to increase the exchange bias effect.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2020

Control of magnetic properties of MnBi 2 Te 4 using a van der Waals ferroelectric III 2 -VI 3 film and biaxial strain

Using the first-principles calculations, we systematically investigated magnetic properties of a MnBi 2 Te 4 (MBT) monolayer in contact with III 2 -VI 3 two-dimensional ferroelectric substrates. As the electric polarization in the ferroelectric films is switched, a semiconductor to half-metal transition occurs in MBT, and its magnetic easy axis in several cases reorients. As an example, the Curie temperature of MBT/In 2 Se 3 can be enhanced to 21.5 or 32 K under the influence of electric polarization and biaxial strain, much higher than that of the pristine MBT monolayer, which is 14.5 K in our calculations. Our results in this work suggest effective ways to tune magnetic properties of MBT and provide useful insights for the further development of these important van der Waals functional materials.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Effect of the Laser Scan Rate on the Microstructure, Magnetic Properties, and Microhardness of Selective Laser-Melted FeSiB

FeSiB alloys have been fabricated by selective laser melting (SLM) using a laser scan rate of 0.1–1.5 m/s, laser power of 90 W, scan line spacing of 40 μ m, and layer thickness of 50 μ m. X-ray diffraction, scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy, atomic force microscopy, profilometer, microdurometer, and vibrating sample magnetometer have been used to investigate the structural, microstructural, roughness, microhardness, and magnetic property changes during the laser melting process. The produced samples exhibit a nanocomposite structure consisting of nanocrystalline α-Fe{sub 0.95}Si{sub 0.05} and Fe{sub 2}B phases embedded into an amorphous ε-FeSi-type matrix. The selective laser-melted samples show high density, low surface roughness, higher microhardness values (1654–2273 Hv), and soft magnetic properties (M{sub s} = 188.6–199 emu/g and H{sub c} = 43.8–73 Oe).

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Role of Ni concentration on structural and magnetic properties of inverse spinel Ferrite

Highlights: • Ni doped Co{sub 1-x}Mn{sub x}Fe{sub 2}O{sub 4} (0≤x≤0.1) nanoparticles have been synthesized with an average particle size in the range 15–20 nm. • Lattice parameter decreases with increase in Ni concentration in CoFe{sub 2}O{sub 4} nanoparticles. • XRD and FTIR analysis confirmed the formation of cubic spinel ferrite structure. • Room temperature and low temperature magnetic properties of described system have been measured. - Abstract: In present work, Nickel (Ni) substituted Mn-Co ferrite nanoparticles, with doping content varying from 0 to 0.1, have been synthesized. The inverse spinel structure of doped cobalt ferrite has been claimed by X-ray diffractometer with average particle size of 20 nm. The decrease in lattice parameter and increase in X-ray density has been found with increase in Ni concentration in ferrite structure. Fourier transform infrared spectroscopy analysis showed two vibrational frequency bands (υ{sub 1} and υ{sub 2}) for octahedral and tetrahedral sites depicting the formation of spinel ferrite. In addition, Transmission electron microscopy analyses were carried out to investigate particle size, which indicates that TEM and XRD analyses are in agreement. Magnetic analyses depict that coercivity value increases from 635 Oe to 841 Oe in Ni doped Mn-Co ferrite. Exchange interactions between Ni and Mn{sub 0.2}Co{sub 0.8-x}Fe{sub 2}O{sub 4} result for enlargement in coercivity and shift in hysteresis loop towards positive direction along the field axis. The increment in magnetic coercive field and exchange bias has been observed as temperature decreases. Enhanced magnetic properties at low temperature are attributed to magneto-crystalline anisotropy and surface effects.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Semihard magnetic properties of TiFe 2.5 iron-rich Laves phase and the effect of 4d- and 5d-element-substitutions for Ti

Rare-earth-free compounds exhibiting modest intrinsic hard magnetic properties may still yield viable permanent magnets if their constituent elements are abundant and inexpensive, and the properties are at least comparable to those of the hard ferrites. In this study, one such compound, the off-stoichiometric TiFe 2.5 Laves phase with the hexagonal C14 crystal structure, was found to exhibit – in addition to the already known room-temperature ferromagnetism – a uniaxial, albeit weak, magnetic anisotropy. With a Curie temperature of 422 K, saturation magnetization of 55.3 Am 2 /kg and magnetic hardness parameter of 0.97 this semihard compound is just below the threshold for being of interest for the development into permanent magnets. Replacing a small fraction of Ti with the 4d Nb and Mo or with the 5d Ta or W increases the anisotropy field, but only below room temperature. Replacing Ti with Zr or Hf increases the Curie temperature and leads to a spin reorientation below 200 K. All these substitutions, as well as combined (Zr,W) and (Nb,W) substitutions, fail to improve the room-temperature intrinsic hard magnetic properties of the Fe-rich Laves phase. Furthermore, an attempt to develop a room-temperature coercivity through high-energy ball-milling yielded a value of 0.026 T, an unusually small 2.9% fraction of the anisotropy field. Here, defects inherent in the C14 crystal lattice may be responsible for the underperformance.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Magnetic Properties of Ru-Doped Nd{sub 0.67}Sr{sub 0.33}Mn{sub 1−x}Ru{sub x}O{sub 3} (0 ≤ x ≤ 0.10) Manganites

The structural and magnetic properties of polycrystalline Nd{sub 0.67}Sr{sub 0.33}Mn{sub 1−x}Ru{sub x}O{sub 3} (x = 0.00 and 0.10) samples have been studied with the substitution of Ru at Mn site. The samples have orthorhombic crystal structure determined by room-temperature X-ray diffraction and Rietvield analysis. On Ru doping at Mn site, a change in its symmetry space group is observed. The increase in Ru content significantly affects the Curie temperature (T{sub c}). The double-exchange mechanism is suppressed with Ru doping affecting the Mn{sup 3+}–O{sup 2−}–Mn{sup 4+} ion network. Paramagnetic regime of samples in magnetization-temperature graph is fitted and analyzed with Curie-Weiss law. The magnetization versus applied magnetic field measurements show that the samples exhibit ferromagnetic behavior at lower temperatures and paramagnetic behavior at room temperature with negligible hysteresis loop and low coercive field.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Structural, Electronic, Optical, and Magnetic Properties of Fe{sub 3}Al Alloys

We have investigated the structural, optical, and magnetic properties of D0{sub 3} Fe{sub 3}Al alloys along with the electronic structure calculations. X-ray diffraction patterns confirm the single-phase cubic structure with a symmetry for the arc-melted samples. In the field dependence of magnetic data, ferromagnetic behavior is witnessed down to 2 K from room temperature. The electronic structure calculation corroborates the experimental observation of ferromagnetism in this alloy. Further, optical conductivity data in excellent agreement with the electronic structure calculations confirmed that electronic transitions are predominant by the 3d states of Fe.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Synthesis of the Orthorhombic Dy{sub 1−x}Ho{sub x}MnO{sub 3} Single Crystals and Study of Their Magnetic Properties

In this report, we prepared for the first time the orthorhombic Dy{sub 1−x}Ho{sub x}MnO{sub 3} single crystals with x = 0, 0.1, 0.2, 0.3, and 0.4 using the flux technique. The post-growth processing and chemical and structural characterization of the synthesized samples were performed. Also, we examined the samples obtained by their magnetic properties and the magnetic anisotropy in wide ranges of temperatures and magnetic fields.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

The application of macroscopic flakes for Fe-6.5%Si bulk magnetics with superior magnetic properties

Silicon steel is the most popular crystalline soft magnetic material for motor and transformer applications. The material must be in thin thickness to reduce the eddy current loss. Conventional thin steel sheet manufacturing process starts with cast slab, followed by a series of hot/cold roll process. For transformer, thin sheet is wrapped to form the core; for motor, the sheet is stamped, coated, heat treated, and stacked to form stator/rotor. This process requires the steel to possess sufficient ductility. For Si steel, increasing Si content will improve its electrical and magnetic properties, but it will also lead to embrittlement with 3.5% Si as the limit for the conventional manufacturing processes. Despite poor mechanical properties, high Si steel, especially the one with 6.5% Si, is gaining more attention due to its lower iron loss, higher permeability, and near zero magnetostriction. To address the brittleness problem of the 6.5% Si steel, we developed a novel process, using rapid solidification to prepare thin flakes with high ductility, then using hot press to consolidate the flakes into near net shape bulk sample. The obtained Fe-6.5%Si sample with 0.2 mm thickness exhibits an iron loss of 7.2 W/kg at 400Hz and magnetic flux density of 1 Tesla, and a maximum permeability of 28,400. In addition, various coating materials and processes were investigated as inter-flake insulators for their effect on reducing the eddy current losses for thicker configuration.

Fe-6.5%Si Steel↗
DOE OSTI2024

Intrinsic and hard magnetic properties of (Sm 1-x R x )-Fe-Co-V alloys (R = Gd, Zr, and Y)

SmFe 12 -based compounds with the ThMn 12 -type structure have a great potential as future rare-earth-lean permanent magnets. However, their reliance on stabilizing non-magnetic elements has impeded practical applications. Therefore, elements such as Gd, Y, and Zr have gained popularity as candidates to minimize the need for stabilizing elements by reducing the formation energy of the ThMn 12 (1:12) phase. Here, this study examines the effect of Gd, Y, and Zr on the intrinsic and hard magnetic properties in (Sm 1-x R x ) 1.2 Fe 8.4 Co 2.1 V 1.5 (or with nominal composition of (Sm 1-x R x ) 9.1 Fe 63.6 Co 15.9 V 11.4 ) with a single 1:12 phase for 0 ≤ x ≤ 0.3. Notably, samples substituted with Gd exhibit an enhanced temperature dependence of the magnetic properties.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Low Temperature and Surfactant-Free Hydrothermal Synthesis of CoNi Nanoparticles: Structure, Microstructure, and Magnetic Properties

We report on the synthesis of Co{sub 30}Ni{sub 70} nanoparticles using hydrothermal method at low temperatures and short times (100 °C, 2 h) without any surfactant or external magnetic field. The effect of NaOH concentration on the crystal structure, microstructure, and magnetic properties of CoNi samples has been investigated by x-ray diffraction (XRD), scanning (SEM) and high-resolution transmission (HRTEM) electron microscopy, and vibrating sample magnetometry (VSM). From the Rietveld refinement of x-ray powder diffraction patterns, we have evidenced the coexistence of two phases with face-centered cubic (FCC) and hexagonal (HCP) crystal structures, being 12 nm and 3 nm, respectively, the values for the mean grain size of both phases. SEM images show that the basic microstructure is composed of quasi-spheres and a chain-like morphology appears with increasing the amount of NaOH. HRTEM images evidence the formation of such chains, and confirm the coexistence of FCC and HCP phases. The magnetic hysteresis loops show a clear dependence of the coercivity on the particle morphology indicating the role played by the magnetic shape anisotropy.

77 NANOSCIENCE AND NANOTECHNOLOGY↗