Influence of Sm-substitution on structure and electromagnetic properties of Ba3−xSmxCo2Fe24O41 powders

Sm-substituted barium hexaferrites, Ba_3−xSm_xCo₂Fe₂₄O₄₁ (x=0-0.25), were prepared by a conventional ceramic sintering method. The microstructure, complex permittivity, complex permeability and static magnetic properties of the samples were studied using powder X-ray diffraction, field emission scanning electron microscopy, vector network analyzer and vibrating sample magnetometry. The results reveal that by introducing a relatively small amount of Sm³⁺ instead of Ba²⁺ an important modification of both structure and high-frequency electromagnetic properties can be obtained. Doping of Sm³⁺ suppressed the grain growth and gave rise to a decrease of the grain size. As the Sm content increases, the static magnetic properties continuously increase. The real part and imaginary part of complex permittivity initially increase with Sm content, and then decreases when x>0.10. The imaginary part of complex permeability decreases after Sm³⁺ is doped. There is no obvious change in the real part of the complex permeability for different Sm contents. The reasons are discussed using electromagnetic theory.     

Synthesis and characterization of poly(3-thiophenyl acetic acid) (P3TAA)-BaFe12O19 nanocomposite

We have presented a method for the fabrication of poly(3-thiophenyl acetic acid) (P3TAA)-BaFe₁₂O₁₉ nanocomposites by the in situ polymerization of P3TAA in the presence of synthesized BaFe₁₂O₁₉ nanoparticles. The nanoparticles and the nanocomposite were analyzed by XRD, FTIR, TGA, TEM, VSM and conductivity techniques for structural and physicochemical characteristics. Crystallographic analysis revealed the phase as hexaferrite and X-ray line profile fitting yielded a crystallite size of 32 nm. The particles, observed by TEM, exhibit irregular shapes and sizes between 100 and 500 nm, revealing polycrystalline character when compared with the crystallite size from XRD. FTIR and TGA analysis results show that P3TAA is conjugated to the particle surface via a carboxylate group and that the composite has a polymer content of ∼10%. Magnetic hysteresis curves do not saturate at high fields, which is a characteristic feature of fine particle systems with grain sizes smaller than 1 μm. Conductivity measurements showed a semiconductor character of the nanocomposite.     

Magnetic and electromagnetic properties of RuZn and RuCo substituted BaFe12O19

Polycrystalline samples of M-type hexaferrites BaFe_12−2xRu_xZn_xO₁₉ and BaFe_12−2xRu_xCo_xO₁₉ with 0x0.45 have been prepared by a classical sintering method. The evolutions with x of the cell parameters, the saturation magnetization and the magnetic transition temperature have been measured; in this range of small doping ratios, saturation magnetization and Curie temperature of substituted hexaferrites remain close to those of the undoped BaFe₁₂O₁₉. X-ray diffraction measurements on oriented powders show that a change of magnetocrystalline anisotropy from axial to planar occurs in both cases for a small substituting ratio x_c=0.375. Microwave electromagnetic characteristics have been studied on the ceramic samples from 0.1 to 10 GHz. The behaviour of the magnetic losses (μ″) corroborates the anisotropy change when doping; a convolution of the dissipation mechanisms (domain wall motions and gyromagnetism) is obtained for x_c. The level of the magnetic losses is discussed in relation with others substituted Ba-hexaferrites.     

Application of FORC distributions to the study of magnetic interactions in ferrites of composition

Magnetic interactions in hexaferrite samples of Ba_1-xLa_x+δFe_12-xCo_xO₁₉ composition were studied. The precursor powders—barium carbonate (BaCO₃), lanthanum oxide (La₂O₃), hematite (Fe₂O₃) and cobalt acetate—were milled for 100 h in air atmosphere and heat-treated for 1 h at . The structural characterization was performed by X-ray diffraction. The FORC distributions show a single peak at high switching fields, indicating that the substituted systems are formed by weakly interacting particles. La excess induces the decoupling of the particles.     

Magnetic and structural properties of M-type barium hexaferrites films with transition metal substitutions

We have investigated the correlation between structural and magnetic properties of M-type BaFe₁₂O₁₉ thin films (～1.4 $\mu m$) with Co-Ti (magnetic/non-magnetic) and Co-Ni(magnetic/magnetic) substitution, as BaFe_12-2xCo_xTi_xO₁₉ and BaFe_12-2xCo_xNi_xO₁₉ (0?≤?x?≤?1). With structural properties sensitively related to the magnetic properties, where ferro-ferri phase transition is involved, it has been found that magnetic properties can be substantially controlled by substitution concentration.     

Synthesis and characterization of Sr(ZnZr)x Fe12−2xO19-PANI composites

Strontium zinc zirconium hexaferrites/polyaniline (Sr(ZnZr)_xFe_12−2xO₁₉-PANI, x=0, 0.5, 1.0) composites were synthesized by oxidative chemical polymerization of aniline in the presence of ammonium peroxydisulfate (APS). The structure and morphology of the product was characterized by FTIR, TGA and SEM. The particle size of the core material was found to be about 250-500 nm. After coating with polyaniline, the particle size of Sr(ZnZr)_0.5Fe₁₁O₁₉-PANI composites grew upto 0.5-1.0 μm. XRD of the ferrites indicated that the structure of the core materials is hexagonal, with lattice constants around 5.886-5.885 Å. It was found that the saturation magnetization (M_S) and coercivity (H_C) for Sr(ZnZr)_xFe_12−2xO₁₉-PANI composites decreased after polyaniline coating. The composite under applied magnetic field, exhibited ferromagnetic hysteretic loops with high saturation magnetization (M_S=18.9-3.8 emu/g) and coercivity (H_C=3850.0-583.91 Oe).     

Sonochemical assisted synthesis of SrFe12O19 nanoparticles

We present the synthesis of M-type strontium hexaferrite by sonochemistry and annealing. The effects of the sonication time and thermal energy on the crystal structure and magnetic properties of the obtained powders are presented. Strontium hexagonal ferrite (SrFe₁₂O₁₉) was successfully prepared by the ultrasonic cavitation (sonochemistry) of a complexed polyol solution of metallic acetates and diethylene glycol. The obtained materials were subsequently annealed at temperatures from 300 to 900 °C. X-ray diffraction analysis shows that the sonochemical process yields an amorphous phase containing Fe³⁺, Fe²⁺ and Sr²⁺ ions. This amorphous phase transforms into an intermediate phase of maghemite (γ-Fe₂O₃) at 300 °C. At 500 °C, the intermediate species is converted to hematite (α-Fe₂O₃) by a topotactic transition. The final product of strontium hexaferrite (SrFe₁₂O₁₉) is generated at 800 °C. The obtained strontium hexaferrite shows a magnetization of 62.3 emu/g, which is consistent with pure hexaferrite obtained by other methods, and a coercivity of 6.25 kOe, which is higher than expected for this hexaferrite. The powder morphology is composed of aggregates of rounded particles with an average particle size of 60 nm.     

Physical and magnetic properties of highly aluminum doped strontium ferrite nanoparticles prepared by auto-combustion route

Highly Al³⁺ ion doped nanocrystalline SrFe_12−xAl_xO₁₉ (0≤x≤12), were prepared by the auto-combustion method and heat treated in air at 1100 °C for 12 h. The phase identification of the powders performed using x-ray diffraction show presence of high-purity hexaferrite phase and absence of any secondary phases. With Al³⁺ doping, the lattice parameters decrease due to smaller Al³⁺ ion replacing Fe³⁺ ions. Morphological analysis performed using transmission electron microscope show growth of needle shaped ferrites with high aspect ratio at Al³⁺ ion content exceeding x≥2. Al³⁺ substitution modifies saturation magnetization (M_S) and coercivity (H_C). The room temperature M_S values continuously reduced while H_C value increased to a maximum value of 18,100 Oe at x=4, which is an unprecedented increase (∼321%) in the coercivity as compared to pure Sr-Ferrite. However, at higher Al³⁺ content x>4, a decline in magnetization and coercivity has been observed. The magnetic results indicate that the best results for applications of this ferrite will be obtained with an iron deficiency in the stoichiometric formulation.     

Recent advances in processing and applications of microwave ferrites

Next generation magnetic microwave devices will be planar, smaller, weigh less, and perform well beyond the present state-of-the-art. For this to become a reality advances in ferrite materials must first be realized. These advances include self-bias magnetization, tunability of the magnetic anisotropy, low microwave loss, and volumetric and weight reduction. To achieve these goals one must turn to novel materials processing methods. Here, we review recent advances in the processing of microwave ferrites. Attention is paid to the processing of ferrite films by pulsed laser deposition, liquid phase epitaxy, spin spray ferrite plating, screen printing, and compaction of quasi-single crystals. Conventional and novel applications of ferrite materials, including microwave non-reciprocal passive devices, microwave signal processing, negative index metamaterial-based electronics, and electromagnetic interference suppression are discussed.     

Synthesis and magnetic properties of barium–calcium hexaferrite particles prepared by sol–gel and microemulsion techniques

The preparation of W-type hexaferrite particles with the composition BaCa₂Fe₁₆O₂₇ by microemulsion and a stearic acid sol–gel method with and without surfactant has been investigated at various sintering temperatures. The structural and magnetic characteristics have been studied by X-ray diffraction (XRD), a vibrating sample magnetometer (VSM), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), differential scanning calorimetric (DSC) and Fourier transform infrared (FTIR) techniques. The effect of sintering temperature on the properties of BaCa₂Fe₁₆O₂₇ hexaferrites has been studied. The value of saturation magnetization (M_s) depends on types of surfactant used. The sample prepared in the presence of polyoxyethylene (20) sorbitan monooleat (Tween 80) shows low saturation magnetization (M_s=15.10 emu/g), whereas the other sample prepared in the presence of a surfactant cetyltrimethylammonium bromide (CTAB) exhibits high saturation magnetization (M_s=24.60 emu/g) compared to the normal sample.