Isothermal investigation of decomposition of FeSO4·H2O-BaO2 mixtures

Isothermal studies were conducted on mixtures of Fe₂SO₄·H₂O in BaO₂ in molar ratios ofn=4, 2 and 1 at temperatures of 573 and 1073 K, in a closed crucible, in air as gas medium. The solid products of decomposition were investigated by means of X-ray analysis, Mössbauer spectroscopy and electron spectroscopy.The experiments revealed that the mechanism of the process is connected with the formation of different quantities of barium ferrites (BaFeO₃, BaFe₂O₄ and BaFe₁₂O₁₉), as well as BaSO₄ and Fe₂O₃, depending on the quantity of BaO₂ in the initial mixture, the partial pressure of the gas components and temperature. Differences were found in the mechanism of the process for the same mixtures under dynamic temperature conditions.     

The impact of highly paramagnetic Gd3+ cations on structural,spectral, magnetic and dielectric properties of spinel nickel ferrite nanoparticles

In this work, fabrication of Gd³⁺ substituted nickel spinel ferrite (NiGd_xFe_2-xO₄) nanoparticles was carried out via co-precipitation route. X-ray powder diffraction (XRD) confirmed the spinel cubic structure of NiGd_xFe_2-xO₄ nanoparticles. XRD data also facilitated to determine the divalent and trivalent metal cations distribution at both A and B sites of the ferrite lattice. Site radii, hopping and bond lengths were also calculated from XRD data. The spectral studies elucidated the formation of cubic spinel ferrite structure as well as stretching vibrations of M–O (metal–oxygen) bond at A and B sites of ferrites, represented by two major bands υ₁ and υ₂ respectively. FESEM analysis confirmed the irregular morphology of NiGd_xFe_2-xO₄ nanoparticles. EDX spectrographs estimated the elemental compositions. The dielectric attributes were explained on the basis of the Debye-relaxation theory and Koop’s phenomenological model. At higher applied frequencies (AC) no prominent dielectric loss was observed. Magnetic parameter variations can be attributed to the substitution of the rare earth cations having larger ionic radii as compared to the radii of Fe³⁺ ions. Moreover, spin canting, magneto-crystalline anisotropy and exchange energy of electrons also helped in magnetic evaluation. Due to small coercivity values NiGd_xFe_2-xO₄ nanoparticles can be employed significantly in high-frequency data storage devices.     

Study of DC conductivity and relative magnetic permeability of nanoparticle NiZnFe2O4/PPy composites

The DC conductivity and the relative magnetic permeability have been measured as functions of temperature for five powder samples of nanoparticle ferrites (Ni_xZn_1−xFe₂O₄; x=0, 0.25, 0.5, 0.75 and 1), a pure polypyrrole (PPy) powder sample and many composite samples prepared by mixing different ratios of the ferrites to PPy. By comparing the results it is found that there is an obvious increase in DC conductivity of the ferrite/PPy composite samples compared to the corresponding pure ferrite samples, whereas compared to the pure PPy sample there is a decrease in DC conductivity. On the contrary, the magnetic permeability of the composites is higher than that of the pure PPy sample and lower than that of the pure ferrite samples as was expected.     

MFM studies of magnetic domain patterns in bulk barium ferrite (BaFe12O19) single crystals

Magnetic domain patterns in bulk barium ferrite (BaFe₁₂O₁₉; BaM) single crystals on the basal plane and the prism plane were measured and studied by magnetic force microscopy (MFM). The surface domain pattern is in the form of flowers or star on the basal plane and long elongated spikes or stripe domains on the prism plane. The change in domain structure with applied field (H_app) and the thickness (T) dependence on domain width (δ) was observed. The domain width decreased from 32 to 9 μm for the crystals of 800-100 μm thicknesses, respectively.     

Glass additive influence on the sintering behavior, microstructure and microwave magnetic properties of Cu-Bi-Zn co-doped Co2Z ferrites

The Bi₂O₃-B₂O₃-ZnO-SiO₂ (BB35SZ) glass effects on the sintering behavior and microwave magnetic properties of Cu-Bi-Zn co-doped Co₂Z ferrites were investigated to develop low-temperature-fired ferrites. The glass wetting characteristics on the Co₂Z ferrite surface, X-ray diffractometer, scanning electron microscopy and a dilatometer were used to examine the BB35SZ glass effect on Co₂Z ferrite densification and the chemical reaction between the glass and Co₂Z ferrites. The results indicate that BB35SZ glass can be used as a sintering aid to reduce the densification temperature of Co₂Z ferrites from 1300 to 900 °C. 3(Ba_0.9Bi_0.1O)·2(Co_0.8Cu_0.2O)·12(Fe_1.975Zn_0.025O₃) ferrite with 2 wt% BB35SZ glass can be densified below 900 °C, exhibiting an initial permeability of 3.4. This process provides a promising candidate for multilayer chip magnetic devices for microwave applications.     

钴铁氧体/膨胀石墨及其聚吡咯复合物的制备和油水分离性能

用化学共沉淀法和原位乳液聚合法分别制备了钴铁氧体/膨胀石墨复合微粒(CF/EG)和钴铁氧体/膨胀石墨/聚吡咯复合物(CF/EG/PPy)。用现代分析技术表征了样品的组成、结构、形貌、电-磁性能和油水分离性能。结果表明,CF粒子已填嵌入到膨胀石墨的层间,CF/EG/PPy复合物的核(CF/EG)和壳(PPy)之间存在着一定的相互作用,样品的油水分离效果与膨胀石墨的层间空隙成正比,其次序为:EG>CF/EG>CF/EG/PPy。磁性的CF/EG微粒回收容易,重复使用性能优良,循环5次的效率不低于90%。     

Microstructural,magnetic and dielectric performance of rare earth ion (Sm3+)-doped MgCd ferrites

The combined effects of Sm$^{3+}$ substitution together with the addition of 3 wt% Bi$_{2}$O$_{3}$ endow MgCd ferrites with excellent magnetic permeability and dielectric permittivity. Various concentrations of Sm$^{3+}$ ($x = 0$, 0.03, 0.06, 0.09, 0.12 and 0.15) were employed to modify the permeability ($\mu'$) and permittivity ($\varepsilon'$) of the MgCd ferrites. X-ray diffraction, scanning electron microscopy (SEM), vibrating sample magnetometry and vector network analysis techniques were used to characterize the samples. The measurement results reveal that the ferrites processed a saturation magnetization of up to 36.8 emu/g and coercivity of up to 29.2 Oe via the conventional solid-state reaction method. The surface morphology SEM confirms that with increasing Sm$^{3+}$ concentration, the grain shape changes from a polygon to a circle. Moreover, the dielectric permittivity can reach a value of 23. The excellent properties obtained in Sm$^{3+}$-substituted Mg ferrites suggest that they could be promising candidates for modern high-frequency antenna substrates or multilayer devices.     

Long-range ordering in the Bi1−xAexFeO3−x/2 perovskites: Bi1/3Sr2/3FeO2.67 and Bi1/2Ca1/2FeO2.75

Two-ordered perovskites, Bi_1/3Sr_2/3FeO_2.67 and Bi_1/2Ca_1/2FeO_2.75, have been stabilized and characterized by transmission electron microscopy, Mössbauer spectroscopy and X-ray powder diffraction techniques. They both exhibit orthorhombic superstructures, one with a≈b≈2a_p and c≈3a_p (S.G.: Pb2n or Pbmn) for the Sr-based compound and one with a≈b≈2a_p and c≈8a_p (S.G.: B222, Bmm2, B2mm or Bmmm) for the Ca-based one. The high-resolution transmission electron microscopy (HRTEM) images evidence the existence of one deficient [FeO_x]_∞ layer, suggesting that Bi_1/3Sr_2/3FeO_2.67 and Bi_1/2Ca_1/2FeO_2.75 behave differently compared to their Ln-based homolog. The HAADF-STEM images allow to propose a model of cation ordering on the A sites of the perovskite. The Mössbauer analyses confirm the trivalent state of iron and its complex environment with three types of coordination. Both compounds exhibit a high value of resistivity and the inverse molar susceptibility versus temperature curves evidence a magnetic transition at about 730 K for the Bi_1/3Sr_2/3FeO_2.67 and a smooth reversible transition between 590 and 650 K for Bi_1/2Ca_1/2FeO_2.75.     

The magnetocaloric effect of superfine magnets

The magnetocaloric effect (MCE) of aqua suspensions based on superfine magnetite (Fe₃O₄), hematite (α-Fe₂O₃), maghemite (γ-Fe₂O₃), samarium ferrite (SmFe₂O₄) and gadolinium ferrite (GdFe₂O₄) as well as of magnetite-based ferrofluids was calorimetrically determined in the range of the temperatures from 283 to 253 K. MCE has a positive magnitude for all investigated systems except a hematite-based system. For the suspensions on the basis of MCE temperature dependence it was determined that superfine magnetite transformed into α-Fe₂O₃ at the temperature above 328 K in contrast to monocrystal magnetite. For aqua suspensions of samarium ferrite and gadolinium ferrite and magnetite-based ferrofluids MCE temperature dependence has an extreme behavior which is connected with a second-order phase transition. For the first time it is established that the magnetocaloric effect (MCE) is greatly increased when the magnet is a nanosized material.     

Cu–Ce substituted cobalt nano ferrite - Structural,morphological, and magnetic behavior prepared by sol-gel auto-combustion

Sol-gel auto-combustion synthesized Co_1-xCu_xFe_2-yCe_yO₄ (x = 0.0, 0.25, 0.5 and 0.75; y = 0.0, 0.03, 0.06, and 0.09), Cu–Ce substituted Co ferrite nanopowders. Investigations have been done on how Cu–Ce substitution affects the structural and magnetic characteristics. The Cu–Ce substitution variation effect on structural and magnetic properties is studied with X-ray diffraction (XRD), Field effect scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy (FTIR), and Vibrating sample magnetometer (VSM). The XRD was used to identify the crystal phase, and the role of Cu–Ce substituted for Co indicates how it formed. There is no change in the crystal structure, and no additional characteristic peak linked to Cu²⁺ and Ce³⁺ ions substitution was found in the XRD. The powder was sintered at 1100 °C. The crystallite sizes were found in between 33 and 62 nm. Increasing the Cu–Ce content decreases the lattice constant and is found between 8.4044 and 8.3309 Å. The FESEM images were used to analyze the nanostructural properties. The range of 110–128 nm is the value of average grain size. Two vibrational bands can be seen in FTIR spectra at about 600 cm⁻¹ (v₁) and 400 cm⁻¹ (v₂). They are attributed to the spinel lattices A and B sites, respectively. The tetrahedral site has a greater vibrational frequency of 566.09 cm^−1, while the octahedral site has a lower vibrational frequency of 420.09 cm⁻¹. FTIR spectra show the tetrahedral stretching peaks shifting towards lower frequencies with increasing Cu²⁺ and Ce³⁺ ions content. At ambient temperature, the magnetic properties of Cu–Ce substituted cobalt ferrites revealed a strong hysteresis loop. There was a decrease in magnetic saturation and an increase in coercivity.