Idza Riati Ibrahim

Influence of Milling Time on the Crystallization, Morphology and Magnetic Properties of Polycrystalline Yttrium Iron Garnet

The polycrystalline Yttrium Iron Garnet (YIG) powder with the chemical formula Y3Fe5O12 has been synthesized by using High Energy Ball Milling technique. The effect of various preparation parameters on the crystallinity, morphology and complex permeability of YIG, which includes milling time and annealing temperature were studied respectively by using XRD, SEM and Impedance Material Analyzer. The frequency dependence of complex permeability namely real permeability, µ’ and magnetic loss, µ’’ were measured at room temperature for samples sintered from 600°C to 1400°C, in the frequency range 10 MHz to 1 GHz. The results showed that milling time plays a role in determining the crystallinity of the milled powder where higher milling time results in better crystallinity due to high reactivity of the particles. From complex permeability measurement, it was observed that the initial permeability and magnetic loss increased with increasing grain size. The permeability values increased with annealing temperature and the absolute values of permeability decreased after attaining the natural resonance frequency of the material.

Microstructural and Dielectric Properties of Zr Doped Microwave Sintered Synthesized by Sol-Gel Route

Polycrystalline samples with the chemical formula CaCu3O12 (, 0.02, 0.1, 0.2, 0.5, and 0.1) CCTZO were synthesized from metal nitrate solutions by the sol-gel method, followed by conventional and microwave heat treatments. The X-ray diffraction pattern of powder calcined at 800°C in conventional furnace for 3 h showed formation of a single phase. The crystal structure did not change on doping with zirconium and it remained cubic in the five studied compositions. The surface morphology of samples sintered at 1000°C in microwave furnace for 10 min was observed using a high resolution scanning electron microscope (HR-SEM). The grain sizes were in the range of 250 nm–5 μm for these samples. HRSEM results show that doping with Zr enhanced grain growth or densification. Energy dispersive X-ray spectroscopy (EDX) confirmed the presence of Zr. The dielectric characteristics of Zr doped CCTO were studied with an LCR meter in the frequency range of 50 Hz–1 MHz. A very high dielectric constant 21,500 was observed for the sample doped with Zr (0.02 mol%) at 50 Hz.

Magnetic and Microwave Properties of Polycrystalline Gadolinium Iron Garnet

The microwave loss in nanosized GdIG particles synthesized using mechanical alloying technique was investigated. There were very few of research on the microwave properties of nanosized particle GdIG and there is no attempt investigating on the material at C-band frequency range and its correlation with the microstructure. Gadolinium (III) iron oxide and iron (III) oxide, α-Fe2O3 were used as the starting materials. The mixed powder was then milled in a high-energy ball mixer/mill SPEX8000D for 3 hours. The samples were sintered at temperature 1200°C for 10 hours in an ambient air environment. The phase formation of the sintered samples was analyzed using a Philips X’Pert Diffractometer with Cu-Kα radiation. Complex permeability constitutes of real permeability and magnetic loss factor were measured using an Agilent HP4291A Impedance Material Analyzer in the frequency range from 10 MHz to 1 GHz. A PNA-N5227 Vector Network Analyzer (VNA) was used to obtain the information on ferromagnetic linewidth broadening, ΔH that represents the microwave loss in the samples in in frequency range of 4 to 8 GHz (C-band). The ΔH value was calculated from the transmission (S21) data acquired from VNA. The single phase GdIG showed low initial permeability and low magnetic loss when applied with low-frequency range energy. From these data, it is validated that GdIG is a suitable material for microwave devices for the high-frequency range.

Influence of Microstructural Evolution on the Magnetically Group Dominance in Polycrystalline Y3Fe5O12 Multi-Samples

In present work, the effect of changing microstructure on magnetic properties which evolves in parallel, in particular from amorphous-to-crystalline development, in yttrium iron garnet was investigated. 9 toroidal samples of polycrystalline yttrium iron garnets were prepared by using the mechanical alloying technique and sintered at low to high sintering temperature for microstructure-dependent-magnetic evolutions. A brief, yet revealing characterization of the samples were carried out by using an X-ray Diffraction, Field Emission Scanning Electron Microscopy, Impedance Material Analyzer, LCR-meter and, Picoammeter. It is believed that microstructural features such as amorphous phase, grain boundary, secondary phase and intergranular pores contribute significant additional magnetic anisotropy and demagnetizing fields, thus affecting the initial permeability accordingly. A scrutinizing observation of the permeability component results show that they tend to fall into three groups of magnetic permeability according to degree of magnetic behaviour dominance. The Curie temperature remained relatively stable and unaffected by the evolution, thus confirming its intrinsic character of being dependent only on the crystal structure and compositional stoichiometry. The increased electrical resistivity while the microstructure was evolving is believed to strongly indicate improved phase purity and compositional stoichiometry.

Influence of sintering temperature on the structural, electrical and microwave properties of yttrium iron garnet (YIG)

This study investigates the structural, electrical and microwave properties of yttrium iron garnet (YIG) which focuses on the parallel evolving relationship with their dependence on the sintering temperature. The iron oxide obtained from the steel waste product (mill scale) was used to synthesize YIG. The raw mill scale underwent the milling and Curie temperature separation technique to produce high purity iron oxide powder which is the main raw material in preparing and fabricating YIG through high energy ball milling (HEBM) process. Microstructural features such as amorphous phase, grain boundary, secondary phase and intergranular pores contribute significantly to the additional magnetic anisotropy and demagnetizing fields, affecting the electric and microwave properties accordingly. The increment in electrical resistivity and decrement in linewidth while the microstructure was evolving is believed to be a strong indicator of improved phase purity and compositional stoichiometry.

Influence of Parallel Evolving Microstructure on Thermal Diffusivity in Strontium Titanate

This paper reports some research findings on the parallel evolutions of microstructural properties and thermal diffusivity in strontium titanate. Strontium titanate samples have been prepared via the high energy ball milling technique and subsequently moulded by a hydraulic pressing and followed by cold isostatic pressing. Nanometer-sized compacted powder samples were sintered from 500 to 1400°C using 100°C increments. Strontium titanate formation was observed at as early as 500°C sintering temperature alongside secondary phases. The full formation of strontium titanate was observed at 800°C sintering temperature and above. Average grain sizes showed a fluctuating trend with increased sintering temperatures due to carbonate decomposition at lower sintering temperatures (500 to 800°C) and grain growth phenomenon at higher sintering temperatures (900 to 1400°C). Parallel characterization of evolving thermal diffusivity showed the same trend of fluctuation at low sintering temperatures as indirect relationship but increased with increased grain size due to a lesser amount of phonon scattering. However, thermal diffusivity values decreased with increased temperatures because of increased phonon-phonon scattering.

MICROWAVE ABSORPTION CHARACTERISTICS OF SOME FERRITE- FILLED POLYMER COMPOSITES

Prior to their use for microwave absorption, different compositions of NixZn1-xFe2O4 (x = 0.5, 0.6, 0.7 and 0.8) were prepared via mechanical alloying and sintering. X-ray diffractometry (XRD) was used to investigate the crystalline phase formation. Scanning transmission electron microscopy (STEM) and field emission electron microscopy (FeSEM) were used to investigate the particle size and surface morphology respectively. The complex-permeability components, μʹ and μʺ, were also measured using an Agilent 4291B material analyzer from 1 MHz to 1 GHz. From the XRD results it is shown that at 900oC the full phase of nickel zinc ferrite was formed. The μʺ values suggest that the ferrite sample can absorb well microwave energy for frequencies 1 MHz to 1 GHz and higher. This is proved by microwave absorption measurements carried out up to 12 GHz.Keywords: NiZn-ferrite, microwave absorption, magnetic materials