Room temperature ferromagnetism in Fe-doped CuO nanoparticles.

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.

Mössbauer and magnetic studies of surfactant mediated Ca-Mg doped ferrihydrite nanoparticles.

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.

Electron- and ion-beam-induced maneuvering of nanostructures: phenomenon and applications.

Electron-and ion-induced bending (EIB/IIB) phenomena have been studied in self-supported polycrystalline metallic and metal-amorphous bilayered nanocantilevers. The experiments reveal many interesting facts regarding electron/ion-matter interaction, which builds a proper foundation for the understanding of the phenomenon. The mechanism for bending of metallic cantilevers has been proposed to be primarily due to void-induced stress generation during ion beam irradiation. On the other hand, thermal effects have been found to play the dominant role in the case of bending of bilayer (amorphous-metal) nanocantilevers. The instantaneous, reversible, highly controllable and permanent nature of the process has been exploited to fabricate several complicated nanostructures in three dimensions. IIB of the fabricated cantilevers is shown to have a high precession mass sensing aptitude, capable of detecting a change in mass of the order of femtograms.

Magnetic studies of multiferroic Bi(1-x)Sm(x)FeO(3) ceramics synthesized by mechanical activation assisted processes.

Bi(1-x)Sm(x)FeO(3) (x = 0.0-0.2) ceramic samples were prepared by mechanical activation assisted solid-state-reaction synthesis. A stoichiometric mixture of Bi(2)O(3), Sm(2)O(3), and Fe(2)O(3) powders was mechanically milled and this was followed by heat treatment at 700 °C for 1 h. Room temperature x-ray diffraction patterns confirmed the formation of perovskite structured Bi(1-x)Sm(x)FeO(3) phase. Vibrating sample magnetometry measurements showed that to a certain extent, Sm doping of BiFeO(3) leads to increased magnetization and a sharp magnetic transition at ∼380 °C. Mössbauer spectroscopy confirmed the presence of single-phase material for the doped compositions whereas electron paramagnetic resonance analysis showed the effect of doping on the variation in the degree of canting in the samples. At doping levels of 10 at.% Sm, the improvement in the magnetic behaviour appears to arise from a combination of the propensity of the samples to form pure phase material, partial destruction of spin cycloids, increased canting of spins and interaction between magnetic ions.

Properties of nanocrystalline Fe75Si15M10 (M-Cr and Al) powders prepared by mechanical alloying.

We report the structural and magnetic properties of the nanocrystalline Fe75Si15M10 (M-Al and Cr) powders prepared by mechanical alloying. The milling process produced a non-equilibrium solid solutions of bcc alpha-Fe(Si,Cr) and alpha-Fe(Si,Al). The average dislocation density increases and the average crystallite size decreases with increasing milling time. Magnetic property studies show that the coercivity of the sample increases and magnetization of the sample decreases with increasing milling time. The evolution of a non-equilibrium solid solution and the resulting magnetic properties of nanocrystalline powders are explained on the basis of Neel theory and modified random anisotropy model proposed by Shen et al.

Anomalous structural and magnetic behaviour of Fe-25 at.% Ni alloy due to mechanical strain.

Mechanical strain was induced in Fe-25 at.% Ni alloy by filing the ingots into powder form. The phase transformations induced by the deformation thus caused and subsequent annealing were studied by x-ray diffraction, magnetization measurement and Mössbauer spectroscopy. It is concluded that around one-third of the Fe atoms became segregated from the Fe-Ni alloy due to filing. Annealing of the filed powder led to recombination of this segregated Fe to form an apparently body-centred cubic (bcc) phase of Fe-Ni which shows little magnetic ordering at room temperature in magnetization measurements or in Mössbauer spectroscopy. The single-line Mössbauer spectrum of this phase splits into a six-line pattern below 100 K.

Structural and Magnetic Properties of Dilute Ca²âº Doped Iron Oxide Nanoparticles.

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. Mössbauer spectra for all the nanoparticles could be fitted with a sextet corresponding to the single magnetic state of the iron atoms in its Fe³âº 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 Ca²âº 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.

Fluoride adsorption studies on mixed-phase nano iron oxides prepared by surfactant mediation-precipitation technique.

Mixed nano iron oxides powder containing goethite (α-FeOOH), hematite (α-Fe(2)O(3)) and ferrihydrite (Fe(5)HO(8)·4H(2)O) was synthesized through surfactant mediation-precipitation route using cetyltrimethyl ammonium bromide (CTAB). The X-ray diffraction, FTIR, TEM, Mössbauer spectroscopy were employed to characterize the sample. These studies confirmed the nano powder contained 77% goethite, 9% hematite and 14% ferrihydrite. Fluoride adsorption onto the synthesized sample was investigated using batch adsorption method. The experimental parameters chosen for adsorption studies were: pH (3.0-10.0), temperature (35-55°C), concentrations of adsorbent (0.5-3.0 g/L), adsorbate (10-100 mg/L) and some anions. Adsorption of fluoride onto mixed iron oxide was initially very fast followed by a slow adsorption phase. By varying the initial pH in the range of 3.0-10.0, maximum adsorption was observed at a pH of 5.75. Presence of either SO(4)(2-) or Cl(-) adversely affected the adsorption of fluoride in the order of SO(4)(2-)>Cl(-). The FTIR studies of fluoride loaded adsorbent showed that partly the adsorption on the surface took place at surface hydroxyl sites. Mössbauer studies indicated that the overall absorption had gone down after fluoride adsorption that implies it has reduced the crystalline bond strength. The relative absorption area of ferrihydrite was marginally increased from 14 to 17%.

Nuclearity control in molecular iron phosphates through choice of iron precursors and ancillary ligands.

The potential of a mono-organophosphate ester in assembling low to medium nuclearity iron complexes with novel topological architectures has been investigated. Reaction of 2,6-diisopropylphenyl dihydrogen phosphate (dipp-H(2)) with ferrous acetate under an inert atmosphere resulted in the formation of mononuclear, [Fe(II)(dipp-H)(2)(py)(4)] (1) (py = pyridine), dinuclear [Fe(III) (2)O(dipp-H)(4)(3,5-dmpz)(3)(thf)](3,5-dmpz)(thf)(3) (2) (3,5-dmpz = 3,5-dimethylpyrazole, thf = tetrahydrofuran), and trinuclear [Fe(III) (2)Fe(II)O(dipp-H)(6)(thf)(3)](collidine) (3) complexes by changing the ancillary amine used in the reaction. Use of a preformed mu(3)-oxo bridged trinuclear complex, [Fe(III) (3)O(O(2)CR)(6)(H(2)O)(3)]X (X = Cl and NO(3)), as the precursor yielded two tetranuclear iron phosphates, [Fe(III) (4)O(dipp)(3)(py)(4)(PhCOO)(4)](toluene)(3) (4) and [Fe(III) (4)O(dipp)(3)(OAc)(4)(py)(4)](py)(2) (5), having a core structure similar to those found in tetranuclear iron phosphonates. When FeCl(3)6H(2)O was used as the iron precursor, an unprecedented pentanuclear iron phosphate complex, [Fe(III) (5)O(dipp)(6)(py)(4)Cl(2)][pyH] (6) with a novel structure was isolated. Another pentanuclear complex having a similar core structure, [Fe(5)O(dipp)(6)(HO(2)CPh)(3)(CH(3)CN)(3)Cl] (7) was isolated on treatment of dipp-H(2) with the triangular complex, [Fe(III) (3)O(O(2)CPh)(6)(H(2)O)(3)]Cl in the absence of any added amine co-ligand. Compounds 1-7 have been characterized by analytical techniques, spectroscopic studies, single crystal X-ray diffraction studies, and magnetic measurements. The Mössbauer studies carried out at room temperature support the formulation of all the compounds.

Chloroform- and water-soluble sol-gel derived Eu+++/Y2O3 (red) and Tb+++/Y2O3 (green) nanophosphors: synthesis, characterization, and surface modification.

Eu+++ and Tb+++ ions have been incorporated into nanodimensional yttrium oxide host matrices via a sol-gel process using Y5O(OPr(i))13 as precursor (OPr(i) = isopropoxy). The as-synthesized white powders have been annealed at different temperatures. Photoluminescence (PL) spectroscopy and X-ray diffraction (XRD) have been used as tools for documenting the characteristics of these powders. For Eu+++-doped powders, a comparison of the Eu+++, 5D0-->7F1, and 5D0-->7F2 peak intensities in the emission spectra reveals that the dopant ions are occupying unsymmetrical sites in the host yttrium oxide in all the samples. For Tb+++-doped powders, the characteristic terbium 5D3-->7Fn and 5D-->7Fn (n = 2-6) transitions were visible only in the samples that had been annealed above 500 degrees C. Samples of the doped particle powders were suspended in chloroform by fragmenting the powder with and without sonification under the presence of trioctylphosphine oxide, or a mixture of oleic acid and dioctyl ether. The resulting clear colorless (for Eu+++) and light green translucent (for Tb+++) solutions of the suspended particles showed red and green luminescence upon UV excitation, respectively. In addition, suspension in water has been achieved by fragmenting the powder in the presence of dichloroacetic acid. Transmission electron micrograph investigation of the soluble particles shows single dispersed particles along with agglomerates. The changes in the luminescence due to fragmentation of the particle powder and due the influence of the surfactant of the suspended colloidal particles are discussed.