Influence of shape anisotropy on microwave complex permeability in carbonyl iron flakes/epoxy resin composites

To explore the mechanism of carbonyl iron flake composites for microwave complex permeability, this paper investigates the feature of the flakes. The shape anisotropy was certified by the results of the magnetization hysteresis loops and the Mossbauer spectra. Furthermore, the shape anisotropy was used to explain the origin of composite microwave performance, and the calculated results agree with the experiment. It is believed that the shape anisotropy dominates microwave complex permeability, and the natural resonance plays main role in flake.

Complex Permeability of Ferrites as Intrinsic and Extrinsic Properties

CIP （complex initial permeability） spectra of PF （polycrystalline ferrite） are studied both as intrinsic and extrinsic properties. In the former case, main steps of modeling, based on effects coming from polycrystal grain sizes distribution and defects, are described. The obtained relations work well in practice for PF with more or less normal MS （microstructure） and no size effects. Besides, fundamental connection between parameters of CIP and MS is found. Another case--PF with possible size effects （MnZn-ferrites） are studied experimentally for different sizes of cores, unveiling the dependence of phenomena on： dimensions of cross-section, number of turns, width of nonmagnetic gap.

Effects of Nd^(3+)on the microstructure and magnetic properties of Ni-Zn ferrites

Ni0.4Zn0.6Fe2-xNdxO4（x = 0-0.07） ferrites doped with different amounts of Nd2O3 were prepared using standard ceramic technique. The samples were uniaxially pressed and sintered at 1250℃ for 4 h in air. The phase structure and microstructure of the samples were investigated using X-ray diffraction and scanning electron microscope, respectively. The complex permeability was measured using the impedance analyzer in the range of 1-100 MHz. The results indicate that with increasing Nd^3＋ content, the relative density and lattice parameter a of the sintered samples increase, whereas the real part of permeability （μ′） and the magnetic loss tangent （tan δ） decrease. The substitution of Nd^3＋ for Fe^3＋ forms a secondary phase on the grain boundary of the matrix, which strongly restrains the grain growth of the matrix.

Preparation, Microstructure and Magnetic Properties of NiZn Ferrite Thin Films by Spin Spray Plating

NiZn ferrite thin fihns were performed on glass substrates of 85 ℃ by spin spray plating method. X-ray diffraction patterns of the films show that the samples have a cubic spinel structure with no extra lines corresponding to any other phases between 75 ℃ and 85 ℃. As the pH value of oxidizing solution increases to 8.3, the saturation magnetization increases to 3.13 × 10^5 A/m and resistivity to 127 m Ω ·cm. Film deposited at pH 7.8 has a smooth surface and definite columnar structure. The large wavy flakes were observed at pH 8.3. The high real part of complex permeability μ′ up to 36.1 and the imaginary part μ″ up to 53.2 were observed at 0.5 GHz by short microstrip line perturbation method. The μ″ of thin film has values higher than 20 at the frequencies between 0.5 GHz and 2 GHz, the film is a promising anti-noise material for high frequency applications,

EFFECT OF Si CONTENT ON ORDERING DEGREE AND ELECTROMAGNETIC CHARACTERISTICS IN FeSiAl ALLOYS

FeSiAl alloys ribbons synthesized by melt-quench were annealed in vacuum at 873 K for 60 rain. The flaky powders were prepared by milling the annealed ribbons for 70 h. After milling, the powders were heat treated at 573 K for 90 rain. The ordering degree of the powders lattice structure was analyzed by X-ray diffraction （XRD）. The measurement of specific saturation magnetization was carried out by vibrating samples magnetometer （VSM）. Complex permittivity and complex permeability in the frequency band of 0.5-18 GHz were measured with the vector network analyzer. The ordering degree of the superlattice structure increased from 0.2＇7 to 0.49. Complex permittivity and complex permeability decreased with increasing Si content. After ordering, the specific saturation magnetization decreased from 134.2 to 85.0 A.m2.kg-1. For use in anti-EMI material, the total contents of Si and Al in FeSiAl alloys should be controlled at a low level.

Structural and Magnetic Studies of CTAC-assisted NiZn Ferrite Films within 0.1-3.5 GHz

Spinel NiZn ferrite thin films were prepared on glass substrates by spray plating method. Adding cetyltrimethylammoniumchloride （CTAC）, adsorptive energy of substrate surface increased, and smooth surface and uniform columnar film structures were observed. The optimum reaction temperature up to 85℃ and pH up to 7.5 were obtained. As the solution pH value increases from 6.5 to 7.5, the film saturation magnetization increases to 36.1 and the imaginary part μ″ up to 53.2 for NiZn ferrite film at 500 MHz were achieved, and higher magnetic resonance at 508 MHz was observed. As the ferrite plate thickness is 50 μm, the attenuating characteristics for reflection loss ≤-0.8 dB can be obtained in the wide frequency ranging from 0.5 to 2.7 GHz. Theμ″ of thin film has values higher than 20 at the frequencies between 0.5 and 2 GHz, and the thin film can be applied as shielding material in GHz range.

Microwave reflection properties of planar anisotropy FesoNi50 powder/paraffin composites

The reflection properties of planar anisotropy FesoNiso powder/paraffin composites have been studied in the microwave frequency range. The permeability of Fe50Ni50 powder/paraffin composites is greatly enhanced by introducing the planar anisotropy, and can be further enhanced by using a rotational orientation method. The complex permeability can be considered as the superposition of two types of magnetic resonance. The resonance peak at high frequency is attributed to the natural resonance, while the peak at low frequency is attributed to the domain-wall resonance. The simulated results of the microwave reflectivity show that the matching thickness, peak frequency, permeability, and permittivity are closely related to the quarter wavelength matching condition. The Fe50Ni50 powder/paraffin composites can be attractive candidates for thinner microwave absorbers in the L-band （1-2 GHz）.

Microwave reflection properties of planar anisotropy Fe_(50)Ni_(50) powder/paraffin composites

The reflection properties of planar anisotropy Fe50Ni50 powder/paraffin composites have been studied in the microwave frequency range.The permeability of Fe50Ni50 powder/paraffin composites is greatly enhanced by introducing the planar anisotropy,and can be further enhanced by using a rotational orientation method.The complex permeability can be considered as the superposition of two types of magnetic resonance.The resonance peak at high frequency is attributed to the natural resonance,while the peak at low frequency is attributed to the domain-wall resonance.The simulated results of the microwave reflectivity show that the matching thickness,peak frequency,permeability,and permittivity are closely related to the quarter wavelength matching condition.The Fe50Ni50 powder/paraffin composites can be attractive candidates for thinner microwave absorbers in the L-band(1-2 GHz).

Sintering Temperature Dependent Magnetic and Dielectric Properties of Polycrystalline xBa_0.95Sr_0.05TiO₃-(1 - x)BiFe_0.90Gd_0.10O₃Ceramics

Polycrystalline xBa0.95Sr0.05TiO3-(1 - x)BiFe0.90Gd0.10O3 ceramics were prepared by standard solid state reaction technique using the solid solution of BaCO3, SrCO3, TiO2, Bi2O3, Fe2O3 and Gd2O3. The compound is a BiFeO3 based multiferroic material which contains both magnetic and electric properties. The synthesized ceramics noticed better properties than xBaTiO3-(1 - x)BiFeO3 because of adding rare earth element Gd which have higher magnetic moment than Fe. The prepared samples were sintered at 900˚C, 950˚C and 1000˚C for 1 h. The effect of sintering temperature on density of the compound, complex initial permeability, dielectric properties and complex impedance analysis was reported in this article. Density of the ceramics was found to be enhanced with the rise in sintering temperature which implied porosity of the compound decreased when sintering temperature was increased. Enhanced complex initial permeability was noticed for the samples up to 950˚C and this might be attributed to reducing the motion of domain wall when the ceramics were sintered above 950˚C. Value of dielectric constant increased whereas dielectric loss decreased and these modifications might be expected because of changing density and grain size due to the variation of sintering temperature. Grain resistance (resistance due to grains) was determined from complex impedance analysis and it reduced with the rise in sintering temperature. The studied multiferroic material exhibited weak ferromagnetism but is an alternative product of environmental hazard lead (Pb) based multiferroic material and it is expected to be environment friendly.

Effect of Cu Incorporation on Structure, Densification and Magnetic Properties of Polycrystalline Li_<i>x</i>Ni_0.2Zn_{0.8-2<i>x</i>}Fe_2+<i>x</i>O₄Ceramics

The polycrystalline LixNi0.2Zn0.8-2xFex+2O4 and LixNi0.1Cu0.1Zn0.8-2xFex+2O4 (x = 0.0, 0.1, 0.2, and 0.3) ferrites were synthesized by the standard solid-state reaction method. The compound was sintered at 1150˚C for 5 hours. The effect of Cu substitution and its impact on the crystal structure, microstructure, complex initial permeability and magnetization of the Ni-Zn ferrites were studied. The effect of Li+ incorporation on the properties mentioned above was also investigated. X-ray diffraction patterns of the samples indicated a single cubic spinel structure for both the compound. No effect of Cu addition on crystal structure was observed. The density of the ferrites was found to be enhanced because of adding Li whereas the porosity of the samples decreased with the content of Li ions. The average value of grain size increased with the addition of Li content. The samples having Cu ions formed bigger size grains. Frequency-dependent complex initial permeability, loss tangent, and relative quality factor were studied at room temperature using an Impedance analyzer in the range of 100 Hz - 120 MHz regions. In the low-frequency region, the prepared samples exhibited a high value of permeability and after a certain frequency, the permeability falls. The value of permeability enhanced with the increase in Li whereas loss tangent was found to be reduced. The relative quality factor graphs described that the compound has excellent frequency stability up to a certain frequency which is suitable to be used in inductors, resistors, capacitors, etc. Initial permeability for LixNi0.1Cu0.1Zn0.8-2xFex+2O4 ferrites was found high than LixNi0.2Zn0.8-2xFex+2O4 which might be attributed to having bigger size grains of Cu containing samples because of easy movement of domain wall in bigger size grains. The values of saturation magnetization (Ms) were calculated for both compounds from M-H hysteresis loops and it enhanced with the increase in Li content which might be related to the modification of predominant exchange interactions between the cations. The Cu-containing compound exhibited higher values of saturation magnetization. The cation distribution reflects this increment because ferromagnetic Ni2+ and paramagnetic Cu2+ ions occupied in the B-sites and the diamagnetic Zn and paramagnetic Li occupied in the A-sites;therefore, net magnetic moments increased gradually. The studied materials might be used as an alternative to Pb-based compounds and would be environment friendly.

Structural, Dielectric, and Magnetic Properties of Ba-Doped Multiferroic Bismuth Ferrite

The main focus of the research was to correlate the microstructure with dielectric and magnetic properties of Bi1-xBaxFeO3 samples. Bi1-xBaxFeO3 samples（x = 0.1, 0.2 and 0.3） were synthesized by the conventional solid-state reaction method using nano-powders of Bi2O3, Fe2O3, and BaCO3. Thereafter, field emission scanning electron microscope and X-ray diffraction（XRD） techniques were used to examine the structure and phase of the samples. Phase analysis by XRD indicated that the single-phase perovskite structure was formed with possible increment in lattice parameter with increasing Ba doping. Complex permeability（u＇iand u＇＇i） measured using impedance analyzer confirmed the increase in magnetic property with increasing Ba doping. Finally, dielectric constant（k） was analyzed as a function of temperature at different frequencies. Dielectric constant as high as 2900 was attained in this research for Bi0.8Ba0.2FeO3 sample due to reduction in leakage current at this composition.

Optimization of Ni_(0.95-x)Zn_(x)Co_(0.05)Fe_(1.90)Mn_(0.02)O_(4) ceramics with promising magneto-dielectric properties for VHF antenna miniaturization

Magnetic,dielectric and DC conductive properties of Ni_(0.95-x)Zn_(x)Co_(0.05)Fe_(1.90)Mn_(0.02)O_(4)(with x=0-0.20 at an interval of 0.05)ferrite ceramics were studied,in order to develop magneto-dielectric materials with almost equal values of relative permeability and permittivity,for the miniaturization of HF(3-30 MHz)and VHF(30-90MHz and 100-300 MHz)antennas.The ferrite ceramics were prepared by using the conventional two-step sintering process.The real part of relative permeability is increased almost linearly with increasing concentration of Zn,while that of relative permittivity keeps nearly unchanged.It is found that promising magneto-dielectric materials,with close values of real permeability and permittivity over 30-90 MHz(VHF),can be obtained for the samples at Zn concentrations between x=0.05 and x=0.10.

Citric Acid-Enhanced Electroremediation of Toxic Metal-Contaminated Dredged Sediments： Effect of Open/Closed Orifice Condition, Electric Potential and Surfactant

Citric acid(CA), a widely used eco-friendly electrolyte, can be employed as an agent for enhancing toxic metal(TM) removal from contaminated dredged sediment using electrokinetic(EK) technology. In this study, dredged harbor sediments co-contaminated by TMs were subjected to enhanced EK treatment using a mixture of chelating agent(CA) and surfactant as an additive in the processing fluids. Several control conditions that may influence the efficiency of TM removal were tested, including open/closed sediment chamber orifices, electric potential gradients(0.5, 1.0, and 1.5 V cm^(-1)), and electrolyte surfactant. Tween 20(4 mmol L-1) was used as a surfactant within the electrolyte to investigate the extent of TM removal in sediment with high organic matter content. The results showed that an open orifice led to a greater electro-osmotic flow(EOF) with moderate TM removal. In contrast, a closed orifice with a nonionic surfactant electrolyte allowed the highest removal of TMs from the matrix. Moreover, increasing the electric potential gradient led to a higher EOF under the open orifice condition, but no significant increase in TM removal was observed owing to a higher accumulation of TMs in the middle of the matrix, caused by the opposite direction of EOF and electro-migration of metal-citrate complexes.