Mustaffa Hj Abdullah

Electromagnetic and absorption properties of some microwave absorbers

Electromagnetic properties of a thermoplastic natural rubber (TPNR), a lithium–nickel–zinc (Li–Ni–Zn) ferrite and a TPNR–ferrite composite subjected to transverse electromagnetic (TEM) wave propagation were investigated. The incorporation of the ferrite into the matrix of the TPNR was found to reduce the dielectric loss but the magnetic loss increased. The absorption characteristics of all the samples subjected to a normal incidence of TEM wave were investigated based on a model of a single-layered plane wave absorber backed by a perfect conductor. It is evident from a computer simulation that the ferrite is a narrowband absorber, whereas the polymeric samples show broadband absorption characteristics. Minimal reflection of the microwave power or matching condition occurs when the thickness of the absorbers approximates an odd number multiple of a quarter of the propagating wavelength. This is discussed as due to cancellation of the incident and reflected waves at the surface of the absorbers. The Li–Ni–Z...

Complex impedance and dielectric properties of an MgZn ferrite

Abstract Complex impedances of a sintered polycrystalline Mg 0.5 Zn 0.5 Fe 2 O 4 ferrite in the frequency range of 15 mHz to 13 MHz were measured at several temperatures in the range of 273–373 K. The complex-plane impedance spectra indicate that the material can be represented by a two-layer leaky capacitor which corresponds to the bulk and the grain boundary phenomena at high and low frequencies respectively. A series resistance of about the same value at all temperatures is observed. This resistance is believed to be due to the external contacts and the electrodes. Agreement between experimental and simulated data is established by assuming a frequency-dependent capacitive element. The results for the relative dielectric constant ϵ ′ r and dielectric loss ϵ ′ r at low frequencies are discussed as being attributed to the interfacial polarization; at high frequencies a Debye-like relaxation from orientational polarization is dominant. The dependence of impedance and dielectric properties on temperature and frequency are discussed.

Effect of nickel-cobalt-zinc ferrite filler on electrical and mechanical properties of thermoplastic natural rubber composites

ABSTRACT Thermoplastic natural rubber (TPNR) as polymer matrix was prepared by the melt blending method. Nickel-cobalt-zinc (NiCoZn) ferrite as a filler was prepared by the double-stage sintering method in air. The filler was incorporated in the polymer matrix using a Brabender internal mixer. The filler content was varied from 0 to 30 wt.%. The morphological study of the fractured surface using a scanning electron microscope (SEM) shows the effects of strain. The X-ray diffraction (XRD) indicates the coexistence of both the ferrite and thermoplastic. Electrical properties were studied using a high frequency response analyzer (HFRA) at room temperature (298°K). The results show that resistivity (ρ) decreases, but the dielectric constant increases, with increasing filler content. The resistivity and dielectric constant for all the composites are in the range of 8.9 × 106–9.7 × 105 Ωm and 33–72, respectively. A sharp change in both quantities around 15 wt.% filler content is interpreted as due to the transition from a dispersed system to an attached system. The tensile study shows that the elongation at break point and the tensile strength of the composite at room temperature decrease with increasing filler content. The hardness of the samples decreases with increasing filler content.

Effect of nickel-cobalt-zinc ferrite filler on magnetic and thermal properties of thermoplastic natural rubber composites

A sample of Ni0.25Co0.25Zn0.5Fe2O4 ferrite was prepared by a double-staged sintering method in air. Thermoplastic natural rubber (TPNR) was prepared by melt blending of natural rubber (NR), liquid natural rubber (LNR), and high density polyethylene (HDPE) in an internal mixer Brabender Plasticorder PL 2000. Magnetic polymer composites were prepared from the ferrite and TPNR matrix using the same melt blending method at 135°C with mixing rate of 50 r.p.m. for 12 min. The fillers were varied from 5 to 30 weight percent. A uniform dispersion of the filler in the matrix was confirmed by thermogravimetric analysis (TGA). The density of the composites was determined using densitometer MD 200S. Magnetic properties were studied using a vibrating sample magnetometer (VSM) at room temperature (25°C). The results show that magnetization (M), saturation magnetization (MS), remanent magnetization (MR), initial susceptibility (χi) and initial permeability (μi) increase with increasing filler content at all compositions. The composites can be classified as soft magnetic materials as their coercivities are in the range of 30–36 Oe. The differential scanning calorimetric (DSC) results indicate that the glass transition temperature (Tg) and the melting point (Tm) of all the composites are independent of the filler content. The thermal conductivity of the composites was found to be in the range of 0.26 to 0.52 W m−1 K−1.

The Effect Of Temperature On Magnetic Behavior Of Magnetite Nanoparticles And Its Nanocomposites

The magnetic properties of magnetite nanoparticles and magnetite‐thermoplastic natural rubber (TPNR) nanocomposites was prepared by melt‐blending method has been studied using vibrating sample magnetometer (VSM). The saturation magnetization (MS), remanence (MR), squareness (MR/MS), coercivity (HC) and exchange‐bias field (Heb) for magnetite nanoparticles and its nanocomposites increased with decreasing temperature from 298 to 93 K. The increment of magnetization might be due to the decrease in thermal energy while the enhancement of coercivity and exchange‐bias field is attributed to the exchange interaction at the interface between the ferrimagnetic (Fe3O4) and spin‐glass‐like surface layer on the nanocrystalline magnetite.

Effects of Annealing Temperature on Structure and Magnetic Properties ofTbxY3−xFe5O12(x=0.2and 0.4) Thin Films

Terbium-substituted yttrium iron garnet (TbxY3-xFe5O12 (x = 0.2 and 0.4)) thin films have been successfully prepared by a sol-gel method followed by spin-coating process. The annealing of the films was performed at different temperatures like 700, 800, and 900°C and found that the films annealed at 900°C turned out to be crystallized into a pure garnet phase. All of the films were bearing grains of nanometer in size. Increasing the annealing temperature gave extra energy to the grains causing to be agglomerates. The lattice contraction occurred as the grains sizes were decreased due to the decrease of Fe2+ formation. The magnetic measurements show that all of the films are soft magnetic materials with low saturation magnetization values. The hysteresis loops of the films which were annealed at 900°C were found angular in shape similar to the single crystal-like YIG film.

Effects of annealing temperature on structure and magnetic properties of Tb x Y 3-x Fe 5 O 12 ( x = 0.2 and 0.4) thin films

Terbium-substituted yttrium iron garnet (TbxY3-xFe5O12 (x = 0.2 and 0.4)) thin films have been successfully prepared by a sol-gel method followed by spin-coating process. The annealing of the films was performed at different temperatures like 700, 800, and 900°C and found that the films annealed at 900°C turned out to be crystallized into a pure garnet phase. All of the films were bearing grains of nanometer in size. Increasing the annealing temperature gave extra energy to the grains causing to be agglomerates. The lattice contraction occurred as the grains sizes were decreased due to the decrease of Fe2+ formation. The magnetic measurements show that all of the films are soft magnetic materials with low saturation magnetization values. The hysteresis loops of the films which were annealed at 900°C were found angular in shape similar to the single crystal-like YIG film.

Structure and Magnetic Properties of Fe5O12 (, and 2.0) Thin Films Prepared by Sol-Gel Method

Nanoparticles Fe5O12 (, 1.0, and 2.0) thin films were prepared by sol-gel method and treated at 800, 900, and 1000∘C, respectively, for 2 h. The films have single phase garnet structure and the sizes of particles are in the range of 44 to 83 nm. The magnetic measurements show that the saturation magnetization decreased with increasing of Er concentration for all samples treated at different annealing temperatures. The saturation magnetization increased with the particle size due to the enhancement of the surface spin effect. The coercivity initially decreased for and then increased for with increasing annealing temperature.

Effects of Annealing Temperature on Structure and Magnetic Properties of TbY3−Fe5O12 (=0.2 and 0.4) Thin Films

Terbium-substituted yttrium iron garnet (TbxY3-xFe5O12 (x = 0.2 and 0.4)) thin films have been successfully prepared by a sol-gel method followed by spin-coating process. The annealing of the films was performed at different temperatures like 700, 800, and 900°C and found that the films annealed at 900°C turned out to be crystallized into a pure garnet phase. All of the films were bearing grains of nanometer in size. Increasing the annealing temperature gave extra energy to the grains causing to be agglomerates. The lattice contraction occurred as the grains sizes were decreased due to the decrease of Fe2+ formation. The magnetic measurements show that all of the films are soft magnetic materials with low saturation magnetization values. The hysteresis loops of the films which were annealed at 900°C were found angular in shape similar to the single crystal-like YIG film.