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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 199 records · Page 11
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Magnetic and Structural Properties of Novel Neodymium-Tin Spinel Ferrite Nanoparticles

Novel spinel neodymium-tin ferrite nanoparticles (Nd{sub 0.5}Sn{sub 0.5}Fe{sub 2}O{sub 4}) have been synthesized by the coprecipitation method; x-ray diffraction (XRD), transmission electron microscopy (TEM), and superconducting quantum interference device magnetometer (SQUID) techniques were used to characterize the crystal structure, morphology, and magnetic properties. The spinel structure of a single phase is obtained according to XRD results. From TEM characterization results, we obtained a spherical morphology with an average of 13 nm. Magnetic measurement indicates that the nanoparticles have a superparamagnetic phase with a corresponding blocking temperature (T{sub B}) of about 360 K. These new nanomaterials can potentially be used in nanoelectronic devices, magnetic sensors, and hyperthermia application.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Structure and Magnetization of Polycrystalline La{sub 0.66}Ca{sub 0.33}MnO{sub 3} and La{sub 0.66}Ba{sub 0.33}MnO{sub 3} Films Prepared Using Sol-Gel Technique

The structure and static magnetization of polycrystalline La{sub 0.66}Ca{sub 0.33}MnO{sub 3} (LCMO) and La{sub 0.66}Ba{sub 0.33}MnO{sub 3} (LBMO) films grown on glass substrate using sol-gel technique have been investigated. X-ray diffraction (XRD) analysis revealed the average grain sizes of about 12 and 10 nm for granular LCMO and LBMO samples, respectively. The root mean square (RMS) surface roughness of about 100 nm has been obtained for both films by using scanning electron microscope (SEM) technique. The temperature dependences of the magnetization of LCMO and LBMO films registered in zero field cooling (ZFC) and field cooling (FC) regimes revealed a superparamagnetic state in both samples with remarkable distribution of blocking temperatures in a wide temperature interval, the average values of which have been estimated to be about 120 and 90 K for LCMO and LBMO, respectively. The average magnetic crystallite sizes obtained from the magnetizations studies coincide with the values revealed from the structural studies.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Preparation and Thermophysical Investigations of CoFe{sub 2}O{sub 4}-based Nanofluid: a Potential Heat Transfer Agent

Cobalt ferrite nanoparticles were synthesized by employing chemical co-precipitation technique. The structure, morphology, elemental composition, and magnetization studies of cobalt ferrite nanoparticles were carried by XRD, FE-SEM, EDS, and VSM techniques, respectively. Rietveld refined XRD pattern exhibited the single-phase cubic spinel structure with Fd-3m space group. FE-SEM images indicated some agglomeration of spherical grains which can be attributed to high surface energy and magnetic interactions. Presence of peaks of respective elements (Co, Fe, and O) in EDS spectrum showed formation of CoFe{sub 2}O{sub 4}. The M–H loop recorded at 300 K revealed superparamagnetic behavior and explained by fine particles size. The blocking temperature of the CoFe{sub 2}O{sub 4}nanoparticles from FC-ZFC curve was found to be 144 K. Cobalt ferrite–ethylene glycol nanofluids of various concentrations 0.0–1.0% in steps of 0.2% were prepared by ultrasonically assisted two-step technique. Thermophysical parameters such as thermal conductivity, specific heat, viscosity, and density were investigated as a function of both volume fraction and temperature. The experimental and theoretical value of each sample was correlated. The thermal conductivity was significantly enhanced with an increase in volume fraction and temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Effect of Ce{sup 3+} Ion on Structural and Hyperfine Interaction Studies of Co{sub 0.5}Ni{sub 0.5}Fe{sub 2−x}Ce{sub x}O{sub 4} Ferrites: Useful for Permanent Magnet Applications

Nanoparticles of Co{sub 0.5}Ni{sub 0.5}Fe{sub 2−x}Ce{sub x}O{sub 4} (where x = 0.0, 0.01, 0.015 and 0.02) ferrites are prepared by the modified solution combustion method using a mixture of fuels and are characterized to understand their structural, microstructural and magnetic properties. The X-ray diffraction is used to confirm the formation of a single-phase cubic spinel structure. The average crystallite sizes are calculated using the Scherrer formula and are found to be less than 50 nm. The microstructural features are obtained by the scanning electron microscopy, and the compositional analysis is done by using the energy-dispersive spectroscopy. The transmission electron microscopy (TEM) investigations show that the synthesized ferrites are made up of very fine spherical nanoparticles. The influence of a rare-earth element (Ce{sup 3+}) on the magnetic properties of the samples was studied using the Mössbauer spectroscopy. The Mössbauer spectroscopy reveals the formation of broadened Zeeman lines and quadrupole-split lines and the presence of the Fe{sup 3+} charge state at B sites in the samples. The quadrupole splitting shows that the orientation of the magnetic hyperfine field with respect to the principle axes of the electric field gradient was random. The magnetic hyperfine field values indicate that the A sites have more A-O-B superexchange interactions than the B sites. The coexistence of magnetic sextet and a doublet component on the room-temperature spectra suggests superparamagnetic properties of the nanoparticles. The low-temperature (15 K) Mössbauer spectroscopy explores the paramagnetic relaxation in the nanoparticles. The area under the sextet refers to Fe{sup 3+} concentrations in the tetrahedral and octahedral sites of the ferrite. This study confirms that the Ce{sup 3+} substitution of Fe{sup 3+} only for octahedron sites causes the decrease in Fe-O-Fe arrangement. The effect of Ce{sup 3+} doping on the magnetic properties of Co{sub 0.5}Ni{sub 0.5}Fe{sub 2}O{sub 4} is examined from the vibrating sample magnetometry (VSM) spectra. Saturation magnetization values are decreased initially and then increased, as result of Ce{sup 3+} doping. This can be explained by Neel’s two-sub-lattice model. Further, the value of coercivity is found to be increasing with increasing Ce{sup 3+} concentration. The obtained results of M-H loop with improved coercivity (from 851 to 1039 Oe) by Ce{sup 3+} doping of Co{sub 0.5}Ni{sub 0.5}Fe{sub 2}O{sub 4} demonstrate the usefulness for permanent magnet applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Anisometric Iron Oxide-Based Nanoparticles and Sols Based on Them: Preparation and Properties

We have synthesized magnetic powders of the magnetite-maghemite series by the chemical reaction of the FeSO{sub 4} iron salt and the natural arabinogalactan polysaccharide. These particles with a high magnetization value (∼ 300 Gs) represent a mixture of spherical particles and nanorods. Particles of a spherical shape (diameter of ∼ 5–6 nm) show a superparamagnetic behavior at room temperature, while rods with a diameter of ∼ 5 nm and a length of 30 nm are magnetic. We have prepared sol samples based on the nanoparticle aqueous solution of arabinogalactan. Our results on the magnetism of the circular dichroism (MCD) on sol are consistent with the of Mössbauer spectroscopy data.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

A Review on Iron Oxide Nanoparticles and Their Biomedical Applications

The iron oxide nanoparticles have a great attraction in biomedical applications due to their non-toxic role in the biological systems. The iron oxide nanoparticles have both magnetic behaviour and semiconductor property which lead to multifunctional biomedical applications. The iron oxide nanoparticles used in biomedical fields such as antibacterial, antifungal and anticancer were reviewed. The uses of hematite (α-Fe{sub 2}O{sub 3}), maghemite (γ-Fe{sub 2}O{sub 3}) and magnetite (Fe{sub 3}O{sub 4}) nanoparticles, for an inhibition time in biological activities, are listed in this work. Also, this review explains the use of iron oxide nanoparticles in the biomedical fields with particular attention to the application of hematite and superparamagnetic iron oxide nanoparticles. In this review, analysis reveals that the role of iron oxide in biological activity is good due to its biocompatibility, biodegradability, ease of synthesis and different magnetic behaviours. The change of properties of iron oxide nanoparticles such as particle size, morphology, surface, agglomeration and electronic properties has specific impact in biomedical application. The review mainly focused in and discussed about antibacterial, anticancer, bone marrow and cell labelling activities. From this review work, the iron oxide nanoparticle may be specialised in particular bacterial and cancer treatments. Also discussed are the iron oxide nanoparticle-specific biomedical applications like human placenta, insulin and retinal locus treatments.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2019

Influence of Ce{sup 3+} Ion Doping on Structural and Magnetic Properties of Magnesium Nanoferrite

Pure and rare earth ion Ce{sup 3+}-doped magnesium nanoferrite magnetic particles, i.e., MgFe{sub 2}O{sub 4} and MgCe{sub x}Fe{sub 2−x}O{sub 4} (x = 0.0, 0.025, 0.05, 0.075, and 0.1) were successfully fabricated using sol-gel technique, and qualitative studies were carried out using X-ray diffractometer (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), high-resolution field-emission scanning electron microscopy (HRFESEM) equipped with energy-dispersive spectroscopy (EDS), vibrating sample magnetometer (VSM), and electron paramagnetic resonance (EPR) techniques. X-ray diffraction analysis confirmed the crystalline phase of the synthesized samples with no extra phase. The crystallite size obtained from W-H plots follow the same trend as calculated using Scherrer method, and the strain decreases with increasing Ce{sup 3+} ion concentration indicating a lesser number of deformities. FTIR spectra revealed the shifting of lower-frequency band to the higher side with the larger radii Ce{sup 3+} ions. HRFESEM images reveal the reduction in stress on doping. No additional impurities are observed in synthesized samples as is confirmed by EDS analysis. The average particle size obtained by TEM are in agreement with XRD analysis. EPR studies showed an increase in g value and line width with doping. Magnetic measurements carried out at room temperature reveals the value of magnetization initially decreases up to x = 0.05 and afterwards increases with the addition of Ce{sup 3+} ions. These properties reveal superparamagnetic nature of cerium-doped magnesium nanoparticles and can be suitable for catalyst and humidity sensors.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Magnetic Properties of Mn-Substituted Zn–Mg- and Zn–Co-Nanosized Compounds

Mn-substituted Zn–Mg and Zn–Co with chemical formula Mn{sub 0.3}Mg{sub 0.2}TM{sub 0.5}Fe{sub 2}O{sub 4} (TM = Zn or Co) fine powders have been synthesized by glycol-thermal process. XRD results reveal the formation of a cubic phase without any impurity phases. TEM images show nearly spherical particles with fairly distributed particles with an average crystallite size of about 14 nm. {sup 57}Fe Mössbauer spectral studies show well-resolved magnetic splitting in the Mn–Mg–Co oxide due to stronger superexchange interactions. FC and ZFC magnetization data revealed the superparamagnetic nature of the compounds investigated. Mn–Mg–Zn nanoparticles are blocked at about 206 K while the maximum blocking temperature of Mn–Mg–Co-nanosized oxide is above 300 K. These differences were discussed on the basis of Stoner-Wohlfath relation T{sub B} = KV /25k{sub B}.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Effect of Zn, Ga and Gd Doping on Structural and Magnetic Properties of Nanonickel Ferrite Prepared by Two Different Methods

Zn/Ga/Gd-substituted NiFe{sub 2}O{sub 4} was formed by solid state reaction and citrate methods. The influence of substitutions on phase formation, the strain, crystallize size, cations distribution and magnetic properties have been examined by X-ray diffraction, Mössbauer effect spectrometer, Fourier-transform infrared, and vibrating sample magnetometer. Zn/Ga/Gd substituted NiFe{sub 2}O{sub 4} samples prepared by solid state method showed that as gadolinium introduced into the system, a second phase was formed with a small percentage while samples prepared by citrate method exhibited a single phase. The distributions of different cations between different sites were determined by both Mössbauer effect spectroscopy, modified Bertaut and Rietveld analysis. Mössbauer technique at room temperature showed that samples synthesized by the ceramic method have a magnetic order while samples prepared by citrate method have a superparamagnetic nature. The canting angle between magnetic ions was increased by increased the amount of Zn in samples prepared by both methods.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Magnetic Evaluation of the Nanoparticles Coated with Polyvinylpyrrolidone and Polyvinyl Chloride Nanoparticles Synthesized by Electro-deposition Method for Hyperthermia Application

Fe{sub 3}O{sub 4} nanoparticles, coated with polyvinylpyrrolidone (PVP) + polyvinyl chloride (PVC), were synthesized using cathodic electrochemical deposition (CED) technique. Physical properties of the uncoated and PVP + PVC-coated nanoparticles were investigated using several methods including X-ray diffraction (XRD), transmission electron microscopy (TEM), vibrating sample magnetometry (VSM), Fourier transform infrared (FT-IR), and AC susceptometer. In both the samples, single-phase formation in cubic spinel structure is detected in the XRD analysis. In this study, the mean crystallite size of the prepared specimens is found to be varied from 10.2 to 8.7 nm after PVP + PVC coating. The results of the FT-TR test thoroughly verified the existence of PVP/PVC layer onto the surface of the electrodeposited NPs, and magnetic results also confirmed a superparamagnetic (SPM) behavior at room temperature for both of them. Coercivity and magnetization saturation reduction have also been observed, despite having lower grain size. Also, weak magnetic interactions of inter-particle and a superspin glass-like behavior at low temperatures are confirmed. In addition, increasing of PVP + PVC content on the surface coating of the magnetic nanoparticles has decreased the inter-particle interactions.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Structural, Optical, Magnetic, and Dielectric Properties of Cr{sup 3+} Substituted Cobalt Aluminate Nanoparticles

The present study investigates the influence of Cr{sup 3+} substitution on structural, optical, dielectric, and magnetic properties of cobalt aluminates in the aluminates series CoAl{sub 2-x}Cr{sub x}O{sub 4}, 0.00 ≤ x ≤ 0.20. These series of nanoparticles are effectively synthesized using the co-precipitation method. The cubic spinel aluminate structure is confirmed by X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopic measurements. Transmission electron microscopy (TEM) analysis shows the formation of spherical nanoparticles, which are homogeneous in shape and size. The optical properties of the prepared samples have been investigated by means of optical absorbance spectra. The optical band gap E{sub opt}{sup i} and Urbach energy E{sub u} are estimated. At room temperature, the magnetization of undoped CoAl{sub 2}O{sub 4} reveals a weak ferromagnetic behavior. This ferromagnetism is increased for the sample with x = 0.05, and the samples with higher Cr{sup 3+} content have a tendency to be superparamagnetic on account of the formation of single-domain particles as a consequence of small particle size. Real part of dielectric constant (ε{sup ′}), dielectric loss (tanδ), ac conductivity (σ{sub ac}), real part of impedance (Z{sup ′}), and imaginary part of impedance (Z{sup ″}) are analyzed as a function of frequency and Cr{sup 3+} content. The results show that the dielectric loss (tanδ), dielectric permittivity (ε{sup ′}), and ac conductivity (σ{sub ac}) decrease with the increase in Cr{sup 3+} content, x = 0.05, and then increase with a further increase in Cr{sup 3+} content. The increase in these parameters has been explained on the basis of the hopping mechanism. From the Cole–Cole diagram, the value of the relaxation time τ can be calculated and it has been found to increase with increasing the Cr{sup 3+} content. Actually, a high dielectric constant makes these materials good for energy storage at high frequencies.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Hysteresis Cycle and Magnetization Behaviors of a Mixed-Spin (7/2, 3/2) Ferrimagnetic Ising Model: Monte Carlo Investigation

The effects of single-ion anisotropies and an external magnetic field on the magnetization of the mixed-spin (7/2, 3/2) ferrimagnetic Ising system are investigated within Monte Carlo simulation. Under certain values of the physical parameters, multiple hysteresis loop behaviors such as double, triple, and quintuple hysteresis cycles have been observed. Particularly, the superparamagnetic phase has been shown. The ground-state phase diagrams are presented.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Tracking of SPIONs in Barley (Hordeum vulgare L.) Plant Organs During its Growth

Barley plants were grown in water solutions containing nutrient elements and superparamagnetic iron oxide nanoparticles (SPIONs), particularly the magnetite nanoparticles (Fe{sub 3}O{sub 4}; 15–20-nm particle size). No visible detection of toxicity on plants’ growth had been observed. The different samples from two different organs of the plants, i.e., roots and leaves, were investigated using X-ray diffraction (XRD), bright-field microscope, and transmission electron microscope (TEM). To track the SPIONs, magnetic measurements using vibrating sample magnetometry (VSM) and Mössbauer spectroscopy at room temperature were also performed in the two different dried root and leaf organs of the plants. The magnetic signals measured in root and leaf organs clearly indicated an uptake of Fe{sub 3}O{sub 4} magnetic nanoparticles (MNPs) by the barley plant from aqueous medium containing Fe{sub 3}O{sub 4} MNPs and their subsequent accumulation in the plant organs. The different parameters such as hyperfine magnetic field, quadrupole splitting, isomer shift, and line width were deduced from Mössbauer spectroscopy data. The Mössbauer spectra are constituted of two magnetic sextets (A site, B site) and paramagnetic central doublet.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2019

Synthesis and Characterization of Hydrophobic Fe{sub 3}O{sub 4} Magnetic Nanoparticles with High Saturation Magnetization

A simple one-step solvothermal method is proposed to prepare hydrophobic Fe{sub 3}O{sub 4} nanoparticles (MNPs) using iron acetylacetonate (Fe(acac){sub 3}), oleylamine (OAm), and ethylene glycol (EG). X-ray powder diffraction, scanning electron microscope, infrared spectroscopy, transmission electron microscopy, X-ray photoelectron spectrometry, and vibrating sample magnetometer are used to characterize the structure, morphology, and properties of products. The testing results indicate that the as-synthesized products are spherical-like hydrophobic MNPs, superparamagnetic at room temperature, with a saturation magnetization up to 76.8 emu/g. The good hydrophobic property of MNPs is attributed to the coverage of oleylamine, without causing a remarkable loss of magnetic property. In addition, the influences of material ratio, aging time, oleic acid, and stearic acid used as additives are studied in our research.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Prominent Study on Surface Properties and Diffusion Coefficient of Urease-Conjugated Magnetite Nanoparticles

Herein, the magnetite nanoparticles (MNs) were prepared by facile solvothermal method and its porous nature was modified using 3-(2-aminoethyl)-3-aminopropyl trimethoxysilane (AEAPS). Magnetite formation, successful amino tagging, and urease conjugation on the surface were confirmed from the presence of certain functional groups in Fourier transform infrared (FT-IR) spectra. Also, nanosize (13.2 nm) and spherical morphology of MNs were evaluated from diffraction patterns and electron micrographs respectively. Lower retentivity and coercivities in magnetization curve revealed the superparamagnetic behavior, and nitrogen adsorption/desorption curves exhibited decrease in its surface porosity. Conductivity measurements showed lower diffusion coefficient (D{sub e} = 1.9 × 10{sup −17} cm{sup 2}/min) and higher diffusion with limited hydrolytic reaction in native urease and improved activity of conjugated urease with higher D{sub e} (12.62 × 10{sup −16} cm{sup 2}/min). Hence, this study revealed that the surface porous nature of MNs can be altered effectively by amino tagging in order to overcome diffusional limitations thereby enhancing enzyme activity.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2011

Tumor-targeting magnetic lipoplex delivery of short hairpin RNA suppresses IGF-1R overexpression of lung adenocarcinoma A549 cells in vitro and in vivo

Highlights: {yields} We compared lipofection with magnetofection about difference of transfection efficiency on delivery a therapeutic gene in vitro and in vivo. {yields} We investigated the difference of shRNA induced by magnetofection and lipofection into A549 cell and subcutaneous tumor to knockdown IGF-1R overexpressed in A549 cell and A549 tumor. {yields} We investigated in vivo shRNA silenced IGF-1R overexpression 24, 48, and 72 h after shRNA intravenous injection into tumor-bearing mice by way of magnetofection and lipofection. {yields} Our results showed that magnetofection could achieve therapeutic gene targeted delivery into special site, which contributed to targeted gene therapy of lung cancers. -- Abstract: Liposomal magnetofection potentiates gene transfection by applying a magnetic field to concentrate magnetic lipoplexes onto target cells. Magnetic lipoplexes are self-assembling ternary complexes of cationic lipids with plasmid DNA associated with superparamagnetic iron oxide nanoparticles (SPIONs). Type1insulin-like growth factor receptor (IGF-1R), an important oncogene, is frequently overexpressed in lung cancer and mediates cancer cell proliferation and tumor growth. In this study, we evaluated the transfection efficiency (percentage of transfected cells) and therapeutic potential (potency of IGF-1R knockdown) of liposomal magnetofection of plasmids expressing GFP and shRNAs targeting IGF-1R (pGFPshIGF-1Rs) in A549 cells and in tumor-bearing mice as compared to lipofection using Lipofectamine 2000. Liposomal magnetofection provided a threefold improvement in transgene expression over lipofection and transfected up to 64.1% of A549 cells in vitro. In vitro, IGF-1R specific-shRNA transfected by lipofection inhibited IGF-1R protein by 56.1 {+-} 6% and by liposomal magnetofection by 85.1 {+-} 3%. In vivo delivery efficiency of the pGFPshIGF-1R plasmid into the tumor was significantly higher in the liposomal magnetofection group than in the lipofection group. In vivo IGF-1R specific-shRNA by lipofection inhibited IGF-1R protein by an average of 43.8 {+-} 5.3%; that by liposomal magnetofection inhibited IGF-1R protein by 43.4 {+-} 5.7%, 56.3 {+-} 9.6%, and 72.2 {+-} 6.8%, at 24, 48, and 72 h, respectively, after pGFPshIGF-1R injection. Our findings indicate that liposomal magnetofection may be a promising method that allows the targeting of gene therapy to lung cancer.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

Nanomedicine for the molecular diagnosis of cardiovascular pathologies

Predicting acute clinical events caused by atherosclerotic plaque rupture remains a clinical challenge. Anatomic mapping of the vascular tree provided by standard imaging technologies is not always sufficient for a robust diagnosis. Yet biological mechanisms leading to unstable plaques have been identified and corresponding biomarkers have been described. Nanosystems charged with contrast agents and targeted towards these specific biomarkers have been developed for several types of imaging modalities. The first systems that have reached the clinic are ultrasmall superparamagnetic iron oxides for Magnetic Resonance Imaging. Their potential relies on their passive accumulation by predominant physiological mechanisms in rupture-prone plaques. Active targeting strategies are under development to improve their specificity and set up other types of nanoplatforms. Preclinical results show a huge potential of nanomedicine for cardiovascular diagnosis, as long as the safety of these nanosystems in the body is studied in depth. - Highlights: • Ischemic stroke and myocardial infarction are the main causes of death in the world. • Their prevalence is related to late detection of high-risk atherosclerotic plaques. • Biomarkers of atherosclerosis evolution and potential ligands have been identified. • Nanosystems based on these ligands appear promising for early molecular diagnosis. • Preclinical and clinical nanosystems for common imaging modalities are described.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2011

Cation distribution and particle size effect on Raman spectrum of CoFe{sub 2}O{sub 4}

Moessbauer and Raman spectroscopic studies were carried out on CoFe{sub 2}O{sub 4} particles synthesized with size ranging from 6 to 500 nm (bulk). Cation distribution studies were carried out on the high temperature and room temperature phases of the microcrystalline CoFe{sub 2}O{sub 4} by Moessbauer and Raman spectroscopic methods. The high temperature phase of CoFe{sub 2}O{sub 4} showed a decreased inversion parameter of 0.69 as compared to the value of the room temperature phase of 0.95, indicating that the structure gradually transforms towards a normal spinel. Corresponding Raman spectra for these two phases of CoFe{sub 2}O{sub 4} showed a change in relative peak intensity of the vibrational mode at 695 cm{sup -1}(A{sub 1g}(1)) to 624 cm{sup -1} (A{sub 1g}(2)). The relative peak intensity ratio, I{sub v} between the A{sub 1g}(1) and A{sub 1g}(2) vibrational mode was decreasing with lowering of inversion parameter of the CoFe{sub 2}O{sub 4} spinel system. A variation of laser power on the sample surface was reflected in the cation distribution in ferrite phase. Superparamagnetic, single domain CoFe{sub 2}O{sub 4} particles (6 nm) showed a 20 cm{sup -1} red shift and broadening of phonon modes when compared to the macro-crystalline CoFe{sub 2}O{sub 4} (500 nm). Variation of Raman shift with particle size was studied by considering the bond polarization model. Raman spectroscopic studies clearly indicate the variation in the cation distribution in nano-sized particles and distribution tending to a normal spinel structural configuration. -- Graphical abstract: Variation of Raman shift difference ({Delta}{omega}) with size. Display Omitted

77 NANOSCIENCE AND NANOTECHNOLOGY↗