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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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

One-pot synthesis of stable colloidal solutions of MFe{sub 2}O{sub 4} nanoparticles using oleylamine as solvent and stabilizer

Highlights: ► One-pot synthesis of ferrite magnetic nanoparticles (<10 nm) in non-polar media. ► Nanoparticles present high monocrystal quality and monodispersion. ► Superparamagnetic behavior at room temperature. ► Nanoparticles transfer to polar media via ligand exchange. - Abstract: An easy, efficient, reproducible and scalable one-pot synthetic methodology to obtain magnetic spinel ferrite nanoparticles has been developed. This approach is based on one-pot thermal decomposition of Fe(acac){sub 3} and M(acac){sub 2} (M = Co, Mn, Cu and Zn) in oleylamine, which also acts as a capping ligand, by producing stable colloidal dispersions of nanoparticles in non-polar solvents. The properties of the nanoparticles have been studied via different techniques, such as transmission electron microscopy, which shows that nanoparticles are monocrystallines and a narrow dispersion in size; magnetic analyses have demonstrated that the resulting ferrite nanoparticles show high saturation values and superparamagnetic behavior at room temperature; X-ray diffraction has also been performed, and it confirms that the synthesized nanoparticles have a spinel structure. Complementarily, ligand exchange has been also carried out in order to produce dispersions of the synthesized nanoparticles in polar media.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Facile fabrication and characterization of amino-functionalized Fe{sub 3}O{sub 4} cluster@SiO{sub 2} core/shell nanocomposite spheres

Highlights: ► A method developed for the preparation of Fe{sub 3}O{sub 4} clusters@SiO{sub 2} nanocomposites. ► This method permits production of core/shell nanomaterials with high yields. ► Resultant superparamagnetic particles are monodisperse with high magnetizations. - Abstract: We developed a modified straightforward method for the fabrication of uniformly sized silica-coated magnetite clusters core/shell type nanocomposite particles. Proposed simple one-step processing method permits quick production of materials in high yield. The structural, surface, and magnetic characteristics of the nanocomposite particles were investigated by transmission electron microscopy (TEM), scanning electron microscope (SEM), powder X-ray diffraction (XRD), vibrating sample magnetometer (VSM), and Fourier-transform infrared (FTIR). The sphere-shaped particles almost have the average diameter of 120 nm, with a magnetic cluster core of 80 ± 15 nm, and a silica shell of 25 ± 10 nm thickness. The particles are superparamagnetic and present strong magnetization (18 emu/g) due to the fact that they possess core of the magnetic clusters. Subsequently, the silica surface of core/shell particles was amino-functionalized via N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (EDS). Findings of the present work highlight the potential for using amino-functionalized magnetic silica core/shell nanocomposite particles in biological applications since they possess useful magnetic properties and proper structure.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Nanocrystalline spinel ferrite (MFe{sub 2}O{sub 4}, M = Ni, Co, Mn, Mg, Zn) powders prepared by a simple aloe vera plant-extracted solution hydrothermal route

Graphical abstract: This figure shows the specific magnetization curves of the as-prepared MFe{sub 2}O{sub 4} (M = Ni, Co, Mn, Mg, Zn) powders obtained from room temperature VSM measurement. These curves are typical for a soft magnetic material and indicate hysteresis ferromagnetism in the field ranges of ±500 Oe, ±1000 Oe, and ±2000 Oe for the CoFe{sub 2}O{sub 4}, MgFe{sub 2}O{sub 4} and MnFe{sub 2}O{sub 4} respectively, whereas the samples of NiFe{sub 2}O{sub 4} and ZnFe{sub 2}O{sub 4} show a superparamagnetic behavior. Highlights: ► Nanocrystalline MFe{sub 2}O{sub 4} powders were synthesized by a novel hydrothermal method. ► Metal acetylacetonates and aloe vera plant-extracted solution are used. ► This biosynthetic route is very simple and provides high-yield oxide nanomaterials. ► XRD and TEM results indicate that the prepared samples have only spinel structure. ► The maximum M{sub s} of 68.9 emu/g at 10 kOe were observed for the samples of MnFe{sub 2}O{sub 4}. - Abstract: Nanocrystalline spinel ferrite MFe{sub 2}O{sub 4} (M = Ni, Co, Mn, Mg, Zn) powders were synthesized by a novel hydrothermal method using Fe(acac){sub 3}, M(acac){sub 3} (M = Ni, Co, Mn, Mg, Zn) and aloe vera plant extracted solution. The X-ray diffraction and selected-area electron diffraction results indicate that the synthesized nanocrystalline have only spinel structure without the presence of other phase impurities. The crystal structure and morphology of the spinel ferrite powders, as revealed by TEM, show that the NiFe{sub 2}O{sub 4} and CoFe{sub 2}O{sub 4} samples contain nanoparticles, whereas the MnFe{sub 2}O{sub 4} and MgFe{sub 2}O{sub 4} samples consist of many nanoplatelets and nanoparticles. Interestingly, the ZnFe{sub 2}O{sub 4} sample contains plate-like structure of networked nanocrystalline particles. Room temperature magnetization results show a ferromagnetic behavior of the CoFe{sub 2}O{sub 4}, MnFe{sub 2}O{sub 4} and MgFe{sub 2}O{sub 4} samples, whereas the samples of NiFe{sub 2}O{sub 4} and ZnFe{sub 2}O{sub 4} exhibit a superparamagnetic behavior.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Novel method of room temperature ionic liquid assisted Fe{sub 3}O{sub 4} nanocubes and nanoflakes synthesis

Graphical abstract: - Highlights: • First time [Bmim][TfO] IL is used for the Fe{sub 3}O{sub 4} nanoparticle synthesis. • Novel method tunes Fe{sub 3}O{sub 4} nanocubes and nanoflakes forms influenced by the base and IL. • Fe{sub 3}O{sub 4} oxidized topotactically into γ-Fe{sub 2}O{sub 3} nanoparticles by annealing and base. • Uniform morphology with average size of 33 nm negligible superstructure are formed. • Ms values are characterized by thin layer of γ-Fe{sub 2}O{sub 3} on the nanoparticle surface. - Abstract: For the first time, the nanomagnetite superparamagnetic particles are successfully synthesized by precipitation method using 1-n-butyl-3-methylimidazolium trifluoromethane sulfonate [Bmim][TfO] ionic liquid medium/surfactant. The obtained Fe{sub 3}O{sub 4} particles are nanocubes and nanoflakes and this formation is influenced by the base concentration and anisotropic circumstances produced by the ionic liquid and their size varies from 20 nm to 150 × 300 nm (width × length). The synthesized magnetite nanoparticles are characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), Raman spectroscopy, Field emission scanning electron microscopy (FE-SEM), Transmission electron microscopy (TEM) and Vibrating sample magnetometer (VSM) studies. The results show that the core of the Fe{sub 3}O{sub 4} nanoparticles is surrounded by a thin layer of γ-Fe{sub 2}O{sub 3} by topotactical partial oxidation, which is remarkably proceed with the subsequent calcination. The magnetite nanocubes have high saturation magnetization value and exhibit superparamagnetic hysteresis loop.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Magnetic properties of Fe implanted SrTiO{sub 3} perovskite crystal

Graphical abstract: - Highlights: • The results of investigations of magnetic properties of Fe implanted SrTiO{sub 3} are presented. • The measurements of the temperature dependence of the magnetization were performed. • Ferromagnetic hysteresis loops in Fe implanted SrTiO{sub 3} were observed at low temperatures. • Superparamagnetic behavior of the samples at high temperatures was revealed. • It was shown that the magnetization of the samples depends on the fluency of implantation. - Abstract: The results of investigations of magnetic properties of SrTiO{sub 3} perovskite crystal implanted with 40 keV Fe ions at the fluencies between 0.5 × 10{sup 17} and 1.5 × 10{sup 17} ion/cm{sup 2} are presented. It has been revealed that high-fluency implantation with Fe ions results in the formation of a granular metal particulate composite in the irradiated near-surface layer of SrTiO{sub 3} substrate, which exhibits remarkable ferromagnetic behavior. The measurements of the temperature dependence of the magnetic moment showed that the samples exhibit blocking temperature at about 350 K, above which a superparamagnetic behavior has been observed. Ferromagnetic ordering and magnetic hysteresis loops were observed in Fe implanted SrTiO{sub 3} at the temperatures lower than 350 K. It has been shown that the magnetization of the ferromagnetic state depends on the fluency of implantation.

36 MATERIALS SCIENCE↗
DOE OSTI2013

A chemical approach toward low temperature alloying of immiscible iron and molybdenum metals

Graphical abstract: - Highlights: • Low temperature pyrolysis of [Fe(bipy){sub 3}]Cl{sub 2} and [Mo(bipy)Cl{sub 4}] homogeneous powder. • Easy low temperature alloying of immiscible metals like Fe and Mo. • Uniform sized Fe–Mo nanoalloy with particle size of 48–68 nm. • Characterization by EDXRF, AFM, XRPD, magnetometery, {sup 57}Fe Mössbauer and impedance. • Alloy behaves as almost superparamagnetic obeying simple –R(CPE)– circuit. - Abstract: The present research is based on a low temperature operated feasible method for the synthesis of immiscible iron and molybdenum metals’ nanoalloy for technological applications. The nanoalloy has been synthesized by pyrolysis of homogeneous powder precipitated, from a common solvent, of the two complexes, trisbipyridineiron(II)chloride, [Fe(bipy){sub 3}]Cl{sub 2}, and bipyridinemolybedenum(IV) chloride, [Mo(bipy)Cl{sub 4}], followed by heating at 500 °C in an inert atmosphere of flowing argon gas. The resulting nanoalloy has been characterized by using EDXRF, AFM, XRD, magnetometery, {sup 57}Fe Mössbauer and impedance spectroscopies. These results showed that under provided experimental conditions iron and molybdenum metals, with known miscibility barrier, alloy together to give (1:1) single phase material having particle size in the range of 48–66 nm. The magnetism of iron is considerably reduced after alloy formation and shows its trend toward superparamagnetism. The designed chemical synthetic procedure is equally feasible for the fabrication of other immiscible metals.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Microwave-polyol controlled synthesis and magnetic properties of monodisperse Co{sub x}Ni{sub 1−x}Fe{sub 2}O{sub 4}/MWCNT nanocomposites

Graphical abstract: - Highlights: • Microwave-polyol preparation of monodisperse Co{sub x}Ni{sub 1−x}Fe{sub 2}O{sub 4}/MWCNT nanocomposites. • The composition is controlled through adjusting atomic ratios of Co and Ni salts. • Ms increases with increasing Co content. Hc is zero exhibiting superparamagnetic. - Abstract: Monodisperse Co{sub x}Ni{sub 1−x}Fe{sub 2}O{sub 4} nanoparticles (x = 0, 0.2, 0.4, 0.5, 0.6, 0.8, and 1) with controllable composition attached on the multi-walled carbon nanotubes (MWCNTs) were prepared by microwave-polyol method. The composition of Co{sub x}Ni{sub 1−x}Fe{sub 2}O{sub 4} nanoparticles can be controlled through adjusting the atomic ratios of cobalt and nickel nitrate in the mixed solution. The influence of the microwave power and microwave irradiation time on the monodispersion of nanoparticles was also investigated. The results show quasi-spherical Co{sub x}Ni{sub 1−x}Fe{sub 2}O{sub 4} nanoparticles with the face-centered cubic structure and average crystallite size (6 nm) are uniformly dispersed on MWCNTs. The saturation magnetization of Co{sub x}Ni{sub 1−x}Fe{sub 2}O{sub 4}/MWCNT nanocomposites increases gradually from 12.90 to 20.03 emu/g with increasing Co{sup 2+} concentration. The coercivity is almost zero at room temperature, which indicates the superparamagnetic behavior.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Electron spin resonance study of the La{sub 0.8}Sr{sub 0.2}MnO{sub 3} nanoparticle-decorated carbon nanotubes

Graphical abstract: Inverse spin susceptibilities obtained by integration of the distinct ESR line components of the LSMO-CNTs system as a function of temperature. - Highlights: • Spin/charge dynamics in La{sub 0.8}Sr{sub 0.2}MnO{sub 3}-decorated CNTs studied by EPR. • One spin species revealed only paramagnetic–superparamagnetic phase transition. • Another spin species manifested reflected weak localization of spin/charge carriers. • Spins participating in the magnetic phase transition and the itinerant spins well separated by EPR. - Abstract: We have studied La{sub 0.8}Sr{sub 0.2}MnO{sub 3} (LSMO) nanoparticle-decorated carbon nanotubes (CNTs) by means of the electron spin resonance (ESR) spectroscopy in view of our previous work on the magnetic and electrical properties of the system. One of the line components of the ESR spectrum reflected a paramagnetic–superparamagnetic phase transition at T{sub SP}∼200 K, which is accompanied by a concomitant metal–insulator transition (MIT) associated with charge transport taking place through the CNTs network triggered by the LSMO nanoparticles. On the other hand, another ESR line component revealed anomalies at T{sub WL}∼170 K as well, attributable to a 2D weak localization effect of the spin/charge carriers. Thus, magnetic interactions and dynamics of the distinct spin species were sensitively reflected in the LSMO-CNTs system.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Ferrous sulfate based low temperature synthesis and magnetic properties of nickel ferrite nanostructures

Highlights: • Novel low temperature synthesis of nickel ferrite nanoparticles. • Comparison with two conventional synthesis techniques including hydrothermal method. • XRD results confirm the formation of crystalline nickel ferrites at 110 °C. • Superparamagnetic particles with applications in drug delivery and hyperthermia. • Magnetic properties superior to conventional methods found in new process. - Abstract: We report a simple, low temperature and surfactant free co-precipitation method for the preparation of nickel ferrite nanostructures using ferrous sulfate as the iron precursor. The products obtained from this method were compared for their physical properties with nickel ferrites produced through conventional co-precipitation and hydrothermal methods which used ferric nitrate as the iron precursor. X-ray diffraction analysis confirmed the synthesis of single phase inverse spinel nanocrystalline nickel ferrites at temperature as low as 110 °C in the low temperature method. Electron microscopy analysis on the samples revealed the formation of nearly spherical nanostructures in the size range of 20–30 nm which are comparable to other conventional methods. Vibrating sample magnetometer measurements showed the formation of superparamagnetic particles with high magnetic saturation 41.3 emu/g which corresponds well with conventional synthesis methods. The spontaneous synthesis of the nickel ferrite nanoparticles by the low temperature synthesis method was attributed to the presence of 0.808 kJ mol{sup −1} of excess Gibbs free energy due to ferrous sulfate precursor.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Amorphous iron–chromium oxide nanoparticles with long-term stability

Highlights: • Fe–Cr oxide nanoparticles with pre-established metals ratio were obtained. • The amorphous state and its long-term stability were highlighted by X-ray diffraction. • The average diameter of dried nanoparticles was 3.5 nm, as was estimated by TEM, AFM. • In hexane dispersion, nanoparticles with diameter in the range 2.33–4.85 nm were found. • Superparamagnetic state of NPs co-exists with diamagnetism of the organic layer. - Abstract: Iron–chromium nanoparticles (NPs) were obtained through the thermal decomposition of μ{sub 3}-oxo heterotrinuclear (FeCr{sub 2}O) acetate in the presence of sunflower oil and dodecylamine (DA) as surfactants. The average diameter of the NPs was 3.5 nm, as estimated on the basis of transmission electron microscopy and atomic force microscopy images. Both techniques revealed the formation of roughly approximated spheres with some irregularities and agglomerations in larger spherical assemblies of 50–100 nm. In hexane, NPs with diameters in the 2.33–4.85 nm range are individually dispersed, as emphasized by dynamic light scattering measurements. The amorphous nature of the product was emphasized by X-ray powder diffraction. The study of the magnetic properties shows the presence of superparamagnetic state of iron–chromium oxide NPs and the diamagnetic contribution from DA layer forming a shell of NPs.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2016

Synthesis and magnetic properties of bundled and dispersed Co{sub 3}O{sub 4} nanowires

Highlights: • Co{sub 3}O{sub 4} nanowires possessed the same diameter and the different interwires distance. • All samples possessed antiferromagnetism and superparamagnetism at high temperature. • The exchange bias effect was observed at low temperature. • The surface spin coupling restrained the surface effect of magnetic nanostructures. - Abstract: The magnetic Co{sub 3}O{sub 4} nanowires were synthesized using the templates of SBA-15, and then the well-dispersed nanowires (D-wires) were separated from the bundled ordered nanowires (B-wires) with the centrifugal technique. TEM images indicated that D-wires were highly dispersed Co{sub 3}O{sub 4} nanowires and B-wires existed in bundles. All samples possessed the antiferromagnetism and superparamagnetism at high temperature. After revealing the intrinsic magnetic properties of Co{sub 3}O{sub 4} nanowires with D-wires, the magnetic behavior of B-wires was discussed in detail, and then the magnetic interaction between neighboring nanowires could be deduced. The exchange bias effect from the body Co{sub 3}O{sub 4} antiferromagnetism and surface ferromagnetism was observed at low temperature. The magnetization of B-wires was higher than that of D-wires, which was attributed to the constraint of the surface spin coupling between the neighboring nanowires to the surface affect of nanostructures.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Quaternary M{sub 0.25}Cu{sub 0.25}Mg{sub 0.5}Fe{sub 2}O{sub 4} (M = Ni, Zn, Co, Mn) ferrite oxides: Synthesis, characterization and magnetic properties

Highlights: • Superparamagnetic quaternary nanoferrite (M{sub 0.25}Cu{sub 0.25}Mg{sub 0.5}Fe{sub 2}O{sub 4,} where M = Mn, Zn, Co, Ni) were obtained. • C, O, H and metals were observed by XPS analysis. • Phases purity were confirmed by XRD diffraction and crystallite size (3–10 nm) were determind. - Abstract: We report the synthesis of M{sub 0.25}Cu{sub 0.25}Mg{sub 0.5}Fe{sub 2}O{sub 4} (where M = Mn, Zn, Co, Ni) nanoparticles using the coprecipitation method in the presence of carboxymethyl cellulose (CMC) as the in-situ surfactant. The crystalline structure and surface morphology were examined by means of X-ray diffraction (XRD) and scanning electron microscopy (SEM) and it was established that the average diameter of the magnetic nanoparticles (MNPs) is in the range of 3–10 nm. X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) show that the MNPs are activated by the hydrophilic groups of the surfactant, which coat them and enhance their stability. The vibrating sample magnetometry measurements show the superparamagnetic behavior of the nanoparticles. Due to their small crystallite size, which implies large surface area, and their functionalization with organic groups, the obtained nanoparticles could have medical and catalytic applications.

36 MATERIALS SCIENCE↗
DOE OSTI2017

Controlled synthesis and magnetic properties of Ni nanotubes and nanowires

Graphical abstract: TEM images of the as-prepared Ni nanotubes and nanowires. - Highlights: • Ni nanotubes and nanowires are synthesized by a convenient sol-gel autocombustion method with the assistance of AAO templates. • The products having tubular or wire-like morphologies can be perfectly controlled by adjusting the experimental conditions. • The synthetic mechanism is discussed. • Magnetic measurements indicate that both the Ni nanotubes and the Ni nanowires possess superparamagnetism at room temperature. - Abstract: Ni nanotubes and nanowires with an average diameter of about 140 nm are synthesized by a template-assisted sol-gel autocombustion method using nickel nitrate, citric acid and ammonia as the starting materials. The anodic aluminum oxide templates are prepared by a facile anodizing method. By adjusting the experimental conditions in the sol-gel process, the final products having tubular or wire-like morphologies can be perfectly controlled. Transmission electron microscope characterization indicates that the Ni nanotubes are very friable and can be easily broken into pieces of short nanotubes, but the Ni nanowires are compact and have very high aspect ratios. Magnetic measurements indicate that both the Ni nanowires and the Ni nanotubes possess superparamagnetism at room temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Magnetic nanoparticles formed in glasses co-doped with iron and larger radius elements

A new type of nanoparticle-containing glasses based on borate glasses co-doped with low contents of iron and larger radius elements, Dy, Tb, Gd, Ho, Er, Y, and Bi, is studied. Heat treatment of these glasses results in formation of magnetic nanoparticles, radically changing their physical properties. Transmission electron microscopy and synchrotron radiation-based techniques: x-ray diffraction, extended x-ray absorption fine structure, x-ray absorption near-edge structure, and small-angle x-ray scattering, show a broad distribution of nanoparticle sizes with characteristics depending on the treatment regime; a crystalline structure of these nanoparticles is detected in heat treated samples. Magnetic circular dichroism (MCD) studies of samples subjected to heat treatment as well as of maghemite, magnetite, and iron garnet allow to unambiguously assign the nanoparticle structure to maghemite, independently of co-dopant nature and of heat treatment regime used. Different features observed in the MCD spectra are related to different electron transitions in Fe{sup 3+} ions gathered in the nanoparticles. The static magnetization in heat treated samples has non-linear dependence on the magnetizing field with hysteresis. Zero-field cooled magnetization curves show that at higher temperatures the nanoparticles occur in superparamagnetic state with blocking temperatures above 100 K. Below ca. 20 K, a considerable contribution to both zero field-cooled and field-cooled magnetizations occurs from diluted paramagnetic ions. Variable-temperature electron magnetic resonance (EMR) studies unambiguously show that in as-prepared glasses paramagnetic ions are in diluted state and confirm the formation of magnetic nanoparticles already at earlier stages of heat treatment. Computer simulations of the EMR spectra corroborate the broad distribution of nanoparticle sizes found by 'direct' techniques as well as superparamagnetic nanoparticle behaviour demonstrated in the magnetization studies.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2014

MnBi particles with high energy density made by spark erosion

We report on the properties of low-temperature phase (LTP)-MnBi particles produced by the rapid-quenching technique of spark-erosion. The as-prepared powder consists of amorphous, crystalline, and superparamagnetic particles, mostly as porous aggregates. The major fraction of the powder consists of 20–30 nm particles. A short anneal crystallizes the amorphous particles producing a high moment, >90% of theoretical M{sub S}, albeit with H{sub C} of a few kOe. If lightly milled, the agglomerates are broken up to yield H{sub C} of 1 T. These findings are supported by the x-ray diffraction pattern showing broadened peaks of the predominant LTP-MnBi phase. The combination of spark erosion, milling, and annealing has produced randomly oriented particles with (BH){sub MAX} ∼ 3.0 MGOe. The particles are expected to show record energy product when aligned along their crystallographic easy axes.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Evidence for spin glass state of NdCo{sub 1−x}Ni{sub x}O{sub 3} (x = 0.3−0.5)

Low-temperature magnetic properties of single phase NdCo{sub 1−x}Ni{sub x}O{sub 3}(x = 0.3−0.5) have been studied using ac and dc magnetic susceptibility measurements. Nickel substituted samples have been found to exhibit a different magnetic state at low temperature as compared to pristine NdCoO{sub 3}. The temperature dependent dc magnetization M (T) revealed the presence of a sharp cusp occurring at characteristic temperatures T{sub P}, for x = 0.3, 0.4, 0.5. Below T{sub P}, clear effect of magnetic field can be seen in M (T) curves and T{sub P} decreases with increasing magnetic field as well as Ni substitution content. The isothermal magnetization measurements at low temperatures shows small unsaturated hysteresis loop at lowest temperature (10 K). The ac susceptibility results show a clear frequency dependent feature. These results are analyzed to distinguish superparamagnetic and spin glass behavior by using Néel-Arrhennius, Vogel-Fulcher law, and power law fitting. This analysis ruled out the superparamagnet like state and suggests the presence of significant inter-cluster interactions, giving rise to spin-glass like cooperative freezing.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2014

Surface driven effects on magnetic properties of antiferromagnetic LaFeO{sub 3} nanocrystalline ferrite

LaFeO{sub 3} nanocrystalline ferrites were synthesized through sol-gel method in different size distributions and the effect of finite size on magnetic properties is investigated. Results of magnetization and Mössbauer measurements show that superparamagnetism and weak ferromagnetic behavior in some of the size distributions. The origin of the superparamagnetism is from fine particles similar to ferromagnetic single domains and the weak ferromagnetism comes from surface spin disorder caused by Dzyaloshinskii-Moriya interaction. The magnetic ground state of LaFeO{sub 3} nanoparticles differs from that of bulk, and the ground state is dictated by the finite size effect because density of states depends on the dimensionality of the sample.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Tuning of structural and magnetic properties of Mn-doped CoFe{sub 2}O{sub 4} nanoparticles

In the present manuscript, Mn{sub x}Co{sub 1-x}Fe{sub 2}O{sub 4} (x=0.0, 0.2, 0.4, 0.6, 0.8 and 1.0) nanoparticles have been synthesized with co-precipitation method by annealing at 900 °C and studied the structural and magnetic properties. X ray diffraction pattern reveals the formation of single phase cubic spinel structure with the space group Fd-3m. An impurity peak of α-Fe{sub 2}O{sub 3} has been observed in the XRD patterns of samples with Mn composition, x ≥ 0.4. However, this impurity phase of α-Fe{sub 2}O{sub 3} is not observed in the MnFe{sub 2}O{sub 4} sample synthesized by annealing at 500 °C. FESEM results indicate the formation of nano-sized particles. Magnetic measurements show ferrimagnetic interaction in Mn{sub x}Co{sub 1-x}Fe{sub 2}O{sub 4} (x≥0) nanoparticles at room temperature. However, MnFe{sub 2}O{sub 4} sample synthesized by annealing at 500 °C shows superparamagnetic behavior. We have fitted the M-H curve of MnFe{sub 2}O{sub 4} synthesized by annealing at 500 °C with modified Langvenin function to confirm superparamagnetism. The correlation between the structural and observed magnetic properties of as synthesized samples nanoparticles will be described and discussed in this paper.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗