Narrow Results

An analysis to the characteristics of Co, Mg and Cu ferrites that were prepared using sol–gel method and annealed at $800^{\circ }$C for 1 hour, performed using X-ray diffraction and Raman spectroscopy for structural characteristics, while the Vibrating Sample Magnetometer (VSM), was used for the magnetic characteristics. The X-ray analysis of both cobalt and magnesium ferrites shows a reverse crystal structure of a cubic spinel, while copper ferrite shows a tetragonal crystal structure characteristic at this annealing temperature. The lattice constant (a) was found to be $a=8.186$ for CoFe₂O₄, $a=8.199$ for MgFe₂O₄ and $a=5.969$ for CuFe₂O₄. The Raman spectrum confirms a spinel crystalline form of the prepared ferrites where a likely distribution of cation is indicated at the tetrahedral and octahedral sites. The peaks of the Raman shift appear between 200–800cm${}^{-1}$. These peaks indicate the formation of ferrites. The hysteresis loop of CoFe₂O₄ indicates a hard magnet material. Cu ferrites have relatively lower remnants and magnetocrystalline anisotropy, which indicates soft magnetic characteristics even though it showed higher coercivity. The squareness ratio (Mr/Ms) values varied between 0.52, 0.13 and 0.57 for CoFe₂O₄, MgFe₂O₄ and CuFe₂O₄, respectively. These insights highlight the possibility of tuning the properties of ferrites using a cost-effective sol–gel method.

This study investigates Beam Line Absorbers (BLAs) for the Hefei Advanced Light Facility (HALF). A ferrite-based BLA prototype was developed, demonstrating high-power handling capacity up to 10kW, ultra-high vacuum performance better than $6.5\times 10^{-10}$ mbar, and high absorption efficiency in critical frequency ranges. Subsequently, more compact designs with reduced longitudinal length were explored, investigating ferrite-only, silicon carbide (SiC)-only, and hybrid configurations through RF simulations. Based on preferred absorption efficiency, ferrite-only and hybrid BLA structures were further analyzed under high-power conditions. Referencing test results, multiphysics simulations were conducted under 3kW absorbed power. The hybrid design, comprising two rings of ferrite tiles and one ring of SiC tiles, improved the temperature distribution of the absorbing materials. Extrapolating to 11kW absorbed power, this design reduced the maximum temperatures on absorbing tiles by up to 40$°$C compared to the ferrite-only design. The hybrid design offers a balanced solution that combines effective HOM damping with enhanced thermal performance, improving the long-term operational stability of BLAs.

In this paper, dielectric properties of Ni_xMn_0.4-xZn_0.6Fe₂O₄ ferrites with x varying from 0.05 to 0.35 prepared by the citrate precursor method have been investigated as a function of frequency, temperature, composition, and sintering temperature. A decrease in the dielectric constant is observed with the increase in Ni concentration except for x = 0.3. This decrease in dielectric constant with the increase in Ni concentration is justified by inverse proportionality between resistivity and dielectric constant. Dispersion in the dielectric constant with frequency in the range of 75 Hz to 30 MHz is observed. Resonance peaks were observed in tan δ_ε versus frequency curve for all the samples. A shift in the resonance frequency toward higher frequency is observed with the increase in temperature. The peak height also increases with an increase in temperature. Phase change is confirmed by differential scanning calorimetry. Structural studies have been done by X-ray diffraction technique and scanning electron microscopy. Possible theories, models, and mechanisms contributing to these processes have been discussed.

Nanocrystalline spinel Zn–Cu–Cr ferrites with Gd substitution were prepared by a rheological phase reaction method. By means of the Fourier transform infrared (FTIR) spectra, Raman spectra, and X-ray diffraction (XRD), the cubic spinel structure of samples had been confirmed. The magnetic parameters such as saturation magnetization, remanent magnetization and coercivity can be tailored by controlling the content of substituting Gd ions.

The zinc and aluminum co-substituted cobalt ferrite of the series Co_1-xZn_xFe_2-xAl_xO₄ were prepared by wet chemical co-precipitation method. The variation of lattice constant and jump length of electron of wet and annealed samples was studied. The variation of lattice constant and jump length of electron of wet and annealed wet samples shows that it increases up to x=0.2 thereafter x>0.2 it decreases in both the cases. In the present work the values of tetrahedral and octahedral bond length (d_Ax) and (d_Bx), shared tetrahedral and octahedral edge was also studied. The cationic distribution is calculated on the basis X-ray diffraction method. The cation distribution estimated from X-ray intensity ratio calculations suggest that, Zn²⁺ ions occupies only tetrahedral (A) site whereas Al³⁺ ions occupies both tetrahedral (A) and octahedral [B] sites.

The systems MgCuZnFe₂O₄ doped (0–0.6 wt% Ta) are prepared by the general ceramic method using the sintering temperature at 1200°C. The variations of the sintered density, lattice parameter, jump length of electrons, and initial permeability were studied. A maximum density was obtained at 1200°C during the preparation process. The electrical resistivity decreases with increasing tantalum (Ta) content upto 0.1 wt% and then increases for higher concentrations. The initial permeability and the change carries mobility increase upto 0.1 Ta and then decreases. The jump length decreases with enhancing Ta ions because the substitution of Ta ion with small size instead of Fe³⁺ at the A sites increase the concentration of iron ions at the B sites. The increase of the iron content causes the decrease of the jump length of electrons between Fe³⁺ and Fe²⁺. These improvements of the magnetic properties give some light about the importance of these compositions to be used in technology.

Fe–6.5 wt.% Si powder coated with 10 wt.% MnZn(Fe₂O₄)₂ (MnZn ferrite) was successfully prepared by using dry-type stirring ball milling. The Fe–6.5 wt.% Si/MnZn(Fe₂O₄)₂ soft magnetic composites were prepared by subsequent spark plasma sintering. This paper aims at analyzing the microstructure and magnetic properties of Fe–6.5 wt.% Si/MnZn(Fe₂O₄)₂ soft magnetic composites (sintering temperature: 750${}^{\circ }$C, sintering pressure: 50 MPa, holding time: 8 min, heating rate: 60 K/min). Based on X-ray diffraction and scanning electron microscopy, microstructure and powder morphology were examined and magnetic measurements on bulk samples were conducted by vibrating sample magnetometer and impedance analyzer. According to the experiments results, Fe–6.5 wt.% Si/MnZn(Fe₂O₄)₂ composites displayed a core-shell structure, and ceramic phase was observed after sintering. The Fe–6.5 wt.% Si/MnZn(Fe₂O₄)₂ composites achieved high resistivity ($\rho :2.9$ m$\mathrm{\Omega }$/cm) while maintaining excellent magnetic properties ($M_s:174.00$ emu/g). Core losses especially at medium and high frequencies were significantly reduced.

The effect of Cr³⁺ concentration on the various hyperfine interactions for the ferrite system Li_0.5+tCr_xSb_tFe_2.5-2t-xO₄, 0.0 ≤ x ≤ 1.0, x in steps of 0.2 and t = 0.1, have been studied at room temperature using Mössbauer spectroscopy. The isomershift and the quadrupole splitting are almost negligibly influenced by the change in chromium level. The internal nuclear magnetic field, as determined from the Mössbauer spectra and the linewidth are also studied with the variation of composition. The results have been explained on the basis of various models and a cation distribution has been worked out.

Dielectric properties such as dielectric constant (ε′) and dielectric loss tangent (tan δ) of Li_0.5+xFe_2.5-2xSb_xO₄ ferrites, 0.10≤ x ≤0.30 in steps of 0.05 have been investigated as a function of composition, frequency and temperature. The dielectric constant showed dispersion with frequency in the range of 100 Hz–1 MHz. Peaks were observed in the tan δ versus frequency curves for almost all the samples. The temperature variation of dielectric constant for the different samples was studied at 10 kHz in the temperature range from room temperature to 433 K. Peaks were observed for some of the samples. The peaks were seen to shift towards higher temperature region as the substitution level increases. The mechanisms involved in the processes are discussed in this paper.

Processing of ferrites has gained tremendous importance in recent times in order to meet high performance demands on ferrites in keeping with the fast emerging technologies. The main focus of research in the 21st century is towards the formation of smaller magnetic particles. In normal ceramic methods we cannot control particle size and porosity, whereas in precursor methods we can control both. In the present study we have synthesized Mg_0.9Mn_0.1Fe₂O₄ ferrites by the normal ceramic method and the citrate precursor method. By the citrate method we have simultaneously reduced the particle size and sintering temperature as compared to the normal ceramic method. By the citrate method, direct current (DC) resistivity is increased by two orders of magnitude, and electrical as well as magnetic losses are reduced as compared to the normal ceramic method. The initial permeability is reduced in both citrate method as compared to the normal ceramic methods. However, with sintering temperature the initial permeability increases. The dielectric constant is reduced by the citrate method as compared to normal ceramic methods. These observations are explained on the basis of various mechanisms and models.

CoLa_xFe_2-xO₄ (x = 0.00, 0.05 and 0.1) nanoparticles were prepared simply by a modified citrate precursor route. Effects of La-substituting level on the their magnetic properties were investigated on the basis of the structural analysis. The thermal evolution of the precursor, as well as the microstructure of as-prepared products were studied by means of a thermogravimetric analyzer (TGA), X-ray diffractometer (XRD) and Fourier transform infrared (FTIR) spectrometer. The magnetic properties of the as-prepared samples were measured using a vibrating sample magnetometer (VSM). It was found that the magnetic properties were dependent on many factors such as La-substituting level, particle size and microstructure. The observed saturation magnetization decreased with increasing La content, whereas coercivity exhibited reverse behavior.

Expressions for the effective permeability tensor of two-component partially magnetized ferrite-like metamaterials are obtained in the microwave frequency range. The formulas are based on the theory of partially saturated conventional ferrites and the effective medium theory (EMT) of metamaterials presented in a form of an infinite host dielectric medium with periodically embedded ferric cylindrical and spherical inclusions partially magnetized with an external bias DC magnetic field. The low-field losses absence conditions are obtained for the metamaterials under the assumption of a low phenomenological loss term and losses are estimated.

The objective of mechanical stress sensor is to measure the applied pressure or provide control standard to the process. In order to accomplish this, most of the stress sensors convert mechanical stress into electronic signal. Ferrites are the best known magnetic semiconductors. This paper brings out the variation in inductance of the micro-inductor made from ${\mathrm{\text{Ni}}}_{0.42}{\mathrm{\text{Cu}}}_{0.10}{\mathrm{\text{Zn}}}_{0.6}{\mathrm{\text{Fe}}}_{1.76}{\mathrm{\text{O}}}_{3.76}$ on application of mechanical stress. ${\mathrm{\text{Ni}}}_{0.42}{\mathrm{\text{Cu}}}_{0.10}{\mathrm{\text{Zn}}}_{0.6}{\mathrm{\text{Fe}}}_{1.76}{\mathrm{\text{O}}}_{3.76}$ ferrite nanoparticles are synthesized by sol–gel autocombustion technique. The ferrite powder thus obtained is double sintered at 450${}^{\circ }$C and 870${}^{\circ }$C in a microwave furnace. The X-ray diffraction pattern of the ferrite confirms spinal structure. The frequency spectrum of dielectric constant is done in the range of 100 to 5 MHz frequency. The variation of inductance $(\Delta L/L)$% with applied compressive stress on the micro-inductor made from the ferrite is measured in the range of 0–8 MPa.

We theoretically propose a system capable of wavelength-tunable sub-diffraction-limited imaging by a single planar magnetic superlens, which is made of $\mu$-negative ferrite material (MNM) slab. Our theoretical and numerical simulation results demonstrate that the working wavelength of this planar superlens can be well tuned with the external magnetic field since the permeability of ferrite material LuBiIG is adjusted by the applied magnetic field. The resolution of the magnetic superlens with 300 $\mu$m thickness LuBiIG film is smaller than $\lambda$/20, and the resolution is higher with thinner film. It may provide a potential way to design a wavelength-tunable magnetic superlens with the single layer of ferrite thin film material.

Chromium-doped manganese–zinc ferrite samples were prepared by solid-state reaction route to probe the effect of chromium ion on the crystal and lattice structure of mixed manganese–zinc ferrite. X-ray diffraction patterns reveal that Mn${}_{0.5}$Zn${}_{0.5-x}$Cr${}_x$Fe${}_2$O${}_4$ ($x$ = 0.0, 0.1, 0.2, 0.3, 0.4 and 0.5) ferrite has polycrystalline cubic spinel structure with some secondary phase of $\alpha$–Fe${}_2$O${}_3$. The Raman spectra reveal four Raman active phonon modes in the measurement range of 200–750 cm${}^{-1}$ with small shift in Raman modes towards higher wave number. The average particle size for Mn${}_{0.5}$Zn${}_{0.5}$Fe${}_2$O${}_4$ is found to be 37.28 nm which reduces to 33.64 nm for Mn${}_{0.5}$Cr${}_{0.5}$Fe${}_2$O${}_4$. As the ion doping of chromium increases, the modes of vibration are found to shift towards higher wavelength and blueshift is attributed to the higher ionic radii of Cr${}^{2+}$ as compared to Zn${}^{2+}$.

Molecular dynamics simulation was adopted to investigate the nanoscale titanium nitride formation at the early formation stage in high-strength low-alloy steel. During the cluster formation process, the nitride clusters were formed through the atom aggregation. The atomic interactions of titanium and nitride atoms were revealed and the cluster property was discussed. The nanoscale titanium nitride clusters own a wide composition, and the cluster formation mechanism was concluded.

Cobalt substituted nickel zinc ferrite nanoparticles (Ni_0.65–xCo_xZn_0.35Fe_2.0O₄) X varying from 0.0 to 0.65 in steps of 0.15 have been produced using sol–gel method, with PVA as chelating agent. The phase formation of the sintered ferrite was confirmed by X-ray diffraction studies. The lattice parameter a(A°) has been calculated using Nelson–Riley method. The crystallite size has been estimated by the Williamson–Hall method using the full width at half-maximum (FWHM) of the line broadening of all the peaks. Mössbauer spectroscopy (MS) of the samples showed the clear presence of two sextets and distribution of iron over the two sites has been given. Increase in saturation magnetization with cobalt concentration with a slight decrease for x = 0.15 has been observed with the vibrating sample magnetometry study. The observed value of magnetization for Ni_0.65Zn_0.35Fe₂O₄ with a particle size of 43.5 nm has been 71 emu/gm at room temperature, which is higher than that reported for samples prepared using chemical methods of the same composition. The results have been explained on the basis of the particle size and cation distribution among various sites.

Ni_0.65Zn_0.35Fe₂O₄ nanoparticles synthesized by sol–gel process have been subjected to various annealing temperatures with a view of obtaining size dependent properties and critical length. X-ray diffraction, transmission electron microscopy, VSM and ESR experiments were carried out as a function of crystallite size. From the ESR spectra it has been observed that the sample annealed at 1025°C has least magnetic anisotropy. The observed variations in saturation magnetization and coercive field have been explained in terms of magnetic anisotropy.

Properties of nanoscale materials are very interesting and these are either comparable to or superior to those of bulk. These materials are interesting due to their exciting size dependent optical, electronic, magnetic, thermal, mechanical and chemical properties. Different mole ratios of nanostructured mixed metal oxides of LaCo_xFe_1-xO_3-δ (x = 0 to 1) were prepared by the sol–gel method by varying the mole ratios of iron and cobalt substrates. The compounds were sintered for 700°C in the tubular furnace for 8 h. The purity of the compounds was analyzed by TG-DTA. The compounds were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) and scanning electron microscopy (SEM) studies were employed to study the structural phases, vibrational frequencies, surface morphology of the highest humidity sensing compounds.

A series of polycrystalline bulk samples of Mn_1+xFe_2-2xTi_xO₄ (0 ≤ x ≤ 0.5) have been prepared by using a conventional solid-state reaction method. The effect of Ti⁴⁺ ions substitution on magnetic and electronic structure of MnFe₂O₄ has been studied using isothermal d.c. magnetization and near edge X-ray absorption fine structure spectroscopy (NEXAFS) measurements. The magnetization studies infer that all samples have ferrimagnetic ordering at room temperature. The magneton number (n_B) calculated using the magnetic hysteresis loop has been found to decrease linearly with the Ti substitution, which indicates that the system follows the Neel's two sub-lattice model. The decrease in the value of n_B may be due to the dilution of the sub-lattice by Ti ions. The NEXAFS measurements performed at Fe/Ti L_{3, 2} edges indicate that Fe ions are in mixed valence state whereas Ti ions remain unchanged at 4⁺ state.