Yttrium-(Y) substituted Mg-Zn ferrites with the compositions of Mg 0.5 Zn 0. 5Y x Fe 2-x O 4 (0 ≤ x ≤ 0.05) have been synthesized by conventional standard ceramic technique. The effect of Y 3+ substitution on the structural, electrical, dielectric and magnetic properties of Mg-Zn ferrites has been studied. The single phase of spinel structure with a very tiny secondary phase of YFeO 3 for higher Y contents has been detected. The theoretically estimated lattice constant has been compared with measured experimental lattice constant. The bulk density, X-ray density and porosity have been calculated. The Energy Dispersive X-ray Spectroscopy (EDS) study confirms the presence of Mg, Zn, Y, Fe and O ions in the prepared samples. Frequency dependence of conductivity has been studied and an increase in resistivity (an order) has been observed. Frequency dependence of dielectric constant (ԑʹ), dielectric loss tangent (tanδ) has been studied and the lowering of ԑʹwith the increase of Y content was noted. Dielectric relaxation time was found to vary between 15 to 31 nano seconds. The saturation magnetization (M s ), coercive field (H c ), remanent magnetization (M r ) and Bohr magneton (µ B ) have been calculated. The variation of M s has been successfully explained with the variation of A-B interaction strength due to Y substitution. The soft ferromagnetic nature also confirmed from the values of H c . The complex permeability has been studied and the initial permeability was found to increase with Y up to x = 0.01, thereafter it decreases. The values of electrical resistivity and dielectric constant with proper magnetic properties suggest the suitability of Y-substituted Mg-Zn ferrites in microwave device applications.
Abstract-Radio-frequency inductively coupled plasma in a pulse modulated approach was generated by a MOSFET inverter supply of high electric efficiency. The plasma torch has an extremely long coil region of 153 mm, which is an attractive feature for advanced materials processing, especially for better and more efficient vaporizing of solids. The operating conditions were: argon flow of 80 or 90 L/m at atmospheric pressure; supply power of 30 kW; and pulse on-time of 10 ms at 67% duty factor. Spectroscopic measurements were carried out to determine the temporal plasma properties, including the effects of shimmer current level (SCL) upon the spectral intensities. Additionally, a time-dependent two-dimensional numerical model was solved for the same operating conditions employed in the experiment to predict and compare the plasma properties. Pulsed plasma dissipation sustained for a minimum SCL of 43% for 80 L/m gas flow-rate, and at any level below 43%, the plasma disappeared. Temporal variation of argon line intensities at 751 and 763.5 nm is similar, though the upper level intensity of the former one was significantly stronger than the latter. Intensified change of intensity is found at lower SCL because of higher change in the coil current and, in turn, in the plasma power. The predicted intensity of the 751-nm argon line showed similar behavior to the experimental intensity though the response around the instant of on-pulsation is somewhat slower.
Zinc substituted cobalt ferrite nanoparticles with elemental composition Co[Formula: see text]ZnxFe2O4 ([Formula: see text], 0.2, 0.4, 0.6) were prepared by the sol-gel auto-combustion technique using Co, Fe, Zn nitrate as a precursor where nitrates to citrate was 1:3. The as prepared powder of cobalt zinc ferrite was sintered at 900∘C for 3[Formula: see text]h. Structural, morphological, dielectric and magnetic properties were studied by x-ray diffractometer (XRD), scanning electron microscope (SEM), high precision impedance analyzer and vibrating sample magnetometer (VSM), respectively. The peaks obtained from the XRD confirmed samples having crystallite ([Formula: see text]32–36[Formula: see text]nm) single phase inverse spinel structure without any traceable impurity. Lattice parameters were calculated from XRD and it increases with Zn content. SEM revealed irregularly shaped grains ([Formula: see text]–0.7[Formula: see text][Formula: see text]m) morphology with heterogeneous distribution. The dielectric constant ([Formula: see text]) and dielectric loss ([Formula: see text]), have been measured as a function of frequency at room temperature. The dependence of [Formula: see text] and [Formula: see text] with frequency showed the normal dielectric behavior in accordance with the Maxwell-Wagner type of interfacial polarization and electron hopping change between Co[Formula: see text] and Co[Formula: see text] as well as between Fe[Formula: see text] and Fe[Formula: see text] ions at octahedral sites.
A pulse-modulated rf inductively coupled thermal plasma, which has extended control in its applications in pulse mode, was diagnosed both experimentally and numerically to determine the critical values of the duty factor and shimmer current level down to which the pulse mode of the plasma is sustained. Pulse-modulated plasmas were generated for different operating conditions (at atmospheric pressure, 2-20 ms on-time, 60-70% shimmer current level) and corresponding spectroscopic measurements were carried out. For different pulse on-times, the limit of the respective off-times for which pulse mode of plasma exists were determined and, thus, a typical operating zone of pulse-modulated plasma was proposed in both experimental and theoretical efforts. A two-dimensional model was solved numerically at atmospheric pressure (760 Torr) with various duty factors and shimmer current levels. A portion of theoretically predicted results were compared with the experimental results where reasonable agreement was found.
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