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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

PVA and PEG functionalised LSMO nanoparticles for magnetic fluid hyperthermia application

La{sub 0.7}Sr{sub 0.3}MnO{sub 3} magnetic nanoparticles are synthesized by a solution combustion method and functionalised with polyvinyl alcohol and polyethylene glycol. The induction heating characteristics of coated magnetic nanoparticles (42 °C) were observed at a reasonably low concentration (5 mg/mL). Remarkably, coated magnetic nanoparticles exhibited a promisingly high specific absorption rate with varying magnetic field and constant frequency. The surface analysis is carried out by X-ray photoelectron spectroscopy. A reduction in the agglomeration of the particles was observed when the magnetic nanoparticles were functionalised with polyvinyl alcohol or polyethylene glycol and can be confirmed by transmission electron microscopy and dynamic light scattering studies. Vibrating sample magnetometer measurements indicate superparamagnetic behaviour at room temperature before and after coating. Colloidal stability revealed a considerably higher zeta potential value for coated system. In vitro cytotoxicity test of the magnetic nanoparticles indicates that coated nanoparticles have no significant effect on cell viability within the tested concentrations (1–5 mg mL{sup -1}) as compared to uncoated La{sub 0.7}Sr{sub 0.3}MnO{sub 3}. All these findings explore the potentiality of La{sub 0.7}Sr{sub 0.3}MnO{sub 3} nanoparticles for magnetic fluid hyperthermia. - Highlights: • Surface functionalization of LSMO nanoparticles — first time with PVA • Surface functionalization of LSMO nanoparticles — first time with PEG • BSA protein — first time used as dispersion medium for stability of LSMO nanoparticles • The heating ability observed at low concentration • Improved efficiency of magnetic fluid hyperthermia treatment with surfactants.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2010

Magnetization studies on {epsilon}-Fe{sub 2.4}Co{sub 0.6}N nanoparticles

{epsilon}-Fe{sub 2.4}Co{sub 0.6}N nanoparticles are prepared by nitridation of ultrafine iron-cobalt oxide in NH{sub 3} gas atmosphere at 873 K for 3 h. Their magnetic properties are studied using ac and dc magnetization techniques. Two peaks at 69 and 151 K are found in ac susceptibility study. The former peak is assigned to superparamagnetic blocking temperature (T{sub B} {approx} 69 K), whereas the origin of the latter one could not be ascertained since it is observed only from imaginary part of ac susceptibility study. The positions of peaks are found to be dependent on the applied fields and frequencies. Also, dc magnetization studies corroborate T{sub B}. Anisotropy constant (K{sub a}) is found to be 2.3 x 10{sup 5} erg/cm{sup 3}. The peaks disappear at high-applied field due to the overcome of applied filed over anisotropic energy. Ferromagnetic domains rotate incoherently. At low temperature, Bloch law cannot be applied, but Curie law can be applied above T{sub B}. Interestingly, spin relaxation is faster at 10 K as compared to that at 70 K indicating the presence of frustration of spins at lower temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2010

Structural and magnetic properties of a mechanochemically activated Ti-Fe{sub 2}O{sub 3} solid mixture

The mechanochemical effects on the reactivity and properties of a titanium/hematite powder mixture with molar ratio of 1/2 are investigated. Crystalline-phase structure, composition, hyperfine and magnetic behaviors were analyzed as a function of activation time by means of X-ray diffraction, scanning electron microscopy, Moessbauer spectroscopy and vibrating sample magnetometry. The results showed that at relatively short activation times metallic Ti reduces part of the ferric ions, yielding a complex product formed mainly by a mix of two solid solutions Fe{sub 3-x}Ti{sub x}O{sub 4} (titanomagnetites), both with very different x values (0 < x < 1). Also metallic iron and superparamagnetic hematite particles were detected by Moessbauer spectroscopy. As the mechanical treatment extends the composition of the reactive mixture changes, prevailing in the end the solid solution with higher x value. In contrast, when these activated samples are thermally treated the fraction of the solid solution which is richer in Ti diminishes. This fact produces a significant variation of the saturation magnetization of the obtained material.

36 MATERIALS SCIENCE↗
DOE OSTI2011

Magnetic phase composition of strontium titanate implanted with iron ions

Highlights: Black-Right-Pointing-Pointer The origin of RT-ferromagnetism in iron implanted strontium titanate. Black-Right-Pointing-Pointer Metallic iron nanoclusters form during implantation and define magnetic behaviour. Black-Right-Pointing-Pointer Paramagnetic at room temperature iron-substituted strontium titanate identified. -- Abstract: Thin magnetic films were synthesized by means of implantation of iron ions into single-crystalline (1 0 0) substrates of strontium titanate. Depth-selective conversion electron Moessbauer spectroscopy (DCEMS) indicates that origin of the samples magnetism is {alpha}-Fe nanoparticles. Iron-substituted strontium titanate was also identified but with paramagnetic behaviour at room temperature. Surface magneto-optical Kerr effect (SMOKE) confirms that the films reveal superparamagnetism (the low-fluence sample) or ferromagnetism (the high-fluence sample), and demonstrate absence of magnetic in-plane anisotropy. These findings highlight iron implanted strontium titanate as a promising candidate for composite multiferroic material and also for gas sensing applications.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Electromagnetic and microwave-absorbing properties of magnetite decorated multiwalled carbon nanotubes prepared with poly(N-vinyl-2-pyrrolidone)

Graphical abstract: The Fe{sub 3}O{sub 4}/MWNTs hybrids prepared with PVP achieve a maximum reflection loss is -35.8 dB at 8.56 GHz, and the bandwidth below -10 dB is more than 2.32 GHz. More importantly, a new reflection loss peak occurs at the frequency of 14.6 GHz, which indicates that the Fe{sub 3}O{sub 4}/MWNTs hybrids have better absorption properties in the high-frequency range. Highlight: Black-Right-Pointing-Pointer The Fe{sub 3}O{sub 4} decorated MWNTs hybrids were prepared using PVP as dispersant. Black-Right-Pointing-Pointer Many more Fe{sub 3}O{sub 4} particles were attached homogeneously on the surface of MWNTs. Black-Right-Pointing-Pointer The Fe{sub 3}O{sub 4}/MWNTs hybrids achieve a maximum reflection loss of -35.8 dB at 8.56 GHz. Black-Right-Pointing-Pointer A new reflection loss peak occurs at the high-frequency of 14.6 GHz. -- Abstract: The magnetite (Fe{sub 3}O{sub 4}) decorated multiwalled carbon nanotubes (MWNTs) hybrids were prepared by an in situ chemical precipitation method using poly(N-vinyl-2-pyrrolidone) (PVP) as dispersant. The structure and morphology of hybrids are characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and transmission electron-microscopy (TEM). The TEM investigation shows that the Fe{sub 3}O{sub 4}/MWNTs hybrids exhibit less entangled structure and many more Fe{sub 3}O{sub 4} particles are attached homogeneously on the surface of MWNTs, which indicated that PVP can indeed help MWNTs to disperse in isolated form. The electromagnetic and absorbing properties were investigated in a frequency of 2-18 GHz. The results show that the Fe{sub 3}O{sub 4}/MWNTs hybrids exhibit a superparamagnetic behavior and possess a saturation magnetization of 22.9 emu/g. The maximum reflection loss is -35.8 dB at 8.56 GHz, and the bandwidth below -10 dB is more than 2.32 GHz. More importantly, a new reflection loss peak occurs at the frequency of 14.6 GHz, which indicates that the Fe{sub 3}O{sub 4}/MWNTs hybrids have better absorption properties in the high-frequency.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Fe{sub 3}O{sub 4} and CdS based bifunctional core–shell nanostructure

Highlights: ► First report on a room temperature aqueous process for growth of a hybrid core shell nanostructure containing a magnetic core and a semiconducting shell. ► Formation of distinct core shell nanostructure revealed by high resolution transmission electron microscopy. ► A bifunctional nature combining magnetic as well as photoresponce for the as synthesised core shell nanostructures demonstrated. ► A tendency towards self organisation of the core–shell nanostructure. ► Possible applications including purification and isolation of biological materials, drug delivery system, bio-labels, spintronics, etc. -- Abstract: A room temperature solution process for synthesis of Fe{sub 3}O{sub 4} nanoparticles and their hybrid core shell nanostructures using CdS as the shell material has been described. The as grown particles have been characterised using XRD, Rietveld refinement, high resolution transmission electron microscopy, atomic force microscopy, superconducting quantum interference device, optical absorbance and photoluminescence spectroscopy. A superparamagnetic response revealed from the magnetisation measurements of the as synthesised magnetite nanoparticles was retained even after the growth of the CdS shell. From luminescence and high resolution atomic force microscopy measurements, it is shown that the core–shell structures advantageously combine magnetic as well as fluorescence response with a tendency towards self-organization.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Preparation of magnetic photocatalyst nanoparticles—TiO{sub 2}/SiO{sub 2}/Mn–Zn ferrite—and its photocatalytic activity influenced by silica interlayer

Highlights: ► TiO{sub 2}/SiO{sub 2}/Mn–Zn ferrite acts as magnetic photocatalyst nanoparticle. ► SiO{sub 2} interlayer is used to prevent electron migration between photocatalyst and magnetic core. ► TiO{sub 2}/Mn–Zn ferrite without SiO{sub 2} interlayer shows poor magnetic and photocatalytic property. -- Abstract: A magnetic photocatalyst, TiO{sub 2}/SiO{sub 2}/Mn–Zn ferrite, was prepared by stepwise synthesis involving the co-precipitation of Mn–Zn ferrite as a magnetic core, followed by a coating of silica as the interlayer, and titania as the top layer. The particle size and distribution of magnetic nanoparticles were found to depend on the addition rate of reagent and dispersing rate of reaction. The X-ray diffractometer and transmission electron microscope were used to examine the crystal structures and the morphologies of the prepared composites. Vibrating sample magnetometer was also used to reveal their superparamagnetic property. The UV–Vis spectrophotometer was employed to monitor the decomposition of methylene blue in the photocatalytic efficient study. It was found that at least a minimum thickness of the silica interlayer around 20 nm was necessary for the inhibition of electron transference initiated by TiO{sub 2} and Mn–Zn ferrite.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Co{sub 1−x}Zn{sub x}Fe{sub 2}O{sub 4} (0 ≤ x ≤ 1) nanocrystalline solid solution prepared by the polyol method: Characterization and magnetic properties

Highlights: ► Co–Zn ferrite nanoparticles were produced by soft chemistry. ► Cation distribution deviation from the thermodynamically stable one was evidenced. ► The magnetic characteristics were affected and differ from those of bulks. -- Abstract: Highly crystalline stoichiometric Co{sub 1−x}Zn{sub x}Fe{sub 2}O{sub 4} (0 ≤ x ≤ 1) nanoparticles were successfully synthesized by the polyol process. X-ray diffraction (XRD), X-ray fluorescence spectroscopy (XRF), transmission electron microscopy (TEM), infrared spectroscopy (IR), zero-field {sup 57}Fe Mössbauer spectrometry and magnetic measurements using a SQUID magnetometer were employed to investigate the effect of the substitution of Zn{sup 2+} ions for Co{sup 2+} ones on the structure, and the magnetic properties of the cobalt ferrite, CoFe{sub 2}O{sub 4}. The unit cell parameter almost increases linearly with increasing Zn concentration, x, following Vegard's law. The red and blue shifts observed for the metal-oxygen ν{sub 1} and ν{sub 2}IR vibration bands, respectively, were consistent with the preferential entrance of Zn{sup 2+} ions in tetrahedral sites. Besides, detailed magnetic investigation in correlation with the cation distribution has been reported. All the particles exhibit superparamagnetic behaviour at room temperature. In addition, the magnetic characteristics (blocking temperature, saturation magnetization, coercivity, Curie temperature) clearly depend on the chemical composition and cation distribution. Both the blocking temperature and Curie temperature decrease drastically with Zn composition, x, increase. Further, the saturation magnetization follows an almost bulk-like behaviour with values notably larger than that of the bulk, mainly attributed to cation distribution deviation.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Solvothermal in situ synthesis of Fe{sub 3}O{sub 4}-multi-walled carbon nanotubes with enhanced heterogeneous Fenton-like activity

Graphical abstract: After purification, the multi-wall carbon nanotubes (MWCNTs) act as seeds for Fe{sub 3}O{sub 4} nanoparticles heterogeneous nucleation. The Fe{sub 3}O{sub 4} nanoparticles with diameter range of 4.2–10.0 nm synthesized in situ on the MWCNTs under solvothermal condition. The formed nano Fe{sub 3}O{sub 4}-MWCNTs decolorized the Acid Orange II effectively via Fenton-like reaction. Highlights: ► The amount of water tunes size and size distribution of the Fe{sub 3}O{sub 4} nanoparticles (FNs). ► FNs are homogeneously coated on the multi-walled carbon nanotubes (MWCNTs). ► FNs have diameters in the range of 4.2–10.0 nm, average grain size of 7.4 nm. ► Fe{sub 3}O{sub 4}-MWCNTs are used as a Fenton-like catalyst to decompose Acid Orange II. ► Fe{sub 3}O{sub 4}-MWCNTs displayed a higher activity than nanometer-size Fe{sub 3}O{sub 4}. -- Abstract: Fe{sub 3}O{sub 4}-multi-walled carbon nanotubes (Fe{sub 3}O{sub 4}-MWCNTs) hybrid materials were synthesized by a solvothermal process using acid treated MWCNTs and iron acetylacetonate in a mixed solution of ethylene glycol and ultrapure water. The materials were characterized using X-ray powder diffraction, scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, and vibrating sample magnetometry. The results showed that a small amount of water in the synthesis system played a role in controlling crystal phase formation, size of Fe{sub 3}O{sub 4}, and the homogeneous distribution of the Fe{sub 3}O{sub 4} nanoparticles deposited on the MWCNTs. The Fe{sub 3}O{sub 4} nanoparticles had diameters in the range of 4.2–10.0 nm. They displayed good superparamagnetism at room temperature and their magnetization was influenced by the reaction conditions. They were used as a Fenton-like catalyst to decompose Acid Orange II and displayed a higher activity than nanometer-size Fe{sub 3}O{sub 4}.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Synthesis and characterization of NiFe{sub 2}O{sub 4}–Pd magnetically recyclable catalyst for hydrogenation reaction

Graphical abstract: Display Omitted Highlights: ► Novel superparamagnetic NiFe{sub 2}O{sub 4}–Pd magnetically recyclable catalyst was fabricated through co-precipitation. ► It could be reused several times without significant loss in catalytic activity for hydrogenation reaction. ► No further modification of the NiFe{sub 2}O{sub 4}–Pd magnetically recyclable catalyst is necessary for utilization as catalyst. -- Abstract: Herein we report the fabrication and characterization magnetically recyclable catalysts of NiFe{sub 2}O{sub 4}–Pd nanocomposite as highly effective catalysts for reduction reactions in liquid phase. The reduction Pd{sup 2+} was accomplished with polyethylene glycol 400 (PEG-400) instead of sodium borohydride (NaBH{sub 4}) and NiFe{sub 2}O{sub 4} nanoparticles was prepared by sonochemically using FeCI{sub 3}·6H{sub 2}O and NiCl{sub 2}. The chemical characterization of the product was done with X-ray diffractometry, Infrared spectroscopy, transmission electron microscopy, UV–Vis spectroscopy, thermal gravimetry and inductively coupled plasma. Thus formed NiFe{sub 2}O{sub 4}–Pd MRCs showed a very high activity in reduction reactions of 4-nitro aniline and 1,3-dinitrobenzene in liquid phase. It was found out that the catalytic activity of NiFe{sub 2}O{sub 4}–Pd MRCs on the reduction of 4-nitro aniline and 1,3-dinitrobenzene in liquid phase are between 99–93% and 98–93%, respectively. Magnetic character of this system allowed recovery and multiple use without significant loss of its catalytic activity. It is found that NiFe{sub 2}O{sub 4}–Pd MRCs showed very efficient catalytic activity and multiple usability.

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

Simple solvothermal synthesis of hydrophobic magnetic monodispersed Fe{sub 3}O{sub 4} nanoparticles

Graphical abstract: A facile method to produce monodispersed magnetite nanoparticles is based on the solvothermal reaction of iron acetylacetonate (Fe(acac)3) decomposition. The sizes ranged from 7 to 12 nm, which could be controlled by adjusting the volume ratio of oleylamine to n-hexane. Display Omitted Highlights: ► The solvethermal reaction of Fe(acac){sub 3} decomposition was carried out at mild temperature in the presence of oleylamine and n-hexane. ► The size of nanocrystals is controlled by adjusting the volume ratio of oleylamine to n-hexane. ► The low-boiling-point solvent n-hexane offered autogenous pressure parameter after gasified in the reaction temperature. ► The as prepared hydrophobic monodisperse Fe{sub 3}O{sub 4} NPs can be used to prepare the magnetic micelles for future biomedical applications. -- Abstract: A new solvothermal method is proposed for the preparation of Fe{sub 3}O{sub 4} nanoparticles (NPs) from iron acetylacetonate in the presence of oleylamine and n-hexane. The products are characterized by X-ray powder diffraction, infrared (IR) spectroscopy, transmission electron microscopy, thermogravimetry/differential thermogravimetry (TG/DTG) analysis, and vibrating sample magnetometery. The new procedure yields superparamagnetic monodispersed Fe{sub 3}O{sub 4} particles with sizes ranging from 7 nm to 12 nm. The nanocrystal sizes are controlled by adjusting the volume ratio of oleylamine to n-hexane. IR and TG/DTG analyses indicate that the oleylamine molecules, as stabilizers, are adsorbed on the surface of Fe{sub 3}O{sub 4} NPs as bilayer adsorption models. The surface adsorption quantities of oleylamine on 7.5 and 10.4 nm-diameter Fe{sub 3}O{sub 4} NPs are 18% and 11%, respectively. The hydrophobic surface of the obtained nanocrystals is passivated by adsorbed organic solvent molecules. These molecules provide stability against agglomeration, enable solubility in nonpolar solvents, and allow the formation of magnetic polymer micelles.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Facile synthesis of QD-anchored composite particles with magnetite cluster cores ({sup n}Fe{sub 3}O{sub 4}@SiO{sub 2}@QDs)

Highlights: ► Triple layered Fe{sub 3}O{sub 4}/SiO{sub 2}/QDs were designed as fluorescent magnetic nanocomposites. ► Magnetite cluster-embedded silica exhibited strong and controllable magnetism. ► Effective conjugation between QDs and magnetic silica occurred at pH3. - Abstract: Magnetism-controlled fluorescent composite particles ({sup n}Fe{sub 3}O{sub 4}@SiO{sub 2}@QDs) were prepared as QD-anchored silica nanoparticles with magnetite cluster cores. First, citrate-capped magnetites (C-Fe{sub 3}O{sub 4}) were prepared by the co-precipitation method and subsequently complexed with 3-aminopropyl-trimethoxysilane (APTMS) at room temperature, consequently leading to the formation of magnetite clusters (A-{sup n}Fe{sub 3}O{sub 4}) with alkoxy terminated interfaces. The sol–gel reaction between A-{sup n}Fe{sub 3}O{sub 4} and tetraethoxysilane (TEOS) produced the core-shell {sup n}Fe{sub 3}O{sub 4}@SiO{sub 2}. The resulting core-shell particles exhibited superparamagnetic properties and controllable magnetism simply by adjusting the thickness of nonmagnetic silica layer. After then, amine-terminated {sup n}Fe{sub 3}O{sub 4}@SiO{sub 2} (NH{sub 2}–{sup n}Fe{sub 3}O{sub 4}@SiO{sub 2}) was conjugated with carboxy quantum dots (QDs) using an EDC coupling agent. The QD conjugation with NH{sub 2}–{sup n}Fe{sub 3}O{sub 4}@SiO{sub 2} of lower pH exhibited the higher photoluminescence (PL) intensity, and the resulting composite particles ({sup n}Fe{sub 3}O{sub 4}@SiO{sub 2}@QDs) can be a useful biomedical agent. This chemical strategy can be further applied to prepare the core-shell magnetic nanostructure with various oxide layers for specific applications.

36 MATERIALS SCIENCE↗
DOE OSTI2013

One-step room temperature synthesis of very small γ-Fe{sub 2}O{sub 3} nanoparticles

Graphical abstract: - Highlights: • One-step synthesis of 3 nm maghemite nanoparticles is reported. • Maghemite nanoparticles can be synthesized from a ferric solution. • γ-Fe{sub 2}O{sub 3} NPs can be obtained if the precursor has Fe(III) in tetrahedral interstices. • HR-TEM, Mössbauer, XAFS and magnetometry analysis proved the maghemite existence - Abstract: Very small maghemite nanoparticles (∼3 nm) are obtained through a one-step synthesis at room temperature. The fast neutralization reaction of a ferric solution in a basic medium produces an intermediate phase, presumably two-line ferrihydrite, which in oxidizing conditions is transformed to maghemite nanoparticles. The synthesis of maghemite, as final product of the reaction, was characterized by High-Resolution Transmission Electron Microscopy (HR-TEM), X-ray Absorption Fine Structure (XAFS), Mössbauer spectroscopy, and magnetometry. The XAFS technique allowed the analysis of the crystallographic variations into maghemite nanoparticles as a result of modification in its surface/volume ratio. Mössbauer spectroscopy at low temperature (4.2 K) confirms the presence of Fe(III) in tetrahedral and octahedral interstices, in the stoichiometry corresponding to maghemite. The specific magnetization, M vs H (3 K and 300 K, up to 7 T) and temperature dependence of the magnetization (50 Oe by ZFC mode, 2 K ≤ T ≤ 300 K) indicate that maghemite nanoparticles of 3 nm are in superparamagnetic state with a blocking temperature close to 36 K.

36 MATERIALS SCIENCE↗
DOE OSTI2013

A novel solvethermal method for the preparation of magnetic monodisperse Fe{sub 3}O{sub 4} nanoparticles II: High-surface-activity ferrihydrite used as precursor

Graphical abstract: The magnetic monodisperse Fe{sub 3}O{sub 4} nanoparticles (NPs) were prepared by novel solvethemal method at moderate temperature using high surface active ferrihydrit and iron powder as precursors in orgnic solvent. - Highlights: • Facile synthesis of organic ligands-coated monodisperse Fe{sub 3}O{sub 4} nanoparticles at low temperature. • Low-cost high surface active ferrihydrit and reductive iron powder were used as precursors. • N{sub 2}-free reaction environment. • Organic ligands act as reductive. - Abstract: Magnetic monodisperse Fe{sub 3}O{sub 4} nanoparticles (NPs) were prepared from ferrihydrite and iron powder by a novel solvethermal method at moderate temperatures in aqueous and organic solvent media. The effects of temperature and solvent medium on the phase and particle size of Fe{sub 3}O{sub 4} NPs were investigated. The products were characterized by X-ray powder diffraction, infrared spectroscopy, differential scanning calorimetry–thermogravimetric analysis, transmission electron microscopy, and vibrating sample magnetometry. At 120 °C in the organic medium, uniform organic-ligand-coated superparamagnetic Fe{sub 3}O{sub 4} NPs were produced; the particle size increased with the temperature, and the calculated mean particle size was 8.9 nm. At 180 °C in the aqueous medium, pure-phase Fe{sub 3}O{sub 4} was obtained. Thus, the organic solvent did not only serve as a solvent but also participated in the reaction. Fe{sub 3}O{sub 4} production in the aqueous and organic solvent media had different mechanisms.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Magnetic properties of nanocrystalline ε-Fe{sub 3}N and Co{sub 4}N phases synthesized by newer precursor route

Graphical abstract: Nanocrystalline ε-Fe{sub 3}N and Co{sub 4}N nitride phases are synthesized first time by newer chemical routes. The ε-Fe{sub 3}N phase crystallizes in hexagonal structure with unit cell parameters, a = 4.76 Å and c = 4.41 Å. The Co{sub 4}N phase crystallizes in face centred cubic (fcc) structure with unit cell parameters, a = 3.55 Å. The estimated crystallite size for ε-Fe{sub 3}N and Co{sub 4}N phases are 29 nm and 22 nm, respectively. The values of saturation magnetization for ε-Fe{sub 3}N and Co{sub 4}N phases are found to be 28.1 emu/g and 123.6 emu/g respectively. The reduction of magnetic moments in ultrafine materials compared to bulk materials has been explained by fine particle size and surface effects. We have synthesized the high moment ε-Fe{sub 3}N and Co{sub 4}N nitride with reduced coercivity which may find applications as soft magnetic materials. - Highlights: • Nanocrystalline ε-Fe{sub 3}N and Co{sub 4}N nitride phases are synthesized. • The ε-Fe{sub 3}N and Co{sub 4}N crystallizes in hexagonal and fcc structure respectively. • The observed magnetic parameters indicate soft magnetic properties. • The magnetic properties have been explained on the basis of fine particle magnetism. - Abstract: Nanocrystalline ε-Fe{sub 3}N and Co{sub 4}N nitride phases are synthesized first time by using tris(1,2-diaminoethane)iron(II) chloride and tris(1,2-diaminoethane)cobalt(III) chloride precursors, respectively. To prepare ε-Fe{sub 3}N and Co{sub 4}N nitride phases, the synthesized precursors were mixed with urea in 1:12 ratio and heat treated at various temperatures in the range of 450–900 °C under the ultrapure nitrogen gas atmosphere. The precursors are confirmed by FT-IR study. The ε-Fe{sub 3}N phase crystallizes in hexagonal structure with unit cell parameters, a = 4.76 Å and c = 4.41 Å. The Co{sub 4}N phase crystallizes in face centred cubic (fcc) structure with unit cell parameters, a = 3.55 Å. The estimated crystallite size for ε-Fe{sub 3}N and Co{sub 4}N phases are 29 nm and 22 nm, respectively. The scanning electron microscopy (SEM) studies confirm the nanocrystalline nature of the materials. The values of saturation magnetization for ε-Fe{sub 3}N and Co{sub 4}N phases are found to be 28.1 emu/g and 123.6 emu/g, respectively. The reduction of magnetic moments in ultrafine materials compared to bulk materials have been explained by spin pairing effect, lattice expansion, superparamagnetic behaviour and canted spin structures at the surface of the particles.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Synthesis of Fe/SiO{sub 2} and iron oxides/SiO{sub 2} nanocomposites by long-term ball milling

Graphical abstract: - Highlights: • Iron–iron oxides/silica composites are synthesized by long term dry ball-milling. • Bcc iron and α-quartz powders are used as precursors. • Surface effects enhance coercivity in iron/silica nanocomposites. • In spite of their small size, about 10 nm, iron particles are ferromagnetic. • Ferro and superparamagnetic particles are found in maghemite/silica composites. - Abstract: Iron oxide/SiO{sub 2} nanocomposites are synthesized by dry ball-milling a mixture of bcc Fe and α-quartz powders for prolonged times. A sequence of nanocomposites is obtained, with small magnetic particles dispersed in a non magnetic, amorphous matrix. The powders are characterized by X-ray diffraction and transmission electron microscopy. The magnetic hysteresis properties are investigated in the range 50–300 K. After 120 h milling, deformed, non-spherical, α-Fe nanocrystallites of about 10 nm in size and very few small (<10 nm) maghemite particles are found. At room temperature, iron particles are ferromagnetic and a large effective magnetic anisotropy is estimated, which is mainly attributed to surface effects. Between 160 and 200 h milling, maghemite nanoparticles are observed while after 220 h grinding, hematite phase appears; after 340 h milling, the sample consists of ferromagnetic hematite particles with a broad size distribution (5–50 nm) embedded in an amorphous matrix.

36 MATERIALS SCIENCE↗
DOE OSTI2014

A facile gel-combustion route for fine particle synthesis of spinel ferrichromite: X-ray and Mössbauer study on effect of Mg and Ni content

Highlights: • A novel and facile synthesis route. • Transformation of system from random to inverse spinel. • Appearance of superparamagnetism phase. - Abstract: A novel nitrate–citrate gel combustion route was used to prepare fine particle of a series Mg{sub 1−x}Ni{sub x}FeCrO{sub 4} (0.0 ≤ x ≤ 1.0) and its structural properties were investigated. The in situ oxidizing environment provided by the nitrate ions in the gel increases the rate of oxidation and lowers the decomposition temperature of component. All the samples after sintering were characterized at room temperature by X-ray diffraction (XRD) method and Mössbauer spectroscopy techniques. The X-ray and Mössbauer studies confirmed the single phase cubic spinel structure with all Fe ions in 3+ charge state. XRD and Mössbauer studies revealed that the samples of x = 0.0, and 0.2 are random spinel and show rather broad lines, while x = 0.4–1.0 are inverse spinel.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Hyperfine and magnetic properties of a Y{sub x}La{sub 1−x}FeO{sub 3} series (0 ≤ x ≤ 1)

Highlights: • Y{sub x}La{sub 1−x}FeO{sub 3} (0 ≤ x ≤ 1) was synthesized by mechanochemistry. • Two magnetic contributions were identified in the series. • A paramagnetic state is associated with a fraction of the smallest particles. • A ferromagnetic state is attributed to the larger particles. • Annealing of samples favored the formation of Y{sub 3}Fe{sub 5}O{sub 12} impurities. - Abstract: A series of orthoferrites Y{sub x}La{sub 1−x}FeO{sub 3} in the entire range of composition was synthesized at room temperature by mechanochemical activation of oxide mixtures. Phase composition, structure and microstructure of the obtained powder materials were characterized by X-ray diffraction and field-emission scanning electron microscopy. Hyperfine interactions and magnetic properties were determined by Mössbauer spectroscopy, SQUID and vibrating sample magnetometry. Two magnetic contributions could be identified in the series of materials: a paramagnetic state, associated with a fraction of the smallest particles and a ferromagnetic state, attributed to the larger particles. The results showed that the relative proportion of both contributions is very dependent on x, the Y content of samples. From M vs T measurements, it was possible to estimate the blocking temperature distribution for the end members of the series. Annealing of samples produced the elimination of the superparamagnetic behavior and the formation of Y{sub 3}Fe{sub 5}O{sub 12} impurities.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗