G. Chandrasekaran

Impact of Gd3+ substitution on the structural, magnetic and electrical properties of cobalt ferrite nanoparticles

In this work, we have focused on the influence of Gd3+ substitution on the structural, magnetic and electrical properties of cobalt ferrite synthesized using a sol–gel auto-combustion method. The powder X-ray diffraction analysis reveals that the Gd-substituted cobalt ferrites crystallize in a single phase spinel structure for lower concentrations of Gd3+, while a trace of GdFeO3 appears as a minor phase for higher concentrations. Raman and Fourier transform infrared spectra confirm the formation of the spinel structure. Furthermore, Raman analysis shows that the inversion degree of cobalt ferrite decreases with Gd3+ doping. The field emission scanning electron microscopy images show that the substitution of small amounts of Gd3+ causes a considerable reduction of the grain size. Studies on the magnetic properties reveal that the coercivity of Gd-substituted cobalt ferrites enhances from 1265 Oe to 1635 Oe, the saturation magnetization decreases monotonically from 80 emu g−1 to 53.8 emu g−1 and the magnetocrystalline anisotropy constant increases from 5.8 × 105 erg cm−3 to 2.23 × 106 erg cm−3 at 300 K. The electrical properties show that the Gd3+ doped samples exhibit high dielectric constant (616 at 100 Hz) and ac conductivity (4.83 × 10−5 S cm−1 at 100 Hz) values at room temperature. The activation energy is found to decrease from 0.408 to 0.347 eV with the rise in Gd3+ content. The impedance study brings out the effect of the bulk grain and the grain boundary on the electrical resistance and capacitance of cobalt ferrite. Gd substitution and the nano-size of cobalt ferrite enhance the electrical and magnetic properties which could enable a higher memory storage capability.

Electrical and FTIR studies on Al substituted Mn–Zn mixed ferrites

Mixed ferrites of manganese and zinc with the substitution of aluminum are prepared by the ceramic double-sintering method. Confirmation of single-phase and polycrystalline ferrites is made from X-ray diffraction patterns and experimental and theoretical values of lattice constant are compared. Distribution of cations on A and B sites is concluded. A.c. conductivity and FTIR characterizations are done and the logarithm of conductivity (log σ) dielectric constant (ε) and tan δ at various frequencies (ω) and temperatures (T) are reported. Hopping of electrons between localized d bands of ions is the interesting feature of these ferrites and the mechanism of hopping is discussed. Activation energy and vibration frequencies are discussed as a function of aluminum concentration.

PHASE EVOLUTION IN BiFeO3 NANOPARTICLES PREPARED BY GLYCINE-ASSISTED COMBUSTION METHOD

We report here the evolution of phase purity in BiFeO3 (BFO) nanoparticles prepared by a novel glycine-assisted combustion method. The study of phase evolution with temperature, in nanoparticles of BFO is carried out using X-ray diffraction (XRD) and thermogravimetry (TG) coupled with differential scanning calorimetry (DSC). Optimum annealing conditions for the synthesis of single-phase BiFeO3 nanoparticles are obtained. The morphology and average grain size of the nanoparticles are determined using a scanning electron microscope (SEM) and an atomic force microscope (AFM), respectively. In situ microanalysis revealed that there are no significant deviations in the stoichiometry of the prepared compound. The magnetic behavior of BFO nanoparticles at 300 K has been studied using a vibrating sample magnetometer (VSM). A weak hysteresis loop observed is suggestive of the presence of partially destructed antiferromagnetic arrangement of moments in the material. Low temperature magnetization measurements reveal the presence of spin glass–like transition in the nanoparticles of BFO. A well-developed ferroelectric hysteresis loop has been observed at room temperature at a maximum applied field of 45 kV/cm. The nanoparticles of BFO in the present study are found to possess both magnetic and ferroelectric order at room temperature.

Structural, optical and electron paramagnetic resonance studies on Cu-doped ZnO nanoparticles synthesized using a novel auto-combustion method

Nanocrystalline Zn1 − xCuxO (x = 0, 0.02, 0.04, 0.06, 0.08) samples were synthesized by a novel auto-combustion method using glycine as the fuel material. The structural, optical and magnetic properties of the samples were characterized using XRD, SEM, photoluminescence (PL) and electron paramagnetic resonance (EPR) spectroscopies. The XRD spectra of samples reveal the hexagonal wurtzite structures of ZnO. As the copper content increases, a diffraction peak at 2θ = 39° corresponding to secondary phase of CuO ([111] crystalline face) appears when x ⩽ 6 mol.%. PL spectra of the samples show a strong ultraviolet (UV) emission and defect related visible emissions. Cu-doping in ZnO can effectively adjust the energy level in ZnO, which leads to red shift in the emission peak position in UV region. The EPR spectra of Cu-doped ZnO nanoparticles show a distinct and broad signal at room temperature, suggesting that it may be attributed to the exchange interactions within Cu2+ ions.

Impact of Fe on structural modification and room temperature magnetic ordering in BaTiO3.

Ba1-xFexTiO3 (x=0, 0.005, 0.01) polycrystalline ceramics are prepared using solid state reaction method. Structural studies through XRD, Raman and XPS confirm single tetragonal phase for BaTiO3 whereas a structural disorder tends to intervene with the introduction of smaller Fe ions which reduces the tolerance factor and tetragonality ratio. Grain size of the samples is estimated using SEM micrographs with ImageJ software and chemical composition is confirmed using EDX spectra. Raman spectra measured in the temperature range of 303K to 573K showers light on the structural phase transition exploiting a significant disappearance of the 306cm-1 mode. Further, structural analyses suggest the entry of Fe into the B-site upon increasing its concentration in BaTiO3. The dopant sensitive modes lying at around 640cm-1 and 650cm-1 are assigned to lattice strain. A reduction in ferroelectric to paraelectric transition temperature is observed with a transformation from diffused type to normal ferroelectric upon the increased Fe content. The oxidation state of Fe in the BaTiO3 lattice has been decided using EPR Spectra precisely. Room temperature magnetic ordering is observed in Fe substituted BaTiO3 using PPMS. The coexistence of ferroelectric and magnetic ordering is established in the present study for optimized Fe substituted BaTiO3.

Optical, electrical and ferromagnetic studies of ZnO:Fe diluted magnetic semiconductor nanoparticles for spintronic applications

In the present investigation, diluted magnetic semiconductor (Zn1-xFexO) nanoparticles with different doping concentrations (x=0, 0.02, 0.04, 0.06, and 0.08) were successfully synthesized by sol-gel auto-combustion method. The crystal structure, morphology, optical, electrical and magnetic properties of the prepared samples were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive analysis using x-rays (EDAX), ultraviolet-visible spectrophotometer, fluorescence spectroscope (FS), vibrating sample magnetometer (VSM) and broad band dielectric spectrometer (BDS). XRD results reveal that all the samples possess hexagonal wurtzite crystal structure with good crystalline quality. The absence of impurity phases divulge that Fe ions are well incorporated into the ZnO crystal lattice. The substitutional incorporation of Fe3+ at Zn sites is reflected in optical absorption spectra of the samples. Flouorescence spectra of the samples show a strong near-band edge related UV emission as well as defect related visible emissions. The semiconducting behavior of the samples has been confirmed through electrical conductivity measurements. Magnetic measurements indicated that all the samples possess ferromagnetism at room temperature.

Structural and Magnetic properties of Barium Hexaferrrite Prepared through Sol-Gel Auto combustion technique

Barium Hexaferrite nano particles were prepared through glycine assisted sol-gel auto combustion method with a minimal GNR (glycine to nitrate ratio) and the pH values of 4, 6 and 9. The present work aimed at the study on the effect of pH on the synthesis, structural and magnetic properties of barium hexaferrite samples. X-Ray Diffraction patterns reveal the formation of hexagonal magneto-plumbite structure of BaFe12O19 with a weak intensity of secondary phase in the case of pH 4 and pH 6 samples. Interestingly disappearance of secondary phase at pH 9 sample was noticeable feature. SEM micrographs of the samples show the formation of characteristic hexagonal shape of Barium hexaferrite. Constituent elements and chemical composition were analyzed using EDX spectrum. FTIR spectra show the different metal-oxygen stretching vibration modes at 440, 546 and 596-640 cm−1 which confirms the formation of BaFe12O19. In addition pH 4 and pH 6 samples show a weak band at 770 cm−1 revealing the formation of secondary ...

Dielectric properties of Mn0.5Zn0.5Fe2O4 ferrite nanoparticles

Mn0.5Zn0.5Fe2O4 ferrite nanoparticles have been prepared by sol-gel auto-combustion method with a view to understand the role of oxidizer to fuel ratio (OFR) on the dielectric properties. XRD study shows the formation of cubic ferrite with spinel structure and particle size increases with the increase in concentration of fuel. Dielectric properties and AC conductivity of the sample measured at room temperature are reported. OFR plays a vital role in determining the dielectric properties and AC conductivity of the prepared samples.

Effect of Annealing Temperature on Titania Nanoparticles

Titania polycrystalline samples are prepared by using sol-gel route hydrolyzing a alkoxide titanium precursor under acidic conditions. The as prepared samples are treated with different calcination temperatures. The anatase phase of titania forms when treated below 600°C, above that temperature the anatase phase tends to transform into the rutile phase of titania. The experimental determination of average grain size, phase formation, lattice parameters and the crystal structures of titania samples at different calcinations is done using X-ray diffraction (XRD). Fourier Transform Infra-red Spectroscopy (FTIR), UV-vis-NIR spectroscopy and Scanning Electron Microscopy (SEM) and Energy Dispersive Analysis X-ray are used to characterize the samples to bring impact on the respective properties.

Correction to: Structural, morphological and magnetic characters of PVP coated ZnFe 2 O 4 nanoparticles

The original version of this article (https://doi.org/10.1007/s10854-017-8127-4) was published with following errors