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The gadolinium (Gd3+) substituted zinc ferrite nanoparticles (ZnFe2−xGdxO4) for Gd3+ (x = 0.00, 0.05, 0.10, 0.20) have been synthesized by honey mediated sol-gel auto-combustion method. The X-ray diffraction study revealed the formation of spinel ferrite crystal structure. The Raman spectroscopy and Fourier transform infrared spectroscopy study well support the XRD results analysis. The field emission scanning electron microscopy micrograph revealed spherical morphology and grain size around 10-30 nm for ZnFe2−xGdxO4 (x = 0.10) nanoparticles. The presence of Zn2+ and Fe3+ oxidation state in synthesized nanoparticles was confirmed by X-ray photoelectron spectroscopy. Magnetic properties of the Gd3+ substituted zinc ferrite nanoparticles were investigated by vibrating sample magnetometer at room temperature. The conversion of magnetic hysteresis curves from ferromagnetic to a paramagnetic with the substitution of Gd3+ in zinc ferrite nanoparticles was observed. Frequency dependent dielectric constant and ac conductivity measurements revealed that Gd3+ substitution improved the value of dielectric constant and ac conductivity of the Gd3+ substituted zinc ferrite nanoparticles. Further, the existence of two semicircles in Cole-Cole plot demonstrated the role of both grains and grain boundaries to conduction process in synthesized Gd3+ ion substituted zinc ferrite nanoparticles. Furthermore, the grain relaxation time (τg), grain boundary relaxation time (τgb), grain resistance (Rg), grain capacitance (Cg), grain boundary resistance (Rgb) and grain boundary capacitance (Cgb) for synthesized ZnFe2−xGdxO4 (x = 0.00, 0.05, 0.10, 0.20) nanoparticles have been calculated using modulus spectroscopy analysis. [ABSTRACT FROM AUTHOR]

In this work, we have studied the influence of La substitution on structural, magnetic, dielectric, electrical and modulus spectroscopic characteristics of cobalt ferrite nanoparticles synthesized by starch-assisted sol-gel combustion method. The powder X-ray diffraction analysis confirms the formation of single-phase CoFeLaO (x = 0.00, 0.05, 0.10, 0.15, 0.20) spinel ferrite nanoparticles. Raman spectroscopy study also reveals the formation of single phase spinel ferrite crystal structure. The morphological feature of synthesized ferrite nanoparticle was observed by scanning electron microscopy that demonstrate formation of spherical nanoparticles with grain size 10-50 nm. The presence of constituent's, i.e., Co, Fe and La were authenticated by energy dispersive X-ray analysis. The magnetic parameters are measured by employing vibrating sample magnetometer. The saturation magnetization decreases with La substitution, whereas coercivity shows anomalous behaviour. Cation redistribution in spinel ferrite nanoparticles are confirmed by X-ray photoelectron spectroscopy. The variation of dielectric constant (ϵ′, ϵʺ), loss tangent (tanδ), ac conductivity (σ), electric modulus (M′, Mʺ) and impedance (Z′, Zʺ) as a function of La ion concentration and frequency has been investigated. The dielectric constant and ac conductivity increases with increase of La substitution, whereas dielectric loss tangent exhibits anomalous behaviour. The modulus spectra reveal two semicircles associated with grain and grain boundary effects. The cole-cole plots in modulus formalism show that the electrical characteristics contribute from both the grains and grain boundaries. Modulus spectra suggest that the distribution of relaxation times and conduction mechanism are influenced by La ion substitution in cobalt ferrite nanoparticles. [ABSTRACT FROM AUTHOR]

Zinc ferrite nanoparticles have been synthesized by sol-gel auto-combustion method using starch as a fuel. The impact of annealing temperature on crystal structure, microstructure and dielectric properties is investigated. The powder X-ray diffraction results demonstrated the formation of well crystalline single cubic phase of zinc ferrite at annealing temperature 400 °C. Increase in crystallinity, crystallite size and lattice parameter were observed with increase of annealing temperature 600 and 800 °C. Field Emission Scanning Electron Microscopy study revealed that the zinc ferrite nanoparticles annealed at 400 °C were spherical with a particle size range 5-30 nm. These particles annealed at 600 °C were also spherical in morphology with a particle size range 10-50 nm. However, zinc ferrite nanoparticles annealed at 800 °C were polyhedron in morphology with particle size range 15-70 nm. The variations of real and imaginary part of dielectric constant, tan δ and AC conductivity are studied at room temperature. The dielectric spectral analysis demonstrated that the dielectric constant is higher at low frequency and decreases with increase in frequency. This dielectric behavior follows the Maxwell-Wagner interfacial polarization. The dielectric constant and dielectric loss tangent of zinc ferrite nanoparticles exhibit dependence on annealing temperature. The impact of annealing temperature is also analyzed through Modulus spectroscopy and Impedance analysis to understand the interaction between grain and grain boundary in zinc ferrite nanoparticles. [ABSTRACT FROM AUTHOR]

The iron oxide nanoparticles have been synthesized by coprecipitation and solvothermal reduction methods. The particles obtained differ in size, the mean size of particles coprecipitated is of 13 nm and the particles, prepared by solvothermal reduction method have a size of 20 nm. Both kinds of nanoparticles demonstrate narrow particles sizes distribution. The particles which are prepared by coprecipitation method have narrow particles sizes distribution with mean size diameter of 13 nm and the particles, prepared by solvothermal reduction method have a size of 20 nm. The X-ray diffraction data analysis revealed that highly crystalline and single-phase magnetite nanoparticles are formed by solvothermal reduction technique, whereas coprecipitation leads to the formation of multi-phase composition of a magnetite (72%) and maghemite (28%). According to the size of nanoparticles obtained, they are in superparamagnetic state for iron oxides. The saturation magnetization of solvothermal prepared particles is higher than those for coprecipitated due to their higher crystallinity and phase purity. Nevertheless, the glycerol dispersion of particles coprecipitated shows higher SLP values than the dispersion of the particles, synthesized by solvothermal reduction method. The heating efficiency of nanoparticles based dispersions is explained by the particles size effect and properties of carrier medium. [ABSTRACT FROM AUTHOR]

In this work, a facile and green method for gadolinium doped cobalt ferrite (CoFe 2−x Gd x O 4 ; x = 0.00, 0.05, 0.10, 0.15, 0.20) nanoparticles by using ultrasonic irradiation was reported. The impact of Gd 3+ substitution on the structural, magnetic, dielectric and electrical properties of cobalt ferrite nanoparticles was evaluated. The sonochemically synthesized spinel ferrite nanoparticles were characterized by X-ray Diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), vibrating sample magnetometer (VSM). X-ray diffraction (XRD) study confirmed the formation of single phase spinel ferrite of CoFe 2−x Gd x O 4 nanoparticles. XRD results also revealed that ultrasonic irradiation seems to be favourable to achieve highly crystalline single crystal phase gadolinium doped cobalt ferrite nanoparticles without any post annealing process. Fourier Transform Infrared and Raman Spectra confirmed the formation of spinel ferrite crystal structure. X-ray photoelectron spectroscopy revealed the impact of Gd 3+ substitution in CoFe 2 O 4 nanoparticles on cation distribution at the tetrahedral and octahedral site in spinel ferrite crystal system. The electrical properties showed that the Gd 3+ doped cobalt ferrite (CoFe 2−x Gd x O 4 ; x = 0.20) exhibit enhanced dielectric constant (277 at 100 Hz) and ac conductivity (20.2 × 10 −9 S/cm at 100 Hz). The modulus spectroscopy demonstrated the impact of Gd 3+ substitution in cobalt ferrite nanoparticles on grain boundary relaxation time, capacitance and resistance. Magnetic property measurement revealed that the coercivity decreases with Gd 3+ substitution from 234.32 Oe (x = 0.00) to 12.60 Oe (x = 0.05) and further increases from 12.60 Oe (x = 0.05) to 68.62 Oe (x = 0.20). Moreover, saturation magnetization decreases with Gd 3+ substitution from 40.19 emu/g (x = 0.00) to 21.58 emu/g (x = 0.20). This work demonstrates that the grain size and cation distribution in Gd 3+ doped cobalt ferrite nanoparticles synthesized by sonochemical method, is effective in controlling the structural, magnetic, and electrical properties, and can be find very promising applications. [ABSTRACT FROM AUTHOR]

This paper reports a honey-mediated green synthesis of ZnFe 2 O 4 spinel ferrite nanoparticles and the effect of further annealing on structural, magnetic, optical, dielectric and electrical properties. X-ray diffraction study confirmed the well formation of ZnFe 2 O 4 spinel ferrite crystal structure. Raman and Fourier transform infrared spectroscopy confirmed the formation of spinel ferrite crystal structure. The scanning electron microscopy study revealed the formation of spherical morphology at lower annealing temperature with achieved particle size 30–60 nm, whereas, octahedral like morphology at higher annealing temperature with particle size 50–400 nm. Magnetization measurements were carried out using a vibrating sample magnetometer at room temperature. The estimated magnetic parameter such as saturation magnetization (M s ), remanence (M r ) and coercivity (H c ) showed variation in value with nano-crystallite size. The highest saturation magnetization (M s ) was 12.81 emu/g for as-synthesized ZnFe 2 O 4 spinel ferrite nanoparticles, whereas, highest coercivity (H c ) was 25.77 Oe for ZnFe 2 O 4 nanoparticles annealed at high temperature 1000 °C. UV–Visible reflectance spectroscopy showed the band gap variation from 1.90 eV to 2.14 eV with the increase of annealing temperature. The dielectric constant and dielectric loss were decreased with frequency showing the normal behavior of spinel ferrites. The variation in conductivity is explained in terms of the variation in microstructure and variation in the mobility of charge carriers associated with the cation redistribution induced by annealing or grain size. The modulus and impedance spectroscopy study revealed the influence of bulk grain and the grain boundary on the electrical resistance and capacitance of ZnFe 2 O 4 nanoparticles. The results presented in this work are helpful for green synthesis of well-controlled size, morphology and physical properties of ZnFe 2 O 4 nanoparticles. [ABSTRACT FROM AUTHOR]

• Sonochemical Synthesis of MnFe 2 O 4 single-phase spinel ferrite structure. • Impact of sonochemical time and percentage amplitude of ultrasonic power input. • Cation redistribution with increase of sonication time. • Physical characteristics controlled by sonication synthesis condition for specific application. Herein, we report sonochemical synthesis of MnFe 2 O 4 spinel ferrite nanoparticles using UZ SONOPULS HD 2070 Ultrasonic homogenizer (frequency: 20 kHz and power: 70 W). The sonication time and percentage amplitude of ultrasonic power input cause appreciable changes in the structural, cation distribution and physical properties of MnFe 2 O 4 nanoparticles. The average crystallite size of synthesized MnFe 2 O 4 nanoparticles was increased with increase of sonication time and percentage amplitude of ultrasonic power input. The occupational formula by X-ray photoelectron spectroscopy for prepared spinel ferrite nanoparticles was (Mn 0.29 Fe 0.42)[Mn 0.71 Fe 1.58 ]O 4 and (Mn 0.28 Fe 0.54) [Mn 0.72 Fe 1.46 ]O 4 at sonication time 20 min and 80 min, respectively. The value of the saturation magnetization was increased from 1.9 emu/g to 52.5 emu/g with increase of sonication time 20 min to 80 min at constant 50% amplitude of ultrasonic power input, whereas, it was increased from 30.2 emu/g to 59.4 emu/g with increase of the percentage amplitude of ultrasonic power input at constant sonication time 60 min. The highest value of dielectric constant (ε′) was 499 at 1 kHz for nanoparticles at sonication time 20 min, whereas, ac conductivity was 368 × 10−9 S/cm at 1 kHz for spinel ferrite nanoparticles at sonication time 20 min. The demonstrated controllable physical characteristics over sonication time and percentage amplitude of ultrasonic power input are a key step to design spinel ferrite material of desired properties for specific application. The investigation of microwave operating frequency suggest that these prepared spinel ferrite nanoparticles are potential candidate for fabrication of devices at high frequency applications. [ABSTRACT FROM AUTHOR]

Magnetic iron oxide nanoparticles were obtained by a coprecipitation method in a controlled growth process leading to the formation of uniform highly crystalline nanoparticles with average size of 13 nm, which corresponds to the superparamagnetic state. Nanoparticles obtained are a mixture of single-phase nanoparticles of magnetite and maghemite as well as nanoparticles of non-stoichiometric magnetite. The subsequent annealing of nanoparticles at 300 °C in air during 6 h leads to the full transformation to maghemite. It results in reduced value of the saturation magnetization (from 56 emu g −1 to 48 emu g −1 ) but does not affect the heating ability of nanoparticles. A 2–7 wt% dispersion of as-prepared and annealed nanoparticles in glycerol provides high heating rate in alternating magnetic fields allowed for application in magnetic hyperthermia; however the value of specific loss power does not exceed 30 W g −1 . This feature of heat output is explained by the combined effect of magnetic interparticle interactions and the properties of the carrier medium. Nanoparticles coalesce during the synthesis and form aggregates showing ferromagnetic-like behavior with magnetization hysteresis, distinct sextets on Mössbauer spectrum, blocking temperature well about room temperature, which accounts for the higher energy barrier for magnetization reversal. At the same time, low specific heat capacity of glycerol intensifies heat transfer in the magnetic dispersion. However, high viscosity of glycerol limits the specific loss power value, since predominantly the Neel relaxation accounts for the absorption of AC magnetic field energy. [ABSTRACT FROM AUTHOR]