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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 235 records · Page 13
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

The formation and structure of mechano-synthesized nanocrystalline Sr{sub 3}Fe{sub 2}O{sub 6.4}: XRD Rietveld, Mössabuer and XPS analyses

Highlights: • The formation of mechano-synthesized nanocrystalline Sr{sub 3}Fe{sub 2}O{sub 7−δ} is investigated. • Pre-milling the reactants substantially lowers the formation temperature. • The core and surface structures were studied. • XRD and {sup 57}Fe Mössbauer spectroscopic analyses indicate the δ-value to be 0.60. • XPS shows a complex surface structure for the mechanosynthesized Sr{sub 3}Fe{sub 2}O{sub 7−δ} nanoparticles. - Abstract: The influence of ball milling and subsequent sintering of a 3:1 molar mixture of SrCO{sub 3} and α-Fe{sub 2}O{sub 3} on the formation of Sr{sub 3}Fe{sub 2}O{sub 7−δ} double perovskite is investigated with different analytical techniques. Milling the mixture for 110 h leads to the formation of SrCO{sub 3}-α-Fe{sub 2}O{sub 3} nanocomposites and the structural deformation of α-Fe{sub 2}O{sub 3} via the incorporation of Sr{sup 2+} ions. Subsequent sintering of the pre-milled reactants’ mixture has led to the partial formation of an SrFeO{sub 3} perovskite-related phase in the temperature range 400–600 °C. This was followed by the progressive development of an Sr{sub 3}Fe{sub 2}O{sub 7−δ} phase that continued to increase with increasing sintering temperature until a single-phased nanocrystalline Sr{sub 3}Fe{sub 2}O{sub 7−δ} phase was attained at 950 °C (12 h). This temperature is ∼350 °C lower than the temperature at which the material is prepared conventionally using the ceramic method. The evolution of different structural phases during the reaction process is discussed. Rietveld refinement of the X-ray diffraction data shows a value of 0.60 for the oxygen deficiency δ, in consistency with the Fe{sup 3+}/Fe{sup 4+} ratio derived from the {sup 57}Fe Mössbauer data recorded at both 300 K and 78 K. The Mössbauer data suggests that the Sr{sub 3}Fe{sub 2}O{sub 6.4} nanoparticles are superparamagnetic with blocking temperatures below 78 K. The surfaces of the Sr{sub 3}Fe{sub 2}O{sub 6.4} nanoparticles were shown to have a complex structure and composition relative to those of their cores with traces of SrCO{sub 3}, SrO and SrFeO{sub 3−δ} being detected.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Synthesis, characterization and magnetic property of maghemite (γ-Fe{sub 2}O{sub 3}) nanoparticles and their protective coating with pepsin for bio-functionalization

Highlights: • Maghemite nanoparticles were prepared by a modified co-precipitation method. • Nanoparticles were then successfully coated with pepsin for bio-functionlization. • XRD and Mössbauer spectra confirmed the maghemite phase of the nanoparticles. • Magnetic data were analysed to evaluate particle size, anisotropy etc. - Abstract: Maghemite nanoparticles (γ-Fe{sub 2}O{sub 3}) are prepared by co-precipitation method. To obtain bio-functionalized magnetic nanoparticles for magnetically controlled drug delivery, the prepared nanoparticles are successfully coated with pepsin, a bio-compatible polymer and digestive enzyme. Crystallographic phase of the nanoparticles is confirmed by X-ray diffractograms (XRD), high resolution transmission electron microscopy (HRTEM) and {sup 57}Fe Mössbauer spectrometry. The average size of nanoparticles/nanocrystallites is estimated from the (3 1 1) peak of the XRD pattern using Debye–Scherrer formula. Results of HRTEM of coated and bare samples are in good agreement with those extracted from the XRD analysis. The dynamic magnetic properties are observed and different quantities viz., coercive field, magnetization, remanence, hysteresis losses etc., are estimated, which confirmed the presence of superparamagnetic relaxation of nanoparticles. Mössbauer spectra of the samples recorded at both 300 and 77 K, confirmed that the majority of particles are maghemite together with a very small fraction of magnetite nanoparticles.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Structural, magnetic, dielectric and magneto-dielectric properties of (BaTiO3)0.70(Li0.3Zn0.4Fe2.3O4)0.30

Highlights: Microcrystals of BaTiO{sub 3} is incorporated in Li{sub 0.3}Zn{sub 0.4}Fe{sub 2.3}O{sub 4} using sol-gel method. Crystallographic phase and morphology of the composite is investigated. Magnetic ordering originates from the ferrimagnetic matrix of the composite. The dielectric behaviour is originated from the BaTiO{sub 3} particles in the composite. The composite shows strong magneto-electric property, useful for application. - Abstract: Structural, magnetic, dielectric and magneto-dielectric properties of (BaTiO{sub 3}){sub 0.70}(Li{sub 0.3}Zn{sub 0.4}Fe{sub 2.3}O{sub 4}){sub 0.30} [BTO-LZFO] composite are studied. To prepare the composite, microcrystals of BaTiO{sub 3} [BTO] prepared in solid-state reaction are taken along with the precursors of Li{sub 0.3}Zn{sub 0.4}Fe{sub 2.3}O{sub 4} [LZFO], prepared in sol-gel route. X-ray diffraction (XRD) study confirms the phase purity of the composite sample. High-resolution transmission electron microscopy also confirms the formation of the composite state. Analysis of magnetic data confirms the ferrimagnetic nature of the sample along with a fraction of superparamagnetic particles. The ferrimagnetism is explained by Néels’ two-sublattice model. The dielectric spectrum of the sample follows the Cole-Cole relaxation. Interestingly, the ferroelectric and dielectric behaviours of BTO are retained in the composite state of BTO-LZFO, though the magnetization is enhanced drastically. This enhanced magnetic property along with the ferroelectricity and strong magneto-dielectric coupling in the composite state confirms that BTO-LZFO can be used as a multiferroic material in different electronic devices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2010

Size selected synthesis of CoFe{sub 2}O{sub 4} nanoparticles prepared in a chitosan matrix

In this paper we report the synthesis and magnetic properties of CoFe{sub 2}O{sub 4} nanoparticles. The nanoparticles with sizes ranging from 6 to 20 nm were prepared in a chitosan matrix. Size selection was achieved by introducing a nonionic surfactant Tween-X, where X={l_brace}20, 60, 80, and 85{r_brace}. Aqueous dispersions of Tween-X show micelles with increasing hydrodynamic sizes as X increases. Moessbauer spectroscopy measurements at 300 K show superparamagnetic behavior for the small particles, changing gradually to a blocked magnetic regime as the particle size increases. Magnetization measurements at 300 K show increasing values for the ratio M{sub r}/M{sub Hmax} and coercive fields (H{sub c}).

36 MATERIALS SCIENCE↗
DOE OSTI2010

Magnetoresistance and transport properties of CoFeB/MgO granular systems

Magnetoresistance and transport properties of ultrathin multilayers of CoFeB/MgO prepared by rf and dc magnetron sputtering were studied in the temperature range between 15 and 330 K. Due to the magnetic softness of CoFeB, this system offers a potentially high magnetoresistance at comparably low magnetic fields. At fixed MgO thickness of 0.7 nm, it undergoes a crossover from a granular to a multilayered structure with increasing thickness of CoFeB and metallic conduction is reached at around 0.8 nm. In the granular state, a ferromagnetic to superparamagnetic phase transition was observed at 130 K. Different charge transport phenomena were identified at different temperatures. A sharp increase in the magnetoresistance at low temperature can be attributed to higher order tunneling processes. By proper annealing procedures, an enhanced magnetoresistance of around 6% at room temperature and 14% at low temperature as well as an increase in the resistivity have been achieved.

36 MATERIALS SCIENCE↗
DOE OSTI2010

Preparation and Properties of FeCo Nanoparticles

Fe-Co nanoparticles were prepared from the binary Fe-Co oxalate. The formation of FeCo metallic phase begun at 290 deg. C as determined from the X-ray diffraction patterns recorded during heating of the oxalate sample in hydrogen atmosphere. The reduction finished at 500 deg. C by formation of bcc FeCo phase with a mean particle size of about 50 nm. Analysis of the Moessbauer spectra shows that the ferromagnetic FeCo phase is represented by two sextets corresponding to interiors and surfaces of the nanoparticles. In addition, a weak paramagnetic component, represented by the doublet, was observed which was ascribed to fine particles in a superparamagnetic state. TEM images have shown conglomerates of particles with the composition of about 50 at. % Fe and 50 at. % Co.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2010

Single particle detection: Phase control in submicron Hall sensors

We present a phase-sensitive ac-dc Hall magnetometry method which allows a clear and reliable separation of real and parasitic magnetic signals of a very small magnitude. High-sensitivity semiconductor-based Hall crosses are generally accepted as a preferential solution for non-invasive detection of superparamagnetic nanobeads used in molecular biology, nanomedicine, and nanochemistry. However, detection of such small beads is often hindered by inductive pick-up and other spurious signals. The present work demonstrates an unambiguous experimental route for detection of small magnetic moments and provides a simple theoretical background for it. The reliability of the method has been tested for a variety of InSb Hall sensors in the range 600 nm-5 {mu}m. Complete characterization of empty devices, involving Hall coefficients and noise measurements, has been performed and detection of a single FePt bead with diameter of 140 nm and magnetic moment of {mu}{approx_equal}10{sup 8} {mu}{sub B} has been achieved with a 600 nm-wide sensor.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2010

Origin of ferromagnetism in self-assembled Ga{sub 1-x}Mn{sub x}As quantum dots grown on Si

Self-assembled Ga{sub 1-x}Mn{sub x}As magnetic semiconductor quantum dots have been grown on Si (001) substrates using droplet epitaxy by molecular-beam epitaxy. Structural characterization reveals that these dots possess a zinc-blende lattice. The Ga{sub 1-x}Mn{sub x}As quantum dots with 8% Mn content are ferromagnetically soft and slightly anisotropic at low temperature, and show the superparamagnetic behavior with a blocking temperature of 20 K in the in-plane direction. Moreover, the results of x-ray absorption near edge structure provide direct evidences for the substitutional Mn{sup 2+} ion with a half-filled d{sup 5} configuration for the Ga site, suggesting the hole-mediated ferromagnetism in zero-dimensional Ga{sub 1-x}Mn{sub x}As quantum dots.

36 MATERIALS SCIENCE↗
DOE OSTI2010

Synthesis, Characterization, and Preliminary Investigation of Cell Interaction of Magnetic Nanoparticles with Catechol-Containing Shells

Superparamagnetic iron oxide cores were synthesized by co-precipitation of Fe(II) and Fe(III) salts and subsequently stabilized by coating with different catechols (levodopa, dopamine, hydrocaffeic acid, dopamine-containing carboxymethyl dextran) known to act as high-affinity, bidentate ligands for Fe(III). The prepared stable magnetic fluids were characterized with regard to their chemical composition (content of iron and shell material, Fe(II)/Fe(III) ratio) and their physical properties (size, surface charge, magnetic parameters). The nanoparticles showed no or only slight cytotoxic effects within 1 and 4 days of incubation with 3T3 fibroblast cells. Preliminary experiments were performed to study the interaction of the prepared nanoparticles with human MCF-7 breast cancer cells and leukocytes. An intense interaction of the MCF-7 cells with these particles was found whereas the leukocytes showed a lower tendency of interaction. Based on these finding, the novel magnetic nanoparticles possess the potential for use in depletion of tumor cells from peripheral blood.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2010

Magnetite Nanoparticles Coated with Rifampicin and Chlortetracycline for Drug Delivery Applications

Four types of biocompatible magnetic fluids based on superparamagnetic nanoparticles with Fe{sub 3}O{sub 4} cores were functionalized with antibiotics (rifampicin or chlortetracycline) as potential candidates for in vivo biomedical applications, such as magnetically controlled drug delivery. The synthesis consisted in coprecipitation of iron oxide in basic, as well as in acid medium, followed by the dispersion of the resulted magnetite nanoparticles in aqueous solution containing the antibiotic. The chosen method to prepare the magnetite-core/drug-shell systems avoided intermediate organic coating of the magnetic nanoparticles. Comparative analysis of the rheological features of the aqueous magnetic fluid samples was performed. The structural features of the coated magnetic particles were investigated by X-Ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and Vibrating Sample Magnetometry (VSM). Good crystallinity and adequate stability in time were evidenced. Drug delivery curves were spectrophotometrically provided.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2011

Structure and magnetic properties of three-dimensional (La,Sr)MnO{sub 3} nanofilms on ZnO nanorod arrays

Three-dimensional (3D) cubic perovskite (La,Sr)MnO{sub 3} (LSMO) nanofilms have been deposited on ZnO nanorod arrays with controlled dimensionality and crystallinity by radio frequency (rf) magnetron sputtering and post thermal annealing. Compared to the two-dimensional (2D) LSMO nanofilm on flat Si, the structure and magnetic properties of 3D LSMO nanofilms on ZnO nanorod arrays have a strong anisotropic morphology and thickness dependence. Ferromagnetic property has been observed in both 2D and 3D LSMO nanofilms while a ferromagnetic-superparamagnetic transition was revaled in 3D LSMO nanofilms on ZnO nanorod array with decreasing nanofilm thickness, due to a large surface dispersion effect. The LSMO/ZnO nanofilm/nanorod structures could open up new avenues for intriguing magnetic properties studies and applications of nanoscale perovskites.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2011

Magnetostructural phase transition in electroless-plated Ni nanoarrays

Ni nanoarrays were synthesized by electroless-plating and shaped by an anodic aluminum oxide template. The as-plated arrays exhibited superparamagnetic (SM) ordering resulting from nanocrystalline microstructure. Ferromagnetic (FM) ordering was found to be restored as the arrays' crystallinity was enhanced upon post-annealing. The microstructure (crystallinity) and the FM ordering are strongly coupled, revealing a magneto-structural correlation for the arrays. The magnetostructural properties of the arrays can be controlled by post-annealing, where the magnetization is proportional to the annealing temperature. The electroless-plated arrays synthesized in this work display magnetic anisotropy not found in electroplated ones. This is likely attributed to the nature of the clusterlike microstructure, whose cluster-boundaries may confine the FM rotation within the cluster. The spin-polarization was probed by x-ray magnetic circular dichroism while the arrays underwent the SM{yields}FM phase transition. The sum-rules results reveal that the total magnetization of the arrays is dominated by spin moment (m{sub spin}). The change in m{sub spin} is responsible for the SM{yields}FM phase transition upon annealing, as well as for the loss of magnetization upon temperature increase that we observed macroscopically.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2012

Efficiently recyclable magnetic core-shell photocatalyst for photocatalytic oxidation of chlorophenol in water

Multifunctional Fe{sub 3}O{sub 4}-TiO{sub 2} core-shell submicron particles were fabricated by a simple surface modification process that induces the magnetic submicron particles to be coated with a TiO{sub 2} shell. As characterized by field emission scanning electron microscopy, (FESEM), the as-synthesized Fe{sub 3}O{sub 4}-TiO{sub 2} particles exhibit a narrow size distribution with a typical size of 248 {+-} 19 nm and 8 nm in shell thickness. Magnetic measurement indicates that the as-synthesized Fe{sub 3}O{sub 4}-TiO{sub 2} core-shell particles are superparamagnetic at room temperature. Photocatalytic experiment is demonstrated by utilizing the oxidation reaction of 2,4,6-trichlorophenol (2,4,6-TCP) with the photofunctional magnetic nanoparticles.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Inter particle interaction in Ni{sub 0.5}Zn{sub 0.5}Fe{sub 2}O{sub 4} prepared by self combustion method

Ni{sub 0.5}Zn{sub 0.5}Fe{sub 2}O{sub 4} has been prepared by self combustion method and studied using X-ray diffraction, Moessbauer spectroscopy and DC magnetization techniques. X-ray diffractogram shows highly crystalline nano sized sample with no impurity phases. The room temperature Moessbauer and magnetization measurements show the co-existence of superparamagnetic and ferrimagnetic particles in the sample. The presence of inter particle interaction is confirmed from the {delta}M(H) curve at 20K. The dependence of magnetic moment below blocking temperature in the field cooling curve indicates that the inter particle interaction is weak in the as prepared sample.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Magnetically active vacancy related defects in irradiated GaN layers

We present the studies of magnetic properties of 2 MeV {sup 4}He{sup +}-irraadiated GaN grown by metal-organic chemical-vapor deposition. Particle irradiation allowed controllable introduction of Ga-vacancy in the samples. The magnetic moments with concentrations changing between 4.3 and 8.3 Multiplication-Sign 10{sup 17}cm{sup -3} showing superparamagnetic blocking at room temperature are observed. The appearance of clear hysteresis curve at T=5K with coercive field of about H{sub C} Almost-Equal-To 270 Oe suggests that the formation of more complex Ga vacancy related defects is promoted with increasing Ga vacancy content. The small concentration of the observed magnetically active defects with respect to the total Ga-vacancy concentration suggests that the presence of the oxygen/hydrogen-related vacancy complexes is the source of the observed magnetic moments.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Processing optimization and sintering time dependent magnetic and optical behaviors of Aurivillius Bi{sub 5}Ti{sub 3}FeO{sub 15} ceramics

Aurivillius Bi{sub 5}Ti{sub 3}FeO{sub 15} (BTF) ceramics were synthesized using the conventional solid state reaction method by optimizing excess of Bi{sub 2}O{sub 3} and sintering time. Their structures, magnetic, and optical properties were investigated in detail. The optimum process to sinter pure Aurivillius BTF ceramics was confirmed to be 3 wt. % excess Bi{sub 2}O{sub 3} to compensate the Bi volatilization at 1050 Degree-Sign C for 240 min (BTF-240M). The microstructure and crystalline structure of the BTF ceramics had little dependence on the sintering time from the x-ray diffraction (XRD) and scanning electron microscopic data. Nevertheless, the magnetic and optical properties were closely related with the sintering time. The overall magnetic behavior of these BTF ceramics was superparamagnetic (SPM), whereas there were unambiguous clues for the existence of antiferromagnetic (AFM) interactions. However, whether the SPM behavior was intrinsic or arised from a tiny amount of spinel Fe{sub 3}O{sub 4} impurity phase cannot be thoroughly ruled out in the XRD detection limit in the present stage. The AFM interactions were weakened upon extending the sintering time. The effective magnetic moment ({mu}{sub eff}), however, demonstrated different dependency on the sintering time. It increased with the sintering time from 80 min to 240 min, and then dropped with further extending the sintering time. Compared with other BTF ceramics, the BTF-240M ceramic showed the highest values of the refractive index n and real part {epsilon}{sub 1}, as well as the lowest ones of the extinction coefficient k and imagine part {epsilon}{sub 2} in whole photon energy range. Finally, a direct inter-band transition was confirmed for these BTF ceramics and optical energy band gaps were determined to be about 3.08, 3.18, and 3.39 eV for 80 min, 150 min, and 240 min sintered BTF ceramics, respectively, yet abnormal optical behavior was observed in BTF-360M ceramic.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Stimuli responsive magnetic nanogels for biomedical application

We report the synthesis and characterization of magnetic nanogels based on magnetite nanoparticles sterically stabilized by double layer oleic acid in water carrier and chemically cross linked poly (N-isopropylacril amide) (pNIPA) and poly (acrylic acid) (pAAc). In this structure the magnetite nanoparticles are attached to the flexible network chain by adhesive forces, resulting in a direct coupling between magnetic and elastic properties. Stable water suspensions of dual responsive magnetic nanogels based on temperature-responsive N-isopropyl acryl amide, pH responsive acrylic acid were obtained. The FTIR spectra of p(NIPA-AAc) ferrogel samples, showed the absorption region of the specific chemical groups associated with pNIPA, pAAc and the Fe{sub 3}O{sub 4} magnetic nanoparticles. The morphology and the structure of the as prepared materials were confirmed by transmission electron microscopy (TEM) and the size distribution was determined by dynamic light scattering (DLS). The magnetic microgels have high magnetization and superparamagnetic behaviour being suitable materials for biomedical application.

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

The Cr-substitution concentration dependence of the structural, electric and magnetic behaviors for Aurivillius Bi{sub 5}Ti{sub 3}FeO{sub 15} multiferroic ceramics

Aurivillius Bi{sub 5}Ti{sub 3}FeO{sub 15} (BTFO) multiferroic ceramics with different Cr-doped concentrations have been synthesized by the conventional solid state reaction method. The influences of Cr-doping concentrations on the structural, magnetic, dielectric, and ferroelectric properties of BTFO ceramics are investigated in detail. All these sintered Cr-substituted BTFO ceramics are determined to be layered perovskite Aurivillius structure by X-ray diffraction, as well as the lattice parameters a, b, and c are in good accordance with Vegard's law along with the Cr-doping concentration. The lattice distortion a/b for Aurivillius family decreases with increasing Cr-doping concentration. Moreover, Cr-doping can promote greatly the grain growth of BTFO samples confirmed from field emission scanning electron microscopy characterization. However, no obvious signs of the improvement in ferroelectric properties are found in Cr-doped BTFO ceramics, and abnormal ferroelectric polarization versus electric field (P-E) loops are observed as Cr-doping content is beyond 0.1. Similar ε (tanδ) versus frequency plots to those of the BTFO sample are exhibited when Cr-doping concentration is less than 0.1. Nevertheless, obvious dielectric dispersion phenomena are shown as the Cr-doping concentration is beyond 0.1, and this dispersion behavior becomes strong with further increasing Cr-doping concentration, which are clearly indicated by the appearance of dielectric loss relaxation peaks in the measurement frequency from 10{sup 2} Hz to 10{sup 6} Hz. In addition, the corresponding frequency to relaxation peak shifts towards high frequencies with the Cr-doping concentration. Finally, the same magnetic orderings for all these Cr-doped BTFO ceramics as those of the BTFO one, i.e., superparamagnetic state dominated with antiferromagnetic interaction, are unambiguously found, signifying that the predicted Fe{sup 3+}-O-Cr{sup 3+} 180° ferromagnetic superexchange interaction based on the Goodenough-Kanamori (G-K) rule might not be achieved in BTFO ceramics through Cr substitution by the conventional solid state reaction.

36 MATERIALS SCIENCE↗