Synthesis and characterization of magnetic and microwave absorbing properties in polycrystalline cobalt zinc ferrite (Co<Subscript>0.5</Subscript>Zn<Subscript>0.5</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript>) composite

In this research work, magnetic and microwave absorption loss and other response characteristics in cobalt zinc ferrite composite has been studied. Cobalt zinc ferrite with the composition of Co_0.5Zn_0.5Fe₂O₄ was prepared via high energy ball milling followed by sintering. Phase characteristics of the as-prepared sample by using XRD analysis shows evidently that a high crystalline ferrite has been formed with the assists of thermal energy by sintering at 1250 °C which subsequently changes the magnetic properties of the ferrite. A high magnetic permeability and losses was obtained from ferrite with zinc content. Zn substitution into cobalt ferrite has altered the cation distribution between A and B sites in spinel ferrite which contributed to higher magnetic properties. Specifically, Co_0.5Zn_0.5Fe₂O₄ provides electromagnetic wave absorption characteristics. It was found that cobalt zinc ferrite sample is highly potential for microwave absorber which showed the highest reflection loss (RL) value of ??24.5 dB at 8.6 GHz. This material can potentially minimize EMI interferences in the measured frequency range, and was therefore used as fillers in the prepared composite that is applied for microwave absorbing material.     

Piezoelectric and magnetic properties of PZT-(Ni<Subscript>0.284</Subscript>Zn<Subscript>0.549</Subscript>Cu<Subscript>0.183</Subscript>)Fe<Subscript>1.984</Subscript>O<Subscript>4</Subscript> composites

The piezoelectric/piezomagnetic composite, PZT/Ni_0.284Zn_0.549Cu_0.183Fe_1.984O₄, was fabricated by the mixed oxide method. The phase assemblage, piezoelectric strain constant and saturation magnetization were investigated. The results indicate that the PZT phase is compatible with Ni_0.284Zn_0.549Cu_0.183Fe_1.984O₄ phase, and dense diphasic ceramic composites were obtained. It is found that piezoelectric strain constant decreases exponentially as the amount of doped piezomagnetic materials in the composite increases. Correspondingly, saturation magnetization of the composite also decreases with the increasing weight fraction of piezoelectric materials. Three reasons cause the results. First, the grain growth of piezomagnetic phase at the co-sintering temperature reduces grain size and continuity of the piezoelectric phase. Second, the pore size and porosity in composite increase dramatically with increasing amount of piezomagnetic phase. Third, the low resistivity of the composite prevents the poling process and reduces the piezoelectric strain constant. The tailoring of microstructure to achieve a high performance piezoelectric/piezomagnetic composite is proposed based on the analysis.     

Dielectric,humidity behavior and conductivity mechanism of Mn<Subscript>0.2</Subscript>Ni<Subscript>0.3</Subscript>Zn<Subscript>0.5</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> ferrite prepared by co-precipitation method

Mn–Ni–Zn ferrite with the chemical formula of Mn_0.2Ni_0.3Zn_0.5Fe₂O₄ was prepared by co-precipitation method. The X-ray diffraction (XRD) results show that the prepared sample crystallizes in the cubic spinel structure with the space group of Fm3m. The morphological analysis of the sample was investigated by scanning electron microscopy (SEM). The dielectric properties of Mn_0.2Ni_0.3Zn_0.5Fe₂O₄ ferrite were studied in a frequency range from 20 Hz to 10 MHz and at a temperature range from 293 to 733 K. The dielectric constant decreases with the increasing frequency for all the temperature values chosen. The AC conductivity mechanism was found the small polaron type of conductivity, and in addition to that, the DC conductivity can be explained by Arrhenius type conductivity. According to the dielectric results, relaxation process fits Cole–Cole model. Finally, the effect of the relative humidity upon the impedance of the sample was discussed for a frequency range between 20 Hz and 10 MHz. It is found that the impedance values decrease almost linearly with the increasing % RH (relative humidity) values at low frequencies, while the impedance of the sample is independent of % RH at high frequencies.     

Structural,dielectric, ac conductivity and electromagnetic shielding properties of polyaniline/Ni<Subscript>0.5</Subscript>Zn<Subscript>0.5</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> composites

A conducting polymer, polyaniline (PANI)/Ni_0.5Zn_0.5Fe₂O₄ composites with high dielectric absorbing properties and electromagnetic shielding effectiveness at low frequencies were successfully synthesized through a simple in situ emulsion polymerization. PANI was doped with hydrochloric acid to improve its electrical properties and interactions with ferrite particles. PANI/Ni_0.5Zn_0.5Fe₂O₄ composites were characterized by X-ray diffraction analysis, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy and thermal gravimetric analysis. Frequency dependence of dielectric and ac conductivity (σ_ac) studies have been undertaken on the PANI/Ni_0.5Zn_0.5Fe₂O₄ composites in the frequency range 50 Hz–5 MHz. The electrical conduction mechanism in the PANI/Ni_0.5Zn_0.5Fe₂O₄ is found to be in accordance with the electron hopping model. Further, frequency dependence of electromagnetic interference (EMI) shielding effectiveness (SE) is studied. The EMI shielding effectiveness is found to decrease with an increase in the frequency. The maximum value 55.14 dB of SE at 50 Hz was obtained at room temperature for PANI/Ni_0.5Zn_0.5Fe₂O₄ composites in the 50 Hz–5 MHz frequency range. PANI/Ni_0.5Zn_0.5Fe₂O₄ composites were demonstrated as a promising functional material for the absorbing of electromagnetic waves at low frequencies because of a large amount of dipole polarizations in the polymer backbone and at the interfaces of the Ni–Zn ferrite particles and PANI matrix.     

Local amorphization of atomic structure in Mg<Subscript>0.54</Subscript>Zn<Subscript>0.46</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> ferrites

The structure of Mg_0.54Zn_0.46Fe₂O₄ ferrites has been studied using x-ray diffraction techniques. It is established that high-temperature annealing (T = 1280°C, τ = 0.5–8.0 h) leads to a change in the crystal structure of samples, which is accompanied by their local amorphization.     

Fast microwave synthesis of Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> and Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/Ag magnetic nanoparticles using Fe<Superscript>2+</Superscript> as precursor

A simple and quick microwave method to prepare high performance magnetite nanoparticles (Fe₃O₄ NPs) directly from Fe has been developed. The as-prepared Fe₃O₄ NPs product was fully characterized by X-ray diffraction, transmission electron microscopy and scanning electron microscopy. The results show that the as-prepared Fe₃O₄ NPs are quite monodisperse with an average core size of 80 × 5 nm. The microwave synthesis technique can be easily modified to prepare Fe₃O₄/Ag NPs and these NPs possess good magnetic properties. The formation mechanisms of the NPs are also discussed. Our proposed synthesis procedure is quick and simple, and shows potential for large-scale production and applications for catalysis and biomedical/biological uses.     

Synthesis and microwave absorption properties of sandwich-type CNTs/Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>/RGO composite with Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> as a bridge

A novel sandwich-type CNTs/Fe₃O₄/RGO composite with Fe₃O₄ as a bridge was successfully prepared through a simple solvent-thermal and ultrasonic method. The structure and morphology of the composite have been characterized by Fourier-transform infrared spectroscopy, X-ray diffraction and scanning electron microscopy. This new structure can effectively prevent the agglomeration of GO and the combination of CNTs/Fe₃O₄ and RGO shows a strong reflection loss (R_L) (?50 dB) at 8.7 GHz with absorber thickness of 2.5 mm. Moreover, compared with CNTs/Fe₃O₄/GO composite, it is found that the thermal treating process is beneficial to enhance the microwave absorption properties, which may be attributed to high conductivity of RGO. On this basis, the microwave absorbing mechanism is systematically discussed. All the data show that the CNTs/Fe₃O₄/RGO composite exhibits excellent microwave absorption properties with light density and is expected to have potential applications in microwave absorption.     

Synthesis of water-based Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> magnetic nanoparticles,stabilized by oleic acid and mannitol

Water-based Fe₃O₄ magnetic nanoparticles were synthesized and studied, stabilized by oleic acid and mannitol. Nanoparticles were prepared by dropwise introduction of aqueous salt solution of iron (II) and (III) into aqueous ammonia. The double salts of iron were taken as a source of iron ions: ferric alum and Mohr’s salt.     

Synthesis by the solution combustion process and magnetic properties of iron oxide (Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> and α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>) particles

This article describes the solution combustion synthesis technique as applicable to iron oxide powder production using urea as fuel and ferric nitrate as an oxidizer. It focuses on the thermodynamic modeling of the combustion reaction under different fuel-to-oxidant ratios. X-ray diffraction showed magnetite (Fe₃O₄) and hematite (α-Fe₂O₃) phase formations for the as-synthesized powders. The smallest crystallite size was obtained by stoichiometric chemical reaction. The magnetic properties of the samples are also carefully discussed as superparamagnetic behavior.     

Dielectric and magnetic properties of Ca(Zn<Subscript>1/3</Subscript>Nb<Subscript>2/3</Subscript>)O<Subscript>3</Subscript>/NiZn ferrite composites

Dense Ca(Zn_1/3Nb_2/3)O₃/NiZn ferrite composites with homogeneously fine microstructures were prepared through conventional solid-state method. The powder XRD patterns confirm the coexistence of the two phases. The dielectric properties in the low frequency range (100 Hz–1 MHz) follow the rule of Maxwell–Wagner interfacial polarization. The dielectric and magnetic properties in the high frequency range (10 MHz–1 GHz) are also reported. The results show that this kind of magnetic–dielectric composites could be used in high-frequency communications for the capacitor-inductor integrating devices such as electromagnetic interference filters and antennas.     

Electrical properties of Ni<Subscript>0.93</Subscript>Co<Subscript>0.02</Subscript>Mn<Subscript>0.05</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> + BaTiO<Subscript>3</Subscript> ME composites

Polycrystalline samples of mixed composites of Ni_0.93Co_0.02Mn_0.05Fe₂O₄ + BaTiO₃ were prepared by conventional double sintering ceramic method. The phase analysis was carried out by using X-ray diffraction technique. Variation of dc resistivity and thermo emf was studied as a function of temperature. AC conductivity (σ_ac) was investigated in the frequency range 100 Hz–1 MHz. The loss tangent (tan δ) measurements conclude that the conduction mechanism in these samples is due to small polaron hopping. The magnetoelectric conversion factor, i.e. dc(ME) _H was studied as a function of intensity of magnetic field and the maximum value 407 μV/cm/Oe was observed at a field of 0.8 kOe in a composite with 85% BaTiO₃ and 15% Ni_0.93Co_0.02Mn_0.05Fe₂O₄ phase.     

Effects of alkaline-earth dopants on structural,optical and magnetic properties of Bi<Subscript>2</Subscript>Fe<Subscript>4</Subscript>O<Subscript>9</Subscript> powders

The pure Bi₂Fe₄O₉ and Bi_{2 (1?x)} A_2xFe₄O₉ (A?=?Ca, Ba, x?=?0.03) powders are synthesized via a modified solid-state reaction method to study the effects of alkaline-earth metal ions doping on crystal structural, optical and magnetic properties. Both X-ray diffraction and Raman spectroscopy data reveal that all the powders are Mullite-type Bi₂Fe₄O₉ orthorhombic single phase without any impurities. Much greater structural distortion in Bi_1.94Ba_0.06Fe₄O₉ than that of Bi_1.94Ca_0.06Fe₄O₉ is observed. The chemical compositions of Ba²⁺ and Ca²⁺ doped powders have been investigated with energy dispersive X-ray spectroscopy (EDS). X-ray photoelectron spectroscopy results indicate that oxygen vacancies could be found in all doped powders. The ratio of Fe²⁺ in the total Fe ions is almost unchanged by Ca doping and increases a little with Ba substitution. Compared with that of pure Bi₂Fe₄O_9, the band gap values decrease slightly in Bi_1.94Ca_0.06Fe₄O₉ but drop dramatically in Bi_1.94Ba_0.06Fe₄O₉. A clear and obvious ferromagnetic behavior is found in Bi_1.94Ba_0.06Fe₄O₉ at 10 K. However, Bi_1.94Ca_0.06Fe₄O₉ shows a weak ferromagnetism with enhanced magnetization and Bi₂Fe₄O₉ exhibits antiferromagnetism with a linear M–H relationship. The varied bandgap and magnetization resulting from the alkaline-earth metal ionic species are discussed in terms of structural distortion due to the ionic radius size effect.     

Synthesis,structure, and thermal expansion of M<Subscript>2</Subscript>Fe<Subscript>2</Subscript>Ti<Subscript>6</Subscript>O<Subscript>16</Subscript> and MFeTiO<Subscript>4</Subscript> compounds

Compounds that crystallize in four structure types in M₂O-Fe₂O₃-TiO₂ systems have been prepared by solid-state reactions. The M₂Fe₂Ti₆O₁₆ (M = Rb, Cs) compounds have been prepared for the first time. The thermal expansion coefficients of the MFeTiO₄ (M = Li, Na) and M₂Fe₂Ti₆O₁₆ (M = Na, K, Rb, Cs) compounds have been determined by high-temperature X-ray diffraction.     

Synthesis and excellent microwave absorption property of polyaniline nanorods coated Li<Subscript>0.435</Subscript>Zn<Subscript>0.195</Subscript>Fe<Subscript>2.37</Subscript>O<Subscript>4</Subscript> nanocomposites

In this work, Li_0.435Zn_0.195Fe_2.37O₄ (LZFO) was firstly prepared by the sol–gel process, and then core–shell polyaniline (PANI) nanorods/LZFO composites were successfully synthesized by interfacial polymerization. The structures and morphologies of samples were characterized by means of X-ray diffraction, Fourier transform infrared spectra, and scanning electron microscopy. The average size of the pure ferrites was about 0.75 μm and the size distribution was 0.3–1.0 μm. The results indicated that the composites with different morphologies and structures resulted in different electromagnetic properties. The electromagnetic absorption test demonstrated that the PANI nanorods/LZFO possessed the best absorption property. The value of the minimum reflection loss was ?51.1 dB at 9.86 GHz, and the absorption bandwidth exceeding ?10 dB was 2.3 GHz (from 3.7 to 6 GHz) and 2 GHz (from 15.7 to 17.7 GHz). The excellent electromagnetic wave absorption properties of the nanocomposites were attributed to the improved impedance matching and the enhanced interfacial effects.     

Microstructure and magnetic properties of Ni<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Zn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> synthesized by combustion reaction

An investigation was made of samples having a chemical formula of Ni_1−x Zn _x Fe₂O₄, where x = 0.3, 0.5 and 0.7. The samples were prepared by the reaction combustion synthesis method and sintered at 1,200 °C/2 h in a static air atmosphere. The influence of the Zn concentration on the relative density, microstructure and magnetic properties of the samples was studied. X-ray diffraction, scanning electron microscopy and magnetic hysteresis loop tracer were used to analyze the compositions. The samples were found to have a spinel cubic structure, sintered density of 92.9%–98.8% of the corresponding X-ray density, homogeneous microstructure with grain size ranging from 1.37 to 3.36 μm, maximum flux density of 0.16–0.35 T, field coercivity ranging from 17 to 168 A/m, and loss hysteresis of 1.5–105 W/kg. Increased grain growth, with fine pores inside the grains, was found to occur as the Zn concentration increased. The overall findings are discussed here in light of the existing understanding of these systems.     

Effect of nickel on the structural and magnetic properties of nano structured CoZnFe<Subscript>2</Subscript>O<Subscript>4</Subscript>

Nano particles of Co_(0.5–x)Ni_xZn_0.5Fe₂O₄ (x = 0–0.3) were synthesized by chemical coprecipitation method. Powder X-ray diffraction pattern confirms the formation of spinel phase for all the prepared samples. The lattice parameters were calculated from powder X-ray diffraction data and the result reveals that the values are less than that of bulk values. The saturation magnetization decrease for the concentration x = 0.1 and increases for all the other concentration. Further, the hysteresis loop for the concentration x = 0 and 0.1 shows that there is no coercivity and remanance at 300 K and hence the samples behaves as superparamagnetic at 300 K. The field-cooled (FC) and zero-field-cooled (ZFC) curve for the concentration x = 0 and 0.1 separates at 150 and 167 K respectively hence the prepared samples behaves as superparamagnetic at room temperature.     

Dielectric and ferromagnetic properties of BaTiO<Subscript>3</Subscript>/Ni<Subscript>0.93</Subscript>Co<Subscript>0.02</Subscript>Cu<Subscript>0.05</Subscript>Fe<Subscript>2</Subscript>O<Subscript>4</Subscript> composites

xBaTiO₃ + (1 − x)Ni_0.93Co_0.02Cu_0.05Fe₂O₄ (x = 0.5, 0.6, 0.7, 0.8) composites with ferroelectric–ferromagnetic characteristics were synthesized by the ceramic sintering technique. The presence of constituent phases in the composites was confirmed by X-ray diffraction studies. The average grain size was calculated by using a scanning electron micrograph. The dielectric characteristics were studied in the 100 kHz to 15 MHz. The dielectric constant changed higher with ferroelectric content increasing; and it was constant in this frequency range. The relation of dielectric constant with temperature was researched at 1, 10, 100 kHz. The Curie temperature would be higher with frequency increasing. The hysteresis behavior was studied to understand the magnetic properties such as saturation magnetization (M _s). The composites were a typical soft magnetic character with low coercive force. Both the ferroelectric and ferromagnetic phases preserve their basic properties in the bulk composite, thus these composites are good candidates as magnetoelectric materials.     

The production and structure of submicrometer Eu<Subscript>0.75</Subscript>Fe<Subscript>0.25</Subscript>O films on InSb,Si, and GaAs substrates

The conditions for fabrication and the crystal structure of the up-to-350-nm-thick Eu_0.75Fe_0.25O layers formed on InSb, Si, and GaAs substrates are studied. For the first time, 100–200 nm films with morphological surface inhomogeneities not exceeding 10 nm in size are produced by flash evaporation of targets close in composition to Eu_0.75Fe_0.25O onto InSb(001) substrates. The films exhibit ferromagnetic properties in combination with semiconductor properties at room temperatures.     

Synthesis and applications of fluorescent-magnetic-bifunctional dansylated Fe<Subscript>3</Subscript>O<Subscript>4</Subscript>@SiO<Subscript>2</Subscript> nanoparticles

Bifunctional magnetic-luminescent dansylated Fe₃O₄@SiO₂ (Fe₃O₄@SiO₂-DNS) nanoparticles were fabricated by the nucleophilic substitution of dansyl chloride with primary amines of aminosilane-modified Fe₃O₄@SiO₂ core–shell nanostructures. The morphology and properties of the resultant Fe₃O₄@SiO₂-DNS nanoparticles were investigated by transmission electron microscopy, FT–IR spectra, UV–vis spectra, photoluminescence spectra, and vibrating sample magnetometry. The Fe₃O₄@SiO₂-DNS nanocomposites exhibit superparamagnetic behavior at room temperature, and can emit strong green light under the excitation of UV light. They show very low cytotoxicity against HeLa cells and negligible hemolysis activity. The T ₂ relaxivity of Fe₃O₄@SiO₂-DNS in water was determined to be 114.6 Fe mM⁻¹ s⁻¹. Magnetic resonance (MR) imaging analysis coupled with confocal microscopy shows that Fe₃O₄@SiO₂-DNS can be uptaken by the cancer cells effectively. All these positive attributes make Fe₃O₄@SiO₂-DNS a promising candidate for both MR and fluorescent imaging applications.     

Characterization and electrical properties of semiconducting Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>-K<Subscript>2</Subscript>B<Subscript>4</Subscript>O<Subscript>7</Subscript> glasses

Semiconducting glasses of the Fe₂O₃-Bi₂O₃-K₂B₄O₇ system were prepared by the press-quenching method and their dc conductivity in the temperature range 223–393 K was measured. The glass transition temperature values (T_g) of the present glasses were larger than those of tellurite glasses. This indicates a higher thermal stability of the glass in the present system. The density for these glasses was consistent with the ionic size, atomic weight and amount of different elements in the glasses. Mössbauer results revealed that the relative fraction of Fe increases with increasing Fe₂O₃ content. Electrical conductivity showed a similar composition dependency as the fraction of Fe. The glasses had conductivities ranging from 10 to 10 Scm at temperatures from 223 to 393 K. Electrical conduction of the glasses was confirmed to be due to non-adiabatic small polaron hopping and the conduction was primarily determined by hopping carrier mobility.