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Undoped and calcium substituted hematite (α-Fe₂O₃) nanoparticles are synthesized by surfactant-directed co-precipitation and post annealing method. The annealed nanoparticles were found to be in single phase in nature and crystallize in the rhombohedral structure with space group R3c as confirmed by Rietveld refinement of the X-ray diffraction (XRD) data. Average crystallite sizes are calculated to be 20 to 30 nm and 50 to 60 nm for the nanoparticles annealed at 400 and 600 °C respectively. Mossbauer spectra for all the nanoparticles could be fitted with a sextet corresponding to the single magnetic state of the iron atoms in its Fe³⁺ state in the hematite matrix. The FTIR and Raman spectra of all the samples correspond to specific modes of α-Fe₂O₃. UV-Vis spectra of annealed samples showed broad peaks in the range of 525-630 nm resulting from spin-forbidden ligand field transition together with the spin-flip transition among the 2t₂g states. The estimated band gap energies were in the range of 1.6 to 1.9 eV which are much lower than the reported values for nano hematite. From the room temperature magnetic hysteresis loop measurements, weak ferromagnetic behavior is observed in all undoped and Ca²⁺ doped hematite samples. Morin temperature (T(M)) is calculated to be 257 and 237 K for 1.45% doped samples with particle size 54 and 27 nm respectively. The sample with Ca content of 1.45 wt% when annealed at 400 °C showed that the particles were of different shapes which included both quasi spherical and rod shaped. On annealing the same sample at 600 °C, the nanorods collapsed to form bigger spherical and ellipsoidal particles.

Mn-doped NiO nanoparticles of the series Ni 1− x Mn x O ( x =0.00, 0.02, 0.04 and 0.06) are successfully synthesized using a low temperature hydrothermal method. Samples up to 6% Mn-doping are single phase in nature as observed from powder x-ray diffraction (XRD) studies. Rietveld refinement of the XRD data shows that all the single phase samples crystallize in the NaCl like fcc structure with space group Fm-3m . Unit cell volume decreases with increasing Mn-doping. Pure NiO nanoparticles show weak ferromagnetism, may be due to nanosize nature. Introduction of Mn within NiO lattice improves the magnetic properties significantly. Room temperature ferromagnetism is found in all the doped samples whereas the magnetization is highest for 2% Mn-doping and then decreases with further doping. The ZFC and FC branches in the temperature dependent magnetization separate well above 350 K indicating transition temperature well above room temperature for 2% Mn-doped NiO Nanoparticle. The ferromagnetic Curie temperature is found to be 653 K for the same sample as measured by temperature dependent magnetization study using vibrating sample magnetometer (VSM) in high vacuum.

The nano-porous LiFe₀.₉M₀.₁P₂O₇ (M = Fe, Co, Mn, Ni) particles were successfully prepared by simple microwave assisted combustion method and studied its detailed physico-chemical properties. The phase purity, crystallinity, functional group identification was revealed through X-ray diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) analysis. The presence of nanoporous was identified through transmission electron microscopic (TEM) images. The electrical conductivity results illustrated that LiFe₀.₉Ni₀.₁P₂O₇ has higher conductivity (2.85 x 10⁻⁷ S cm⁻¹) among the studied systems owing to their negligible grain boundary effect. The normal dielectric behaviour was observed for all the LiFe₀.₉M₀.₁P₂O₇ (M = Fe, Co, Mn, Ni) materials. The paramagnetic behaviour and the Fe³⁺ state of LiFe₀.₉M₀.₁P₂O₇ were obtained from VSM and Mossbauer spectral analysis respectively. The cyclic voltammogram suggested that the good electrochemical lithium intercalation/de-intercalation behaviour of LiFe₀.₉M₀.₁P₂O₇ (M = Fe, Co, Mn, Ni) electrodes in aqueous electrolytes. The obtained diffusion coefficient value is comparable with carbon based materials.

Samarium orthoferrite (SmFeO3) is synthesized by a simple combustion method using aspartic acid as fuel. Phase purity and functional groups are analyzed via X-ray diffraction (XRD) and Fourier transform infrared (FT-IR) analysis, which confirms the single phase formation of orthorhombic SmFeO3. Approximately spherical particles with size range 150-300 nm is revealed by scanning electron microscope (SEM). The conductivity of the material is identified by the single semicircle obtained in the solid state impedance spectra at elevated temperatures. The calculated electrical conductivity increases with increasing temperature, inferring the semiconducting nature of SmFeO3. A magnetic study at room temperature revealed weak ferromagnetic behaviour in SmFeO3 due to Dzyaloshinsky-Moriya antisymmetric exchange interaction mechanism. Mossbauer analysis confirmed the +3 oxidation state of iron and magnetic ordering of the sample at room temperature.

Here, we report on the enhancement in the magnetic properties of polycrystalline Bi1−xBaxFeO3 (x = 0.0, 0.05, 0.1 and 0.2) ceramic samples as a consequence of mechanical activated solid-state-reaction in comparison to standard solid-state-reaction processed samples. Our results suggest that mechanical activation has pronounced effect on the temperature of phase evolution as well as magnetic characteristics of Ba doped BiFeO3. The temperature, at which perovskite phase crystallizes is lower for mechanical activation assisted samples than for standard solid-state-reaction processed samples, attributed to pre-alloying during mechanical activation process. All the samples crystallize in a distorted perovskite structure with space group R3c and no structural change is found up to highest Ba doping. Mechanical activation also leads to significantly altered magnetic properties, particularly in higher Ba-doping samples which show about 50% increase in the magnetization and more than three fold increase in the coercive field. Local magnetic behavior investigated by 57Fe Mossbauer spectroscopy rules out any valence fluctuations of Fe and the hyperfine field corroborates the magnetization data.

Nanocrystalline spinel cobalt ferrite particles are synthesized by simple combustion method using aspartic acid and glycine as fuels. The single phase cubic structure of CoFe 2 O 4 is revealed through X-ray diffraction analysis (XRD). Further the Rietveld refinement confirms the formation of inverse spinel structure of CoFe 2 O 4 . The characteristic functional groups of Co–O and Fe–O are identified from Fourier Transform Infrared (FT-IR) analysis. Uniform distribution of of nearly spherical particles with the size range of 40–80 nm is identified through field emission scanning electron microscope (FESEM) images. The calculated DC conductivity is 1.469 × 10 −7 and 2.214 × 10 −8 S cm −1 , for CoFe 2 O 4 synthesized using aspartic acid and glycine, respectively. The dielectric behavior obeys the Maxwell–Wagner interfacial polarization. The ferromagnetic behavior of CoFe 2 O 4 is identified using VSM analysis and the calculated coercivity is 27 Oe and saturation magnetization is 68 emu/g.

We report systematic investigations on structural and magnetic properties of nanosized NiO powders prepared by the ball milling process followed by systematic annealing at different temperatures. Both as-milled and annealed NiO powders exhibit face centered cubic structure, but average crystallite size decreases (increases) with increasing milling time (annealing temperature). Pure NiO exhibits antiferromagnetic nature, which transforms into ferromagnetic one with moderate moment at room temperature with decreasing crystallite size. The on-set of ferromagnetic behavior in the as-milled powders was observed at higher temperatures (>750 K) as compared to bulk Ni (~630 K). On the other hand, annealing of as-milled powders showed a large reduction in magnetic moment and the rate of decrease of moment strongly depends on the milling conditions. The observed properties are discussed on the basis of crystallite size variation, defect density, oxidation/reduction of Ni and interaction between uncompensated surfaces and particle core with lattice expansion.

Lithium-based ferrites are promising and potential magnetic materials for microwave applications. They possess a spinel (AB 2 O 4 ) type crystal structure, where the distributions of metal cations over the tetrahedral (A) and octahedral (B) voids play a crucial role for exhibiting different physical properties. Among various parameter of synthesis, pH is an important factor that influences the cation distribution over A and B voids, overall growth of the nanoparticles and different physical properties. In the present work single phase Cr substituted lithium ferrite nanoparticles have been synthesized by the sol–gel method at different pH. The phase identification and crystallite size have been probed by X-ray diffraction studies. The crystallite size changes by 44.2–48.8 nm upon varying the pH from 3.5 to 11.5. In order to investigate the cations distribution at A/B sites, Mossbauer spectroscopic measurements were done. The values of magnetic hyperfine field obtained from the Mossbauer data for the A and B sites are ≈49.5 T and 51 T, respectively. Moreover, it is observed that the area ratio of B site to A site increases with increasing the pH. This observation further suggests that the B site is more preferable for Fe 3+ cations at higher pH than the A site. The magnetic parameter such as saturation magnetization ( M s ), remanent magnetization ( M r ), coercive field ( H C ) and squareness ( S ) are determined by vibrating sample magnetometer (VSM) measurements, which show a consistent increase with increasing pH. The reason for the variation in magnetic properties has been explained on the basis of increased Fe 3+ cation occupancies at the B site and size effect, which is well supported by Mossbauer spectroscopic and XRD studies.

In this work, we have explored the effect of surface functionalization in ZnO:Fe nanostructures. The ZnO:Fe nanostructures (NS), synthesized through hydrothermal route, have been surface functionalized (capped) by Tri-n-butylamine (amine). These samples have been characterized by X-ray diffraction (XRD), photoluminescence (PL) and Fourier transform infrared spectroscopy (FTIR). Field emission scanning electron microscopy (FESEM) and transmission electron microscope (TEM) illustrate that obtained nanostructures are high aspect ratio nanorods. Room temperature Mossbauer spectra (MS) of the samples indicate the presence of paramagnetic iron state i.e. Fe3+ in ZnO host. The ferromagnetic (FM) behavior of the samples was investigated by vibrating sample magnetometer (VSM) which shows that the significant enhancement of saturation magnetization in amine capped ZnO:Fe samples. This observed/enhanced ferromagnetism has been explained in terms of modification in the ZnO conduction band. The enhanced ferromagnetism due to surface functionalization has been justified by XRD, PL, FTIR and MS.

Using two different fuels such as aspartic acid and glycine, the spinel zinc ferrite nanoparticles were synthesized by the combustion method at different pH values. The thermochemical calculations for both the fuel assisted materials and its adiabatic flame temperature were calculated. The X-ray diffraction (XRD) pattern revealed the formation of single phase ZnFe 2 O 4 with high crystallinity. The characteristic functional groups of Fe3O and Zn3O were identified through FTIR analysis. Uniform size distribution of spherical particle in the average size range of 35–100 nm was inferred from SEM images. The room temperature DC conductivities of ZnFe 2 O 4 particles prepared by using aspartic and glycine are in the order of 10 −7 and 10 −8 respectively. The dielectric spectral analysis inferred that the obtained dielectric constant is high at low frequency and decreases with increase in frequency. This dielectric behavior is in accordance with the Maxwell–Wagner interfacial polarization. VSM and Mossbauer analysis revealed that the prepared material exhibits paramagnetic behavior and Fe 3+ state of iron content in ZnFe 2 O 4 at room temperature.

The present investigation describes the evolution of nano iron oxide/oxyhydroxide phases synthesized under identical conditions of precipitation using different starting reagents. Depending on the Fe(III) source and the neutralizing agent, single-phased nanogoethite, single-phased ferrihydrite and a combination of goethite, hematite and ferrihydrite phases were evolved in the synthesized samples. The prepared precursors were annealed at 400, 600 and 800 °C to study the changes in the morphology, optical and magnetic properties of single phase α-Fe2O3. Detailed characterization studies of the precursors and hematite obtained by annealing the samples were carried out using X-ray diffraction (XRD), Transmission electron microscopy (TEM), Raman and Mossbauer spectroscopy. Raman spectra of α-Fe2O3 obtained upon annealing the precursors showed changes in peaks' positions and intensities. These changes have been attributed to surface defects, the phonon confinement effect, the particle shape, and surface morphology. TEM images of the as-synthesized and annealed samples clearly showed differences in the shape, size and crystallinity. The direct and indirect band gap energies of annealed samples estimated from UV-vis absorption spectra showed these values to be smaller as compared to the bulk value for α-Fe2O3. The band gaps were not much affected by the nature of the precursor for the formation of α-Fe2O3 but did depend on annealing temperature. Very interesting trends were observed for the magnetic behaviour of α-Fe2O3. The coercivity values varied in the range of 28.7 to 2966 Oe. Probable mechanisms of formation of different phases have been outlined.

Ultrafine (2-5 nm) particles of amorphous Ca-Mg co-doped ferrihydrite have been synthesized by surfactant mediated co-precipitation method. The evolution of the amorphous ferrihydrite by Ca-Mg co-doping is quite different from our earlier investigations on individual doping of Ca and Mg. Amorphous phase of ferrihydrite for the present study has been confirmed by X-ray diffraction (XRD) and Mössbauer spectroscopy at room temperature and low temperatures (40 K and 20 K). Hematite nanoparticles with crystallite size about 8, 38 and 70 nm were obtained after annealing the as-prepared samples at 400, 600 and 800 degrees C respectively in air atmosphere. Superparamagnetism has been found in 8 nm sized hematite nanoparticles which has been confirmed from the magnetic hysteresis loop with zero remanent magnetization and coercive field and also from the superparamagnetic doublet of its room temperature Mössbauer spectrum. The magnetic properties of the 38 and 70 nm sized particles have been studied by room temperature magnetic hysteresis loop measurements and Mössbauer spectroscopy. The coercive field in these hematite nanoparticles increases with increasing particle size. Small amount of spinel MgFe2O4 phase has been detected in the 800 degrees C annealed sample.

Multiferroic nano-composite (1-x) BiFeO3–x Li0.5Fe2.5O4 (x=0.25 and 0.5) have been successfully synthesized by mixing the two phases, prepared independently by two different methods followed by annealing at 600 0 C. Existence of the two phases in the composite is confirmed by x-ray diffraction pattern. Average particle size is calculated to be about 45 nm for both of these phases. The saturation magnetization, remnant magnetization and coercive field increases linearly with increasing ferromagnetic phase (Li0.5Fe2.5O4) as investigated by VSM measurement. Local magnetic behaviors have been investigated by 57 Fe Mossbauer spectroscopic studies. Large dielectric constant of the order of 10 3 -10 4 has been observed in these composites. Copyright © 2013 VBRI press

Single phase BiFeO3 nanoparticles have been successfully synthesized for the first time by a novel citrate combustion method without using any solvent. Well mixed metal nitrates along with citric acid which is used as fuel combust to give BiFeO3 nanoparticles after annealing. These particles are single phase in nature and crystallize in the rhombohedral distorted perovskite structure (space group-R3c) which has been confirmed by the Rietveld refinement of the room temperature powder x-ray diffraction data. Nearly spherical particles of average particle size 47 nm have been seen from transmission electron micrograph. Room temperature magnetic hysteresis measurement shows weak ferromagnetism though the magnetization does not saturate upto 1.75 T applied field. The coercive field value is calculated to be 180 Oe which is 3 times higher than that prepared by solvent free combustion method using glycine. 57 Fe Mossbauer spectrum can be fitted with a sextet corresponding to single magnetic state of hyperfine field about 49.5 T corresponding to Fe 3+ state of the iron atom. The dielectric relaxation and ac conductivity as a function of frequency have been discussed. High dielectric permittivity has not been found in these nanoparticles like other reported BiFeO3 ceramics. Copyright © 2012 VBRI press.

The ZnO:Fe nanoparticles of mean size 3–10 nm were synthesized at room temperature by simple co-precipitation method. The crystallite structure, morphology and size estimation were performed by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM). The wurtzite structure of ZnO gradually degrades with the increasing Fe doping concentration. The magnetic behavior of the nanoparticles of ZnO with varying Fe doping concentration was investigated using a vibrating sample magnetometer (VSM). Initially these nanoparticles showed strong ferromagnetic behavior, however at higher doping percentage of Fe, the ferromagnetic behavior was suppressed and paramagnetic nature was observed. The enhanced antiferromagnetic interaction between neighboring Fe–Fe ions suppressed the ferromagnetism at higher doping concentrations of Fe. Room-temperature Mossbauer spectroscopy investigation showed Fe 3+ nature of the iron atom in ZnO matrix.

The pure and Fe-doped CuO nanoparticles of the series Cu(1-x)Fe(x)O (x = 0.00, 0.02, 0.04, 0.06 and 0.08) were successfully prepared by a simple low temperature sol-gel method using metal nitrates and citric acid. Rietveld refinement of the X-ray diffraction data showed that all the samples were single phase crystallized in monoclinic structure of space group C2/c with average crystallite size of about 25 nm and unit cell volume decreases with increasing iron doping concentration. TEM micrograph showed nearly spherical shaped agglomerated particles of 4% Fe-doped CuO with average diameter 26 nm. Pure CuO showed weak ferromagnetic behavior at room temperature with coercive field of 67 Oe. The ferromagnetic properties were greatly enhanced with Fe-doping in the CuO matrix. All the doped samples showed ferromagnetism at room temperature with a noticeable coercive field. Saturation magnetization increases with increasing Fe-doping, becomes highest for 4% doping then decreases for further doping which confirms that the ferromagnetism in these nanoparticles are intrinsic and are not resulting from any impurity phases. The ZFC and FC branches of the temperature dependent magnetization (measured in the range of 10-350 K by SQUID magnetometer) look like typical ferromagnetic nanoparticles and indicates that the ferromagnetic Curie temperature is above 350 K.

Maghemite (&#947-Fe 2 O 3 ) nanoparticles are synthesized by chemical co-precipitation technique in AOT-microemulsion with a view to have possible application for biotagging. The investigations by means of X-ray diffraction, isothermal magnetization M (H) and 57 Fe Mossbauer Spectroscopy show that the particles are nonspherical, mostly of rod shape. The inter-particle interaction is so large that even a powder sample of thickness about 40 mg/cm 2 shows preferential orientation of magnetic moments in the plane of the sample. The saturation magnetization is much lower than the expected values for maghemite. Keywords : Maghemite, Magnetic nanoparticles, Magnetic Ordering, Mossbauer spectroscopy International Journal of Engineering, Science and Technology , Vol. 2, No. 8, 2010, pp. 33-39

A set of Ni 0.5 Zn 0.5 Fe 2 O 4 samples were prepared by citrate precursor route to investigate the growth mechanism and its effect on cationic distribution. Following the information from DTA–TGA analysis, samples were annealed at 550 &#176C, 700 &#176C and 750 &#176C. Magnetization and Mossbauer studies suggest that initially the cationic distribution deviates from its normal preferences but it gets back to the normal preference at a temperature around 675 &#176C. It has been found that size onset for having the bulk cation configuration exclusively depends on the composition. Keywords : Mossbauer Spectroscopy; Ferrite; Nanoparticles, Cationic distribution International Journal of Engineering, Science and Technology , Vol. 2, No. 8, 2010, pp. 104-109

10% Co‐doped BiFeO3 nanoparticles have been prepared by a low temperature sol‐gel method. XRD result shows that particles are single phase in nature and crystallizes in distorted perovskite structure (space group R3c) with average particle size of 60 nm. Room temperature ferromagnetism along with saturation magnetization of about 2.24 emu/g and high coercive field of 1260 Oe has been found by VSM measurements. Mossbauer data can be fitted with single magnetic sextet of isomer shift about 0.35 mm/s and hyperfine field about 49 T indicating Fe3+ nature of Fe atom present in Co‐doped BiFeO3 nanoparticles.

Polycrystalline samples of ternary rare earth germanides R$_{2}$Co$_{3}$Ge$_{5}$(R = La, Ce and Pr) have been prepared and investigated by means of magnetic susceptibility, isothermal magnetization, electrical resistivity and specific heat measurements. All these compounds crystallize in orthorhombic U$_{2}$Co$_{3}$Si$_{5}$ structure (space group \textit{Ibam}). No evidence of magnetic or superconducting transition is observed in any of these compounds down to 2 K. The unit cell volume of Ce$_{2}$Co$_{3}$Ge$_{5}$ deviates from the expected lanthanide contraction, indicating non trivalent state of Ce ions in this compound. The reduced value of effective moment ($\mu_{eff}$ $\approx$ 0.95 $\mu_{B}$) compared to that expected for trivalent Ce ions further supports valence fluctuating nature of Ce in Ce$_{2}$Co$_{3}$Ge$_{5}$. The observed temperature dependence of magnetic susceptibility is consistent with ionic interconfiguration fluctuation (ICF) model. Although no sharp anomaly due to a phase transition is seen, a broad Schottky-type anomaly is observed in the magnetic part of specific heat of Pr$_{2}$Co$_{3}$Ge$_{5}$. An analysis of $C_{mag}$ data suggests a singlet ground state in Pr$_{2}$Co$_{3}$Ge$_{5}$ separated from the singlet first excited state by 22 K and a doublet second excited state at 73 K., Comment: 12 pages, 5 figures

In the present study, monodispersed CeO2 nanoparticles (NPs) of size 8.5 ± 1.0, 11.4 ± 1.0 and 15.4 ± 1.0 nm were synthesized using the sol-gel method. Size-dependent structural, optical and magnetic properties of as-prepared samples were investigated by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), high resolution transmission electron microscopy (HR-TEM), ultra-violet visible (UV-VIS) spectroscopy, Raman spectroscopy and vibrating sample magnetometer (VSM) measurements. The value of optical band gap is calculated for each particle size. The decrease in the value of optical band gap with increase of particle size may be attributed to the quantum confinement, which causes to produce localized states created by the oxygen vacancies due to the conversion of Ce4+ into Ce3+ at higher calcination temperature. The Raman spectra showed a peak at ∼461 cm-1 for the particle size 8.5 nm, which is attributed to the 1LO phonon mode. The shift in the Raman peak could be due to lattice strain developed due to variation in particle size. Weak ferromagnetism at room temperature is observed for each particle size. The values of saturation magnetization (Ms), coercivity (Hc) and retentivity (Mr) are increased with increase of particle size. The increase of Ms and Mr for larger particle size may be explained by increase of density of oxygen vacancies at higher calcination temperature. The latter causes high concentrations of Ce3+ ions activate more coupling between the individual magnetic moments of the Ce ions, leading to an increase of Ms value with the particle size. Moreover, the oxygen vacancies may also produce magnetic moment by polarizing spins of f electrons of cerium (Ce) ions located around oxygen vacancies, which causes ferromagnetism in pure CeO2 samples.

Iron/iron-oxide nano particles are synthesized using electrodeposition technique. The particles are well crystalline bcc iron with disordered oxides of iron on the surface. The particles show very small coercivity displaying superparamagnetic behavior of the iron core in magnetization measurement using Vibrating Sample Magnetometer. But the same particles show no trace of supermagnetism or fluctuation of magnetic moments in Mössbauer measurements, showing the role of time scales of measuring equipment in fine particle magnetism. Keywords: Iron/iron oxide composite, Magnetic nanoparticles, VSM, Mössbauer spectroscopy International Journal of Engineering, Science and Technology, Vol. 2, No. 8, 2010, pp. 66-72