Ferrite Crystals Research Articles

Microstructure and enhanced electromagnetic wave absorbing performance of Zn0.6Ni0.3Cu0.1Fe2O4 ferrite glass-ceramic

Here we introduce a controllable route for the efficient synthesis of Zn0.6Ni0.3Cu0.1Fe2O4 ferrite glass-ceramic with enhanced electromagnetic wave (EMW) absorbing performance. By adding a certain amount of Zn, Ni, Cu and Fe oxides into the SiO2–Al2O3–B2O3–CaO-R2O glass system, the microstructure of three-dimensional dendritic ferrites combined with amorphous SiO2-rich phase is constructed through a high-temperature melt and quenching route. The good EMW absorption performance is attributed to the unique combination of amorphous glass and spinel ferrite, which improves the impedance matching of the material and absorbs EMW by the dielectric loss and magnetic loss. Moreover, the dendritic ferrite crystal phase is compounded with the SiO2-rich amorphous phase to form grain boundaries and crystal-amorphous interfaces, which enhances the interfacial polarization and builds multiple transmission-absorption mechanisms. The results show that the reflection loss peak value of the glass-ceramics containing 60 wt% Zn0.6Ni0.3Cu0.1Fe2O4 spinel is −42.16 dB with the sample thickness of 2 mm, and the effective absorption band range (reflection loss ≤ -10 dB) is 3.76 GHz (13.6–17.36 GHz) at 1.5 mm. This approach presents a scalable and low-cost solution that may be applied to the design of high-efficiency EMW consumption components in the future.

Structural and Magnetoelectrical Properties of MFe2O4 (M = Co, Ni, Cu, Mg, and Zn) Ferrospinels Synthesized via an Egg-White Biotemplate.

Nanocrystalline metal ferrites (MFe2O4, M = Co, Ni, Cu, Mg, and Zn) were successfully synthesized via autocombustion synthesis using egg white. X-ray diffraction (XRD) measurements revealed the crystallization of the entire ferrites either in the tetragonal structure, such as in the case of CuFe2O4, or cubic spinels such as in other studied ferrites. The Fourier transform infrared spectral study revealed the characteristic vibration bands of ferrites. Compared to other synthesis methods, the observed variation in the obtained structural parameters could be due to the different cation distribution of the prepared ferrites. In agreement with XRD measurements, the transmission electron microscopy images showed agglomerated particles with cubic morphology for all ferrites. On the other hand, CuFe2O4 showed tetragonal morphology. The magnetization values were found to vary with the type of the metal ion, and CoFe2O4 showed the highest one (42.8 emu/g). Generally, the lower magnetization values obtained than those reported in the literature for all studied ferrites could be attributed to the smaller particle sizes or the cation redistribution. The obtained coercivity values are observed to be higher than their related values in the literature, exhibiting the impact of the present synthesis route. Ac-conductivity as a function of temperature and frequency indicated semiconducting properties with the observed change in the conduction mechanism by increasing the temperature. The obtained low dielectric constant values could suggest using the entire ferrites in high-frequency applications such as microwave devices.

Effect of strontium substitution in cobalt ferrite: Structural and optical studies

A set of strontium (Sr)-doped cobalt (Co) nanoferrites Co1-xSrxFe2O4 (x = 0.1 and 0.2) was synthesized using a sol-gel combustion method. The phase, nanocrystallinity, and optical properties of as-prepared and annealed samples were investigated. The average crystallite sizes obtained were 36, 40, and 30 nm for the nanoferrites with lattice parameters of 8.25, 8.30, and 8.30 Å, respectively. Raman spectroscopy confirmed the spinel structure of the ferrite crystals. The existence of cations at the octahedral and tetrahedral sites in the nanoparticles was also confirmed by X-ray photoelectron spectroscopy. Direct bandgap energy values of 1.29, 1.32, and 1.35 eV were determined and an applied temperature of 680 °C ensured the complete decomposition of precursors. The correlation between the Sr substitution in Co ferrite and the structural and optical changes is discussed.

Preparation of copper ferrite by sol–gel method and the synergistic catalytic for the thermal decomposition of ammonium perchlorate

In the present work, copper ferrite was prepared by a simple and mild sol–gel method followed by low-temperature calcination, and characterized by various analytical techniques. The X-ray diffraction (XRD) analysis suggests that the copper ferrite with the spinel-type ferrite crystal forms have been successfully prepared. More crystal defects are observed in copper ferrite crystals than in the pure iron oxide and copper oxide crystals. The scanning electron microscopy (SEM) and nitrogen adsorption–desorption analyses reveal that the prepared copper ferrites are mesoporous structures with large specific surface areas and the specific surface area increases with the increase of Fe content. The effects of the structure of copper ferrite on its catalytic activity for the thermal decomposition of ammonium perchlorate (AP) and the catalytic mechanism were investigated and explored based on the thermogravimetric analysis of the decomposition process. It is found that the copper ferrites prepared at the molar ratios of Cu/Fe of 1/2 and 1/4 exhibit the best catalytic activities for the thermal decomposition of AP. The synergistic catalytic mechanism of Cu–Fe–O is proposed based on the electron transfer and proton transfer theories for the thermal decomposition of AP.

Enhanced calcination temperatures of Zn0.6Ni0.2Cu0.2Fe2O4 on thermal, microstructures and magnetic properties using Co-precipitation method

Synthesis of Zn0.6Ni0.2Cu0.2Fe2O4 has been successfully using the co-precipitation method at a calcination temperatures of 300 °C, 400 °C and 500 °C. Thermal properties, microstructures, and magnetic properties were obtained from the characterization of Thermogravimetric Analysis/Differential Scanning Calorimetry (TGA/DSC), X-ray Diffraction (XRD), Field Emission - Scanning Electron Microscope (FE-SEM). Vibrating Sample Magnetometer (VSM) used for analyses magnetic properties of ZnCuNi Ferrite. TGA/DSC results that the reduction of weight is 6.72% in range at 95 °C–100 °C and endotermic process occurs at temperatures below 100 °C. XRD results that confirmed that the higher calcination temperature that affects the growth of ZnNiCu spinel ferrite crystals and the increase in the crystallite size are found within 17.75–20.15 nm. FE-SEM conducted that effect increase calcination temperature reduced particle size, faster diffusion of metal oxidation, and increasing the rate at which the cubic particles crystallize in spinel ferrite. The optimum conditions properties obtained for Zn0.6Ni0.2Cu0.2Fe2O4 at a calcination temperature of 500 °C, Ms = 31.79 emu/g, Mr = 12.06 emu/g, Hc = 331.06 Oe, respectively.

The wide-angle broadband absorption and polarization separation in the one-dimensional magnetized ferrite photonic crystals arranged by the Dodecanacci sequence under the transverse magnetization configuration

Utilizing the transfer matrix method, a multifunctional infrared device possessing the properties of the wide-angle broadband absorption and the polarization separation based on the one-dimensional (1-D) magnetized ferrite photonic crystals (MFPCs) arranged by the Dodecanacci sequence is designed theoretically under the modulation of the external magnetic field. The magneto-optical effect generated in the proposed MFPCs gives birth to the ultra-broadband absorption regions under the transverse electric (TE) mode, one runs at 16.22 THz –30.89 THz and the other covers at 33.52 THz–70.00 THz. The mechanism of the wide-angle (at most 80.89° for TE mode) absorption is analyzed by the interference cancellation condition. Moreover, owing to the different effective permeabilities of the MFPCs under the two polarization modes, the propagation behaviors of the electromagnetic (EM) wave are diverse which present the absorption features under the TE mode and show the transmission properties under the transverse magnetic (TM) mode in the structure. Compared with the periodic and Thue-Morse structures, the complex symmetry of the Dodecanacci sequence makes the absorption features of the MFPCs superior to that of the former. Besides, the influences of the magnetic field intensity and the dielectrics’ thicknesses on the angle-insensitive absorption and polarization separation characteristics are discussed explicitly. This research provides meaningful guidance for the modulation and absorption of the infrared light wave and the design of the multifunctional magnetically tunable optoelectric device.

On the disperse acicular ferrite formation in the structure of cold-resistant joints under temperatures up to –70°С in MMA welding of 10KhSND steel. Part 1

The article presents an analysis of the metallurgical techniques that provide high quality electrodes for manual arc welding of low-carbon low-alloyed cold-resistant steels. It is shown that it is possible to improve technological and operational properties of welded joints at very low climatic temperatures up to –70°C implementing micro-alloying of the weld metal with nitrogen, titanium, cerium oxide and diamond nanopowder produced by detonation synthesis. The composition introduced into the electrode coating modifier mixture is identified. The cumulative effect of its components on the weld impact strength under temperature testing within the range from –20 up to –70°C was established. The matrix of the weld metal is composed mainly of disperse acicular ferrite, hardened by nanoparticles allegedly nitrides and carbonitrides of titanium and aluminum. It is shown that the centers for the crystallization of acicular ferrite are micro-sized non-metallic inclusions formed on ultrafine titanium nitrides. It was revealed that the toughness of the weld metal at low climatic temperatures is higher than toughness of joints welded by massively imported Japanese KOBELCO electrodes LB-52U. The results of the study make it possible to increase the cold resistance of welded structures for petrochemical plants and other facilities located in the Extreme North of the Russian Federation.Part 2 of the article will be devoted to the study of the welding and technological properties of coated electrodes.

Synthesis and Characterization of Core–Shell Magnetic Nanoparticles NiFe2O4@Au

In this study, NiFe2O4@Au core–shell nanoparticles were prepared by the direct reduction of gold on the magnetic surface using amino acid methionine as a reducer and a stabilizing agent simultaneously. The obtained nanoparticles after three steps of gold deposition had an average size of about 120 nm. The analysis of particles was performed by X-ray diffraction, transmission electron microscopy, X-ray photoelectron spectroscopy, and UV-Vis spectroscopy techniques. The results indicate successful synthesis of core–shell particles with the magnetic core, which consists of a few agglomerated nickel ferrite crystals with an average size 25.2 ± 2.0 nm, and the thick gold shell consists of fused Au0 nanoparticles (NPs). Magnetic properties of the obtained nanoparticles were examined with magnetic circular dichroism. It was shown that the magnetic behavior of NiFe2O4@Au NPs is typical for superparamagnetic NPs and corresponds to that for NiFe2O4 NPs without a gold shell. The results indicate the successful synthesis of core–shell particles with the magnetic nickel ferrite core and thick gold shell, and open the potential for the application of the investigated hybrid nanoparticles in hyperthermia, targeted drug delivery, magnetic resonance imaging, or cell separation. The developed synthesis strategy can be extended to other metal ferrites and iron oxides.

Time resolved fluorescence and Raman properties, and zeta potential of zinc ferrite nanoparticles dispersed nematic liquid crystal 4′-heptyl-4-biphenylcarbonitrile (7CB)

The present work reports the results on the time resolved fluorescence, Raman properties and Zeta potential of pristine and zinc ferrite nanoparticles (ZnFe2O4 NPs) dispersed nematic liquid crystal, 4′-heptyl-4-biphenylcarbonitrile (7CB). It has been observed that the dispersion of ZnFe2O4 NPs into nematic 7CB matrix induces quenching of photoluminescence, reduces the Ultra-Violet-Visible (UV‐–Vis) absorbance of pure nematic 7CB at lower wavelength, and increases the numerical value of zeta potential. The maxima in absorbance curve occur at the same wavelength but the absorbance is decreased. The emission peaks in pure nematic sample occur at 376 nm and 383 nm. Variations in the Raman intensity profile are observed for different orientations. This variation is more noticeable for the CC bond in aromatic ring and the C ≡ N group both located along the long axis of the nematic liquid crystal (NLCs) system.

Structural modifications in Co–Zn nanoferrites by Gd substitution triggering to dielectric and gas sensing applications

The structural modifications in Co–Zn ferrites due to the substitution of Gd3+ ions and their credible use as low loss dielectrics and H2S gas sensors are reported in the present study. The structural modifications lead to the enhancement in physical properties of the ferrites making it suitable for the applications. The nanocrystals of Co0·7Zn0·3Fe2-xGdxO4 (0 ≤ x ≤ 0.1, Δx = 0.025) were obtained using self-ignited citrate sol-gel route of synthesis. The X-ray diffractograms of the ferrites were refined by Rietveld method using the full-proof pdf software. The refinement asserts the creation of mono phase spinel ferrite crystals. The morphology of ferrite crystals analyzed from scanning electron microscopy (SEM) profiles depict that the ferrites exhibit the porous nature. The transmission electron microscopy (TEM) images confirms the nanocrystalline nature of the ferrites with an average dimension of 25 nm and high resolution TEM (HRTEM) confirms the spinel phase created within the ferrites. The frequency variation of dielectric parameters was analyzed to study the relaxation phenomenon in ferrites. The values of dielectric constant, dielectric loss and loss tangent were reported to decline with frequency and the Gd3+composition (x). The a.c. electrical conductivity increases with frequency and decreases with composition ‘x’. The room temperature gas sensing response of the ferrite for the hazardous H2S gas was much higher than that for LPG, SO2, NO2 and H2 gases. The ferrite sample with x = 0.025 exhibits a better sensor performance for H2S gas with small recovery and response time. The nanocrystalline nature, porosity and morphology of the ferrites bear control over response and other parameters.

DOMAIN STRUCTURE AND SOME PROPERTIES OF RARE-EARTH GRANITE FERRITES

The crystals of rare-earth garnet ferrites have a complex domain structure, the form of which substantially depends on the crystallographic orientation of the under study sample. Due to the cubic symmetry of rare-earth garnet ferrites, 70, 110, and 180-degree domains can exist in them, and depending on the crystallographic orientation of the sample, the spontaneous magnetization vector in the realized domain configuration can lie in the plane of the sample (“Cotton” domains) perpendicular to the plane of the sample ("Faraday" domains), and make up a certain angle with its plane. According to known data, in all cases, the boundaries between neighboring domains in rare-earth garnet ferrites are the domain walls of the Bloch type

Weld structure of low-carbon structural steel formed by ultrasonic-assisted laser welding

The present study is aimed to examine the structure of a welded joint of low-carbon structural steel A 516–55 formed by melting under laser irradiation and by subsequent melt solidification. The main disadvantage of the weld structure in this steel is the formation of plate- and needle-like Widmanstätten ferrite in the conditions of ultra-fast heating and cooling which adversely affects the strength properties of the welded joints. It is shown that the application of ultrasonic vibrations during welding changes the melt solidification conditions and positively affects the dispersion of dendrites and growing Widmanstätten ferrite crystals.

Formation mechanism of zinc ferrite in high-temperature roasting of zinc oxide and ferric oxide

The formation mechanism of zinc ferrite during the heat treatment of zinc oxide and ferric oxide was investigated. It is revealed in the kinetic study that the formation of zinc ferrite is an endothermic reaction with an apparent activation energy Ea that increases from 9.76 kJ mol−1 to 290.70 kJ mol−1. This variation of Ea indicates that the reaction between ZnO and Fe2O3 is a multistep reaction, which could be described by the D3 (3D Jander Equation) - An (n-dimension Avrami-Erofeev Equation) model. The first step is the diffusion of the reactant, corresponding to the stage when the Ea is low. As the reaction proceeds, the rate-determining process switches to the crystallization of zinc ferrite, which is reflected by a simultaneous increase in the XRD peak height and Ea. The results of first-princeples calculations show that zinc oxide preferentially diffuses to the iron oxide matrix, and the inverse process causes an increase in the system energy. These results provide great insight into the kinetic basis for understanding the formation of spinel ferrites via a high-temperature solid-state reaction.

Potassium Ferrite as Heterogeneous Photo-Fenton Catalyst for Highly Efficient Dye Degradation

In this work, hexagon-shaped potassium ferrite (K2Fe4O7) crystals with different sizes were prepared using the hydrothermal method. The crystals showed a narrow band gap of 1.44 eV, revealed by UV-visible diffuse reflectance spectroscopy, and was thus used as a heterogeneous Fenton catalyst to degrade methylene blue (MB) and crystal violet (CV) in the presence of green oxidant H2O2 under visible-light irradiation. Among the investigated crystals, the as-prepared one with an average size of 20 µm (KFO-20) exhibited better photocatalytic activity due to its high surface area. When it was used as a photo-Fenton catalyst, 100% MB and 92% CV were degraded within 35 min. Moreover, the catalyst maintained high photocatalytic activity and was stable after four continuous cycles. The trapping experiments showed that the active hydroxyl radical (·OH) was dominant in the photo-Fenton reaction. Therefore, this new photo-Fenton catalyst has great potential for the photocatalytic degradation of dye contaminants in water.

The role of La3+ substitution in modification of the magnetic and dielectric properties of the nanocrystalline Co-Zn ferrites

Co-Zn spinel ferrites with lanthanum (La3+) ion substitutions having formula Co0.7Zn0.3LaxFe2-xO4 (x = 0.0, 0.025, 0.05, 0.075, 0.1) were prepared using sol gel auto ignition route. The structural characterization of the ferrites was performed by the x-ray diffraction (XRD) method. The parameters calculated from the XRD analysis include lattice parameter, density, porosity, crystal size and lattice strain. The nanocrystallinity of the ferrite samples was observed with the crystallites of 20–30 nm size. The scanning electron microscopy (SEM) was employed to analyse the morphology of the ferrite crystals. The size and shape of the ferrite nanocrystals were confirmed from transmission electron microscopy (TEM) images. The crystal planes revealed from XRD calculations were confirmed by the selected area electron diffraction (SAED) analysis of the ferrites. Vibrating sample magnetometer (VSM) measurements of the ferrite samples were performed to study the magnetic properties of the ferrites. The effects of the La3+ substitution were observed on the coercivity and saturation magnetization of the ferrites. The variation of dielectric properties of the ferrites within 50 Hz to 5 MHz frequency band were studied at room temperature. The dielectric relaxation in the ferrites was governed by the electron hopping between divalent (Fe2+ and Co2+) and trivalent (Fe3+ and Co3+) cations. Remarkable impact of La3+ composition and the crystal size was observed on dielectric constant as well as loss tangent.

Non-hydrolytic synthesis of caprylate capped cobalt ferrite nanoparticles and their application against Erwinia carotovora and Stenotrophomonas maltophilia.

Magnetic cobalt Ferrite nanoparticles capped with caprylate groups, CH3(CH2)6CO2-, have been synthesized using a novel non-hydrolytic coprecipitation method under inert conditions. Particle diameter was characterized using dynamic light scattering (DLS) and transmission electron microscopy (TEM). The spinel ferrite crystal phase was verified using X-ray diffraction (XRD), and the presence of the capping agent was confirmed using Fourier Transform Infrared spectroscopy (FTIR). Bactericidal effects of the particles were tested against broth cultures of Erwinia carotovora and Stenotrophomonas maltophilia. The final particles had an average diameter of 3.81 nm and readily responded to a neodymium magnet. The particles did have a significant effect on the OD600 of both broth cultures.

The Experiments Detecting of Real Magnetic Charges in Structures of Atoms and Substance

Magnetic neutron scattering in Y-type hexagonal ferrite crystals, studied by the author in 1968-1971 and presented in the article showed that the entire density of the so-called magnetic moments of Fe3+ ions can significantly shift from the position of their nuclei. As result of these shift the structure in form of the chain magnetic spiral is realized in ferrite lattice. The noted shifts of the “magnetic moments” served as the basis for the author’s assumption that these “moments” are “fig sheets” behind which the magnetic poles (magnetic charges) real existing in the shells of atoms are hidden. In this case, the scattering of neutrons is carried out by magnetic charges, and not theoretical surrogates in the form of magnetic moments. In addition to participating in atomic structures, magnetic charges populate potential conduction zones in conductors, where they are exist in compositions of magnetic dipoles. Under the influence of an external magnetic field, a polarization of magnetic dipoles is realized in the conductor, the field strengths of which are directed against the external magnetic field. It is these dipole magnetic fields that are responsible for such a well-known physical phenomenon as diamagnetism. Under the conditions of noted polarization of magnetic dipoles the author managed to perform mechanical separation of magnetic charges in pairs ±g and to charge experienced bodies (metal plates) by the magnetic charges of one sign. The fact of such a charging was detected through magnetostatic interaction between magnetic charges on the plates using highly sensitive torsion balances. This experiment is presented in detail in this article. The results of these experiments, as well as subsequent experimental and theoretical studies of the author, which, in general composition, were carried out from 1968 to the present, showed that magnetic charges are real structural components of the atoms and substance. So, for example, the atomic shells are not electronic but electromagnetic. The main reason that real magnetic charges were “buried alive” in the existing physical theories is the physics of their confinement in substance forces of which, in its rigidity, is many times greater than the electron confinement forces.

Elastic Properties of Cr-doped Mn Ferrite

BackgroundThe mechanical properties of Mn-Cr ferrite of different compositions are important for industrial applications in everyday life. Ferrites are used in electric choke coils, electric transformers, and many other electronic and optical devices. The elastic properties can be understood by studying the longitudinal sound velocity (Vl) and shear velocity (Vs).ResultsThe longitudinal sound velocity (Vl) and shear velocity (Vs) are measured at room temperature by pulse transmission technique at the frequency of 1659 Hz, which is ideally representing the mechanical properties of the ferrite crystal. The shear sound velocity was found to be around 4 × 103 m∕s while the longitudinal sound velocity was ranging according to the doping concentration from 6 × 103 to 1 × 104 m∕s. The behavior of Young’s modulus (E), rigidity modulus (n), mean sound velocity (Vm), and Debye temperature (θD) is quite similar, where a change in the slope was noticed at Cr concentration higher than 0.7 in the spinel lattice.ConclusionWe have characterized the elastic properties of the spinel structure Mn-Cr ferrite with different Cr ion concentration at a fixed sound frequency using the pulse transmission technique. The longitudinal sound velocity showed an increase with increasing Cr ion concentration, the rigidity constant as well as Debye temperature, Isotropic compressibility, and the acoustic impedance showed behavioral change at Cr ion concentration x = 0.7 which is correlated to the intra-ionic distances change due to the replacement of Fe ions with smaller size Cr ions.

Crystallization, non-isothermal kinetics and structural analysis of nanocrystalline multiferroic bismuth ferrite (BiFeO3) synthesized by combustion method

The synthesis of bismuth ferrite (BiFeO3) in the nanocrystalline form is described in the present work with the help of self-combustion technique with DL-malic acid as fuel to obtain single-phase BiFeO3 nanopowders. The crystallization behavior for the formation of BiFeO3 was confirmed from the obtained powder diffraction pattern (p-XRD) and thermogravimetric analysis with simultaneous differential thermal analysis. Thermal measurements were carried out in the nitrogen atmosphere to determine the crystallization kinetics through various heating rates from simultaneous thermogravimetric–differential thermal (TG–DTA) analysis curve. The activation energies for the formation of BiFeO3 metal oxides formation were found to be around 124 kJ mol−1 and 113 kJ mol−1 from the phenomenological Johnson–Mehl–Avrami equation or in short JMA. The growth mechanism along three dimensions was observed for all heating rates. The formation of single-phase BFO in nanocrystalline nature was confirmed through microstructural investigations by the use of transmission electron microscopic analysis. The selected area electron diffraction pattern of nanostructure bismuth ferrite for the sample calcinated at 800 °C reveals the diffraction miller indices planes {104} and doublet peaks of {110}, {202} which is in good agreement with that of the present powder XRD pattern. The magnetization for the synthesized samples calcinated indicates that there exists the magnetic order and existence of room-temperature magnetic saturation for the multiferroic BiFeO3.

Compact four-port circulator based on 2D photonic crystals with a 90° rotation of the light wave for photonic integrated circuits applications

A four-port optical circulator based on two-dimensional square lattice photonic crystals is reported. It is simple besides the brief framework. The crystalline geometrical structure of the circulator makes 90° non-reciprocal transmissions of electromagnetic waves with low insertion loss and high levels of isolation by the diligence of magneto-optic crystals. The structure is novel because it uses a resonant cavity with a simple design. Also, in comparison to prior models, the proposed four-port circulator utilizes a two-dimensional square lattice crystal structure with a cylindrical ferrite section of the π/4 Faraday angle. The finite element method is used for this anisotropic medium to get the tensor elements in this simulation. The importance of the gyromagnetic properties of ferrite crystals for the non-reciprocal transmission is investigated. Furthermore, the corresponding S-parameters for this circulator are analyzed and reported. Due to the compact size and ease of fabrication, this device can be realized for applications such as splitting and isolation in photonic integrated circuits.