Ferrite BaFe12O19 Research Articles

Synthesis, physical and microwave absorption properties of Barium ferrite - P(VDF-TrFE) nanocomposites

We present results concerning the synthesis, magnetic, dielectric and microwave absorption properties of BaFe12O19 / P(VDF-TrFE) nanocomposites. First, barium ferrite nanopowders were prepared by the hydrothermal synthesis method. Structural and morphological properties of the prepared powders were investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM), showing as result a good quality spherical plus platelet-like shaped nanoparticles. Afterwards, composite films with filler nanoparticles of barium ferrite BaFe12O19 (BaFO, nominal 5-20 wt.%) dispersed within P(VDF-TrFE) acting as polymeric matrix have been prepared by solvent evaporation. Magnetic properties were examined by the vibrating sample magnetometry (VSM), and a direct comparison of results obtained for the composites respect to the pure nanopowder allow us to obtain the true nanofiller content value, different from the initially nominal one. Dielectric properties have been measured up to 2 MHz and show the typical behaviour of Maxwell-Wagner type interfacial polarization. From 10 kHz up, permittivity of the composites remains almost unchanged, with values that show a smooth increase as the %wt. of BaFe12O19 does. Finally, microwave absorption properties were analyzed by using ESR technique operating at X-band. All obtained results are discussed in terms of size and quantity of the composites BaFe12O19 filler nanoparticles.

Production of high-coercivity materials based on BaFe12O19 by crystallization of plasma-sputtered powders

Ferrite powders BaFe12O19 were studied in the present work after plasma heating and rapid quenching in differentenvironment: in air, in water and on the copper disk. X-ray diffraction analysis (XRD), scanning electron microscopy (SEM), vibration magnetometry (VSM) and Mossbauer spectroscopy (NGR) showed that the powder produced after quenching on the copper disk was in amorphous-crystalline state. The correlation between the annealing temperature and the value of magnetic parameters (coercive field and saturation magnetization) was established. Annealing at 1200 K for 2 h increases the coercive force up to 6.3 kOe. The processes of crystallization from the amorphous phase, that improve the magnetic properties of barium ferrite, are discussed.HighlightsWe studied the barium ferrite powdersafter plasma heating and rapid quenching.We studied the processes of crystallization from the amorphous phase.We studied theprocesses ofthermal annealing for the barium ferrite.

Magnetic, Micro-structural, and Optical Properties of Hexaferrite, BaFe12O19 Materials Synthesized by Salt Flux-Assisted Method

This paper reports the eco-friendly synthesized BaFe12O19 phase materials by a molten salt flux approach and their experimental findings. The reaction mixture (BaCO3 and Fe2 O 3) annealed with the mixture of salt (NaCl:KCl) flux yielded good quality nanocrystalline hexagonal ferrite BaFe12O19 phase materials. The plate-like hexagonal-shaped BaFe12O19 phase morphology with random particle sizes of ∼370 to 940 nm is seen for the good quality flux-annealed sample. The room-temperature magnetic hysteresis loop of the BaFe12O19 sample exhibits hard ferromagnetic saturation magnetization (M s) of 50.23 emu/g at 15 kOe, and coercive field (H c) is 3500 Oe. The determined energy bandgap (E g) is found to be 3.58 eV for the BaFe12O19 phase material. The Fourier transform infrared (FT-IR) spectral features confirm the presence of Fe–O and Ba–O bonds in the flux-synthesized BaFe12O19 materials. The photoluminescence (PL) emission peak (∼360 nm) intensity of BaFe12O19 materials varies regardless of annealing temperatures. The different salt flux-synthesized BaFe12O19 materials appear as brown- and dark gray-colored powders that can be applied as a ceramic color pigment due to its high NIR reflectivity.

Synthesis, structure and magnetic properties of hexagonal BaFe12O19 ferrite obtained via a hydrothermal method

Hexagonal M-type BaFe12O19 ferrites were synthesized via a hydrothermal method with Ba/Fe ratio from 1:12 to 1:7 in the raw materials, and their structure and magnetic properties are studied. When the Ba/Fe ratio is smaller than 1:9, the impurity α-Fe2O3 and BaFe2O4 can be found in the as-synthesized specimens, and it seems hard to avoid the formation of impurity BaCO3 during a hydrothermal process. The grain size of as-synthesized specimens decreases obviously with the increase of Ba/Fe ratio. The phase composition and morphology affect the magnetic properties of specimens markedly. In addition, it is found that the acid washing can improve the magnetic properties of specimens.

Simulation of Wasp-Waisted Magnetic Hysteresis Loop for NiCoP-Coated BaFe12O19–Polystyrene Bilayer Composite Film

Brillouin function was modified to model the wasp-waisted magnetic hysteresis loop for soft-magnetic NiCoP-coated hard-magnetic M-type ferrite BaFe12O19 polystyrene (PS) bilayer composite film taking into account the effective applied magnetic field due to localized impurity phases and significant change in the azimuthal angle of the magnetic moment due to the formation of bilayer structure of film by the addition of PS. It is shown that there is a good fit to the experimental data observed in wasp-waisted magnetic hysteresis loop. The analysis shows that the forward magnetization and reversal process are typical.

Microwave absorption performance enhanced by high-crystalline graphene and BaFe12O19 nanocomposites

The nanocomposites, consisting of BaFe12O19 ferrite and few-layer graphene sheets (FL-GSs) in various weight ratios (1−9 wt. %), were fabricated by a mechanical mixing method. The high-crystalline FL-GSs were prepared by direct current arc discharge evaporation of pure graphite electrodes in an H2–Ar gas mixture. We measured the electromagnetic properties, including effective magnetic permeability and effective permittivity in addition to microwave absorption performance, of the FL-GSs/BaFe12O19 nanocomposites compared with the pristine BaFe12O19 nanoparticles (NPs). The nanocomposite FL-GSs/BaFe12O19 with the optimal performance (6 wt. % FL-GSs) exhibited an effective microwave absorption (<−10 dB) bandwidth of 5.8 GHz with a thickness of 2.2 mm, 53% higher than that of the pristine BaFe12O19 NPs. Meanwhile, this nanocomposite had the minimum reflection loss of −49.7 dB at 8.4 GHz with a thickness of 2.8 mm, three times greater than those without FL-GSs. These performances result from a simultaneous increase in both magnetic and dielectric losses possibly due to synergistic effects of BaFe12O19 and FL-GSs. In such nanocomposites, both magnetic loss from BaFe12O19 and dielectric loss from FL-GSs contribute to the absorbing performances. Adding FL-GSs as dielectric fillers enhances the impedance matching of the nanocomposites compared with the pristine BaFe12O19 NPs based on the magnetic loss alone. Our results indicate that the incorporation of high-crystalline nanocarbon materials into ferrite oxides can provide high microwave absorption intensity and broad effective absorption bandwidth, while maintaining high thermal stability.

Strong coercivity reduction and high initial permeability in NiCoP coated BaFe12O19–polystyrene bilayer composite

Soft-magnetic NiCoP coated hard-magnetic M-type ferrite BaFe12O19 (BaM)–polystyrene (PS) bilayer composite film was successfully synthesized. X-ray diffraction peaks exhibited no change in the structure of BaM after coating with PS. The NiCoP coated BaM–PS composite exhibited a wasp-waisted magnetic hysteretic loop with remarkable reduction in the coercivity, remanence and squareness with respect to BaM–PS, which is useful for the core of a magnetic switching device to control currents so large that they are unmanageable. Moreover, the initial permeability measurement exhibits initial permeability of around 100 000 and thermal stability up to 558 K, which is good for flux-amplifying components of smaller inductors.

Magnetic Properties and Local Parameters of Crystal Structure for BaFe12O19 and SrFe12O19 Hexagonal Ferrites

Magnetic Properties and Local Parameters of Crystal Structure for BaFe12O19 and SrFe12O19 Hexagonal Ferrites

Synthesis of hexagonal BaFe12O19 and SrFe12O19 ferrite ceramics with Multiferroic Properties

The possibility of obtaining by ceramic technology barium and strontium hexagonal ferrites of the M type with multiferroic properties is considered. For the first time, samples of BaFe12O19 and BaFe12O19 with intense multiferroic properties at room temperature are obtained using a modified ceramic technology (particularly clean feedstock, B2O3 additives, sintering in an oxygen atmosphere). A comparison of the characteristics of the obtained multiferroic samples with the characteristics of the classical high-temperature multiferroic BiFeO3 as well as with the characteristics of ferrite ceramics BaFe12O19 and SrFe12O19 obtained by the technology of polymer precursors is performed. A mechanism to explain the properties of multiferroic hexagonal ferrite ceramic samples is proposed; the important practical significance of the results is noted.

Synthesis, physical and magnetic properties of BaFe12O19/P(VDF-TrFE) multifunctional composites

Composite films with filler microparticles of Barium ferrite BaFe12O19 (BaFO, 1–20wt.%) dispersed within P(VDF-TrFE) acting as piezoelectric polymeric matrix have been prepared by solvent evaporation. SEM and TEM images in combination with magnetic measurements clearly probe the good dispersion and random distribution of the BaFO microparticles within the films. Young’s modulus of the fabricated composites remains almost unchanged for all filler contents, indicating that this acts as a small defect within the P(VDF-TrFE) matrix. On the contrary, dielectric properties clearly reduce for low filler contents, 1 and 5wt.%, and recover and increase their values in a smooth and monotonous way for higher BaFO filler contents of 10 and 20wt.%. This trend is not followed by the electrical conductivity. Additionally, we have extended the study to fibers composed of BaFe12O19 microparticles within a PVDF matrix. Due to the big size of BaFO particles (about 1μm in diameter), a proper fabrication of the fiber shaped composites has not been achieved. We found that true BaFO content are always lower than nominal ones. Results are discussed in terms of the influence of size and morphology of the BaFO particles on the initial properties of the pure polymeric matrix.

Suppressing of slow magnetic relaxation in tetracoordinate Co(II) field-induced single-molecule magnet in hybrid material with ferromagnetic barium ferrite.

The novel field-induced single-molecule magnet based on a tetracoordinate mononuclear heteroleptic Co(II) complex involving two heterocyclic benzimidazole (bzi) and two thiocyanido ligands, [Co(bzi)2(NSC)2], (CoL4), was prepared and thoroughly characterized. The analysis of AC susceptibility data resulted in the spin reversal energy barrier U = 14.7 cm−1, which is in good agreement with theoretical prediction, Utheor. = 20.2 cm−1, based on axial zero-field splitting parameter D = −10.1 cm−1 fitted from DC magnetic data. Furthermore, mutual interactions between CoL4 and ferromagnetic barium ferrite BaFe12O19 (BaFeO) in hybrid materials resulted in suppressing of slow relaxation of magnetization in CoL4 for 1:2, 1:1 and 2:1 mass ratios of CoL4 and BaFeO despite the lack of strong magnetic interactions between two magnetic phases.

Magneto-optical studies of BaFe_12O_19 films grown by metallo-organic decomposition

M-type barium hexagonal ferrites BaFe12O19 (BaM) films considered for new devices that operate in the 40-70 GHz range with small or zero applied magnetic fields were characterized by magneto-optical (MO) complex polar “Kerr” effect (PKE) spectroscopy, MO magnetometry, and spectral ellipsometry (SE). The textured polycrystalline films were grown on Pt(111)/TiO2 template on Si wafer using metallo-organic decomposition technique (MOD) followed by rapid thermal annealing. In the films grown in one, two and three MOD iterations, the thickness was evaluated by SE and transmission electron microscopy. The film thickness ranged from 30 nm to 50 nm per MOD iteration. The best films display out-of-plane effective magnetic anisotropy field of 13 kOe, high perpendicular remanent magnetization and ferromagnetic resonance linewidth of 340 Oe at 60 GHz. The coercivity deduced from the MO hysteresis loops ranged between 0.25 kOe and 0.52 kOe. The SE and PKE spectra were taken at photon energies from 0.7 eV to 6.4 eV and from 1.2 eV to 4.8 eV, respectively. The PKE spectra display the structure observed on BaM single crystal natural faces normal to the c-axis. They are consistent with magnetoplumbite structure, with high degree of grain c-axis ordering, absence of foreign phases and Fe valence-exchange mechanism. Single phase nature of the films was further confirmed by grazing incidence X-ray diffraction and 57Fe nuclear magnetic resonance at 4.2 K.

Preparation and microwave-absorbing property of BaFe12O19 nanoparticles and BaFe12O19/Fe3C/CNTs composites

A novel kind of BaFe12O19/Fe3C/CNTs composite was developed by the acetylene chemical vapor deposition process. The composites perform great improvement in the microwave absorbing properties compared with pure BaFe12O19 ferrite in 2–18 GHz range.

Preparation and electromagnetic wave absorption hard–soft Ba ferrite/polypyrrole core–shell nanocomposites

The nanocomposite of hard (BaFe12O19)/soft ferrite was prepared, and then the polypyrrole (PPy)–BaFe12O19/Fe3O4 multi core–shell was produced by in situ polymerisation method. X-ray diffraction, transmission electron microscope, scanning electron microscopy and fourier transform infrared spectroscopy analysis indicated that Fe3O4 coated on the BaFe12O19 ferrite was homogenously enwrapped by PPy coating. The magnetic properties and electrical conductivity of the nanocomposite were characterised by vibrating sample magnetometer and four-wire technique respectively. As prepared conducting ferromagnetic polymer nanocomposites have electrical conductivity of the order of 5 S cm−1 and saturation magnetisation Ms value of 3 emu g−1. Microwave absorbing properties of the nanocomposite were investigated using vector network analysers in the frequency range of 8–12 GHz. The values of the minimum reflection loss were −23 dB at 10 GHz and −28 dB at 11·5 GHz for Fe3O4 coated on the BaFe12O19/Fe3O4/PPy core/shell nanocomposite with a thickness of 1·5 mm.

Liquid Phase Deposition of Barium Hexaferrite Thin Films

In this study we demonstrate for the first time that magnetic films with a complex crystal structure, such as hexagonal barium ferrite BaFe12O19, can be successfully fabricated in aqueous solutions at 60 °C by the liquid phase deposition method (LPD). Highly uniform films with a variable thickness were deposited on (001) Si substrates at 60 °C and analyzed by X-ray diffraction, scanning electron microscopy, Raman spectroscopy, and magnetic force microscopy. As expected, the as-deposited films are amorphous and consist of a mixture of metal oxide/oxyhydroxide intermediates which can be converted into the desired hexagonal barium ferrite phase upon heat treatment at 950 °C in air. The molar ratio of the metal cations in the treatment solution was found to play a crucial role on the composition of the films, with chemically pure BaFe12O19 films forming in solution when the Fe3+/Ba2+ molar ratio is n = 11. The films are constructed by close-packed spheroidal particles and have out-of-plane coercive fields whi...

Attractive microwave-absorbing properties of M-BaFe12O19 ferrite

BaFe12O19 ferrite was prepared at relatively lower calcined temperature (900°C) and assisted by reverse microemulsion technology. The as-prepared BaFe12O19 was characterized by X-ray powder diffractometer (XRD), Fourier transform infrared (FTIR) and thermogravimetric analyzer–differential scanning calorimeters (TGA–DSCs). The images of scanning electron microscopy (SEM) and transmission electron microscope (TEM) showed that the average size of sample was in the range of 130–160nm. The saturation magnetization and the coercivity of sample calcined at 900°C achieved 57.09emu/g and 4711Oe, respectively. When the thickness of the absorber coating was 2mm, the minimum value of reflection loss reached −28.52dB at about 13.80GHz, and available bandwidth was approximately 9.3GHz in the range of 8–18GHz. The as-prepared barium ferrite at relatively low temperature would be used as an advanced microwave absorption material.

A method for determining a uniaxial magnetic anisotropy constant of monodomain particles of powdered permanent magnets

A method for determining the uniaxial magnetic anisotropy constant of monodomain particles of powdered permanent magnets is based on the Mossbauer spectroscopy. The method is experimentally verified on a powdered permanent magnet made of barium ferrite BaFe12O19.

Effect of interface layer on dielectric and magnetic properties of 2–2 type Ba2Ti9O20–BaFe12O19 composite ceramics

2–2 type Ba2Ti9O20–BaFe12O19 composite ceramics were prepared by a tape casting method. Interface, dielectric and magnetic properties of prepared composite ceramics have been reported. Obvious interface diffusion between the dielectric and the ferrite has been observed by scanning electron microscopy and energy dispersive spectrometer. It was observed that the thickness of interface increased with increasing of sintering temperature. Compared with pure Ba2Ti9O20 ceramic, relatively high dielectric constant and loss of the prepared composite have been obtained. Meanwhile, lower saturation and remnant magnetizations, and higher coercive field than that of pure BaFe12O19 ferrite has also been obtained. The dielectric constant of the prepared composites increased and then decreased, with increasing of sintering temperature accompanied with an opposite variation for the dielectric loss. At the same time, the saturation magnetization, the remnant magnetization and the coercive field decreased.

Influence of BaTiO3 on the Structure and Magnetic Properties of Low- Temperature Sintered BaTiO3-BaFe12O19 Composites

In order to meet the requirements for low temperature co-fired ceramic devices at high frequency range, the sintering behavior, microstructure evolution, dielectric and magnetic properties of composites were investigated by varying the ratios of BaTiO3 to BaFe12O19 ferrite and additions of Bi2O3. In this paper, our results indicated that the BaTiO3 can adjust the structure and magnetic properties of the composites sintering at low temperature. Meanwhile, X-ray diffraction (XRD) and the scanning electron microscope (SEM) images showed that the composites were composed of BaTiO3 and barium ferrite. It can be seen that saturation magnetization decreased from 62 emu/g to 37.6 emu/g as the weight% varied from 0% to 15% and the samples with BaTiO3 had good dielectric properties in a wide frequency range. Ionic diffusion was found to take place between barium ferrites and BaTiO3, which contributed to the variety of the magnetic and dielectric properties observed in our samples.

Finite-size scaling relation of the Curie temperature in barium hexaferrite platelets

High-temperature magnetic measurements were carried out on barium ferrite BaFe12 O19 nanoparticles coated with amorphous silica. We find that the Curie temperature of this material decreases with decreasing particle size, in agreement with the finite-size scaling theory. In contrast to what one expects, the observed particle-size dependence of the Curie temperature does not follow a finite-size scaling relation for a zero-dimensional magnetic system. Instead, the data follow a finite-size scaling relation for a two-dimensional magnetic system with the scaling exponent ν = 0.78±0.06. The validity of the two-dimensional scaling relation in this material is due to the fact that the nanoparticles have a platelet-like shape.