K. Sadhana

Effect of pH on structural and magnetic properties of nanocrystalline Y3Fe5O12 by aqueous co-precipitation method

Abstract The Y3Fe5O12 (YIG) nanopowders were synthesised at different pH using co-precipitation method. The effect of pH on the phase formation of YIG is characterised using XRD, TEM, FTIR and TG/DTA. From the Scherer formula, the particle sizes of the powders were found to be 13, 19 and 28 nm for pHu200a=u200a10, 11 and 12 respectively. It is found that as the pH of the solution increase the particle size is also increases. It is also clear from the TG/DTA curves that as the pH is increasing the weight losses were found to be small. The nanopowders were sintered at 600, 700, 800 and 900°C for 5 h using conventional sintering method. The phase formation is completed at 800°C/5 h which is correlated with TG/DTA. The average grain size of the samples is found to be ∼161 nm. The high values of Msu200a=u200a23 emu g−1 and Hcu200a=u200a22 Oe were recorded for the sample sintered at 900°C.

Microwave sintering of nickel ferrite nanoparticles processed via sol–gel method

Magnetic nickel ferrite (NiFe2O4) was prepared by sol–gel process and calcined in the 2.45xa0GHz singlemode microwave furnace to synthesize nickel nanopowder. The sol–gel method was used for the processing of the NiFe2O4 powder because of its potential for making fine, pure and homogeneous powders. Sol–gel is a chemical method that has the possibility of synthesizing a reproducible material. Microwave energy is used for the calcining of this powder and the sintering of the NiFe2O4 samples. Its use for calcination has the advantage of reducing the total processing time and the soak temperature. In addition to the above combination of sol–gel and microwave processing yields to nanoscale particles and a more uniform distribution of their sizes. X-ray diffraction, energy dispersive X-ray spectroscopy, transmission electron microscopy and vibrating sample magnetometer were carried out to investigate structural, elemental, morphological and magnetic aspects of NiFe2O4. The results showed that the mean size and the saturation magnetization of the NiFe2O4 nanoparticles are about 30xa0nm and 55.27xa0emu/g, respectively. This method could be used as an alternative to other chemical methods in order to obtain NiFe2O4 nanoparticles.

Effect of Sm3+ on dielectric and magnetic properties of Y3Fe5O12 nanoparticles

The Sm3+ doped Y3−xSmxFe5O12 (xxa0=xa00–3) nanopowders were prepared using modified sol–gel route. The crystalline structure and morphology was confirmed by X-ray diffraction and atomic force microscopy. The nanopowders were sintered at 950xa0°C/90xa0min using microwave sintering method. The lattice parameters and density of the samples were increased with an increase of Sm3+ concentration. The room temperature dielectric (ε′ and ε″) and magnetic (μ′ and μ″) properties were measured in the frequency range up to 20xa0GHz. The room temperature magnetization studies were carried out using Vibrating sample magnetometer using filed of 1.5 T. Results of VSM show that the saturation and remnant magnetization of Y3−xSmxFe5O12 (0–3) decreases on increasing the Sm concentration (x). The low values of magnetic (μ′ and μ″) properties makes them a good candidates for microwave devices, which can be operated in the high frequency range.

Structural and magnetic properties of nanocrystalline BaFe12O19 synthesized by microwave-hydrothermal method

Nanocrystalline BaFe12O19 powders were prepared by microwave-hydrothermal method at 200xa0°C/45xa0min. The as-synthesized powders were characterized by using X-ray diffraction (XRD), thermogravimetry (TG) and differential thermal analysis (DTA). The present powders were densified at different temperatures, i.e., 750, 850, 900 and 950xa0°C for 1xa0h using microwave sintering method. The phase formation and morphology studies were carried out using XRD and field emission scanning electron microscopy (FE-SEM). The average grain sizes of the sintered samples were found to be in the range of 185–490xa0nm. The magnetic properties such as saturation magnetization and coercive field of sintered samples were calculated based on magnetization curves. A possible relation between the magnetic hysteresis curves and the microstructure of the sintered samples was investigated.

Development of nanocrystalline Mn–Zn ferrites for forward type DC–DC converter for switching mode power supplies

Abstract Nanocrystalline Mn–Zn ferrites have been successfully synthesised using the microwave–hydrothermal method for high frequency applications. The nanopowders were characterised using X-ray diffraction (XRD) and transmission electron microscopy (TEM). They were annealed using the microwave sintering method at 900°C for 20 min. The frequency dependence of the dielectric constant ϵ′ and and the initial permeability μ i were measured in the range 10 Hz to 1·3 GHz. The saturation magnetisation M s and coercive force H c were obtained using a vibration sample magnetometer (VSM) in the field of 20 kOe. The total power loss was measured in the range of 100 kHz to 1 MHz with a flux density of 50 mT on the annealed samples. Conductor-embedded ferrite transformers were fabricated and the output power P o and efficiency η were measured; 80% efficiency was obtained for a forward-type multilayered transformer.

Fabrication of dc–dc converter using nanocrystalline Mn–Zn ferrites

Abstract The microwave–hydrothermal method has been successfully used for synthesis of nanocrystalline Mn–Zn ferrites which are used for high frequency applications. The nanopowders were characterised using X-ray diffraction and TEM. The nanopowders were annealed using microwaves at 600°C/10 min. The frequency dependence of dielectric constant ϵ′ was measured in the range from 10 Hz to 1·3 GHz, and initial permeability μ i was measured in the range from 10 Hz to 1 MHz. The total power loss was measured at 100 kHz and 200 mT on the annealed samples. Conductor embedded ferrite transformers were fabricated, and output power P o, efficiency η and temperature increase ΔT were measured at sinusoidal voltage of 25 V with frequency 1 MHz. The transformer efficiency η was found to be high, and surface rise of temperature ΔT is very low.

DIELECTRIC AND MAGNETIC PROPERTIES OF BaTiO3+MgCuZnFe2O4 NANOCOMPOSITES

Nanocrystalline MgCuZnFe2O4 and BaTiO3 powders were synthesized using the microwave hydrothermal (M-H) method at 160°C for 45 min for the preparation of xBaTiO3+(1-x)MgCuZnFe2O4. The nanopowders were characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The particle size of the powders was found to be ~30 and ~40 nm for MgCuZnFe2O4 and BaTiO3, respectively. The nanopowders were mixed at different weight percentages and densified at 910°C for 30 min using the microwave sintering method. The sintered composites were characterized using XRD and scanning electron microscopy (SEM). The density of the composites varies 93–96% of theoretical density. The density of the present composites increases as the weight percentage of BaTiO3 content increases. The frequency variation of dielectric constant (e), dissipation factor (D), initial permeability (μi) and quality factor (Q) were measured from 1 kHz to 1 MHz.

Synthesis and characterization of some ferrite nanoparticles prepared by co-precipitation method

Two different compositions of ferrites namely Ni0.53Cu0.12Zn0.35Fe2O4 and Mg0.2Cu0.3Zn0.5Fe2O4 have been synthesized by co-precipitation method and sintered at 900xa0°C/5h. The prepared samples are analyzed for their structural, morphology, elemental composition and magnetic properties by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray fluorescence and vibrating sample magnetometer respectively. Spinel phase, along with the hematite as an additional phase, in both samples is confirmed from the XRD characterizations results. Rietveld refinement method is employed to analyze the structural parameters of the samples. Density and saturation magnetization have found to be increased from that of undoped sample values. Homogeneous distributions of particles and well defined particle sizes are revealed from SEM studies of the samples. Maximum entropy method is employed to compute the numerical value of various sites interactions in ferrites and the findings are compared and analyzed with that of magnetic studies.

SYNTHESIS OF NANOCRYSTALLINE YIG USING MICROWAVE-HYDROTHERMAL METHOD

The aim of present research is to study the influence of sintering temperature on the preparation of nanocrystalline Yttrium Iron garnet (YIG) with improved magnetic properties. The nanocrystalline YIG powders were synthesized using Microwave-Hydrothermal (M-H) method. The synthesized powders were characterized using X-ray diffraction (XRD) and Transmission Electron Microscope (TEM). The powders were sintered at various temperatures using microwave sintering method. The sintered samples were characterized using XRD. The complex permeability, dielectric constant and loss tangent of sintered YIG ceramic were also measured and discussed in this paper

Structural and magnetic properties of nanocrystalline Y3Fe5O12 using co-precipitation method

The Y3Fe5O12 (YIG) nanopowders were synthesized using Co-precipitation method. The single phase YIG nano powders are synthesized at a low sintering temperature of 800°C and the grain size is found to be close to the critical diameter for the single domain to multidomain crossover. The values of Ms = 20emu/g and Hc= 76Oe were observed for the sample sintered at 800°C.