T. Ramesh

Low Temperature Sintering of YIG Using Microwave Sintering Method

The pure YIG samples were prepared using microwave sintering method. The samples were sintered by using two types of sintering methods conventional and microwave. The sintered samples were characterized using XRD and SEM. The microwave sintering method was observed to be superior to conventional sintering process in the densification of pure YIG samples. In the present investigation a theoretical density of 98% has been achieved with pure garnet phase with smaller grain size. The sintering temperature and soaking time was reduced from 1300°C/10 hr to 1100°C/30 min. The saturation magnetization has been measured and obtained resutis presented and discussed The ferromagnetic resonance line width has been measured at room temperature.

Nanocrystalline Ni-Al ferrites for high frequency applications

Nanocrystalline Ni0.94Co0.03Mn0.04Cu0.03Fe1.96-xAlxO4(x = 0,0.1,0.3,0.5,0.7and0.9) were synthesized using microwave hydrothermal method at 160°C/40 min. The synthesized powders were characterized using XRD, TEM and FTIR. The nanopowders were sintered using microwave sintering method at 950°C/30 min. The prepared samples were characterized using XRD and SEM. The substitution of Al3+ ions in place of Fe3+ ions results decrease of the density and lattice constant. The increase in D.C resistivity and reduction in the initial permeability, Ms and TC has been observed with an increase of Al3+ ions. High D.C resistivity, thereby decrease in the dielectric losses and an excellent temperature stability of Magnetization (4πMs) are desired characteristics of ferrites used for fabrication of microwave devices.

Composites: Preparation and Magnetodielectric Properties

Cobalt ferrite (CoFe2O4) and silica (SiO2) nanopowders have been prepared by the microwave hydrothermal (M-H) method using metal nitrates as precursors of CoFe2O4 and tetraethyl orthosilicate as a precursor of SiO2. The synthesized powders were characterized by XRD and FESEM. The ( ) (CoFe2O4) + SiO2 (where = 0%, 10%, 20%, and 30%) composites with different weight percentages have been prepared using ball mill method. The composite samples were sintered at 800°C/60 min using the microwave sintering method and then their structural and morphological studies were investigated using X-ray diffraction (XRD), Fourier transformation infrared (FTIR) spectra, and scanning electron microscopy (SEM), respectively. The effect of SiO2 content on the magnetic and electrical properties of CoFe2O4/SiO2 nanocomposites has been studied via the magnetic hysteresis loops, complex permeability, permittivity spectra, and DC resistivity measurements. The synthesized nanocomposites with adjustable grain sizes and controllable magnetic properties make the applicability of cobalt ferrite even more versatile.

Effect of aluminum substitution on structural and electromagnetic properties of nanocrystalline MgCuMn ferrites

The effect of substitution of nonmagnetic Al3+ ions on the structural and electromagnetic properties were studied in nanocrystalline ferrite series of Mg0.8Cu0.2AlxFe1.95-xMn0.05O4 where x varies 0-0.4 in steps of 0.1. This series was synthesized by using microwave hydrothermal method. The nanocrystalline ferrite phase was observed at temperature 150°C/40 min. Synthesized powders were characterized using X-ray diffraction (XRD) and transmission electron microscopy (TEM). The synthesized powders were densified using microwave sintering method at 950°C/40 min. The sintered samples were characterized using XRD. Surface morphology was observed by using field effective scanning electron microscopy (FESEM). The electrical and magnetic properties were measured at room temperature. These results led us to interfere that the values of d.c resistivity increases and dielectric constant, initial permeability, saturation magnetization and Curie temperature were observed to be decreased with the substitution of Al3+ io...

Electrical and dielectric properties of xNi 0.53 Cu 0.12 Zn 0.35 Fe 1.88 O 4 + (1−x) BaTiO 3 nanocomposites

The composite of xNi<inf>0.53</inf>Cu<inf>0.12</inf>Zn<inf>0.35</inf>Fe<inf>1.88</inf>O<inf>4</inf>+(1−x)BaTiO<inf>3</inf> were prepared by mixing nanocrystalline Ni<inf>0.53</inf>Cu<inf>0.12</inf>Zn<inf>0.35</inf>Fe<inf>1.88</inf>O<inf>4</inf> and BaTiO<inf>3</inf> powders at different weight percent. The powders were densified using microwave sintering method at 900°C/30min. The phase and morphology of the composites was observed with X-ray diffraction (XRD) and Scanning Electron Microscope (SEM). The frequency dependence of real (ε′) and imaginary (ε″) parts of permittivity was measured in the range of 1MHz–1.8GHz. The values of ε′ increases with an increase of BaTiO<inf>3</inf> content at 1MHz. The experimental value of dielectric constant was compared with available theoretical models. The transition temperature (T<inf>C</inf>) of composite materials decreases with an increase of BaTiO<inf>3</inf> content.