BaFe12O19 Nanoparticles Research Articles

Synthesis of Electromagnetic Functionalized Barium Ferrite Nanoparticles Embedded in Polypyrrole

With flaky BaFe12O19 nanoparticles (BF NPs, 10-20 nm in thickness) as polymerization seeds, electromagnetic functionalized and microstructured quasi-spherical PPY/BF (PPY: polypyrrole) organic-inorganic composites were prepared by a conventional in situ chemical oxidative polymerization. X-ray diffraction and Fourier transform infrared analyses interpreted that there was no obvious chemical interaction between BF NPs and PPY in the composites but that BF NPs only served as the nucleation sites for the polymerization of pyrrole. As compared to pure BF NPs, PPY/BF composites showed distinct increases in electrical conductivities and decreases in magnetization and thus improved the matched characteristic impedance of the free space, leading to a substantial enhancement of reflection loss at 2-18 GHz. For the first time, multi-layered and single-layered films formed at different places on the reaction flask were studied by scanning electron microscopy and energy dispersive X-ray analysis, indicating that the films composed of quasi-spherical microstructures can be very different in morphology but surprisingly contain no BF NPs.

Synthesis and Electro-magnetic Properties of Polyaniline-barium Ferrite Nanocomposite

The polyaniline (PANI)-barium ferrite composite with magnetic behavior was synthesized by in situ polymerization of aniline in the presence of BaFe12O19 nanoparticles of 6080 nm in diameters. The structure, morphology and magnetic properties of samples were characterized by powder X-ray diffraction, Fourier transform infrared, scanning electron microscopy, transmission electron microscopy and vibrating sample magnetometer technique. The results of spectroanalysis indicated that there was interaction between PANI chains and ferrite particles. The composite exhibited the hysteresis loops of the ferromagnetic nature. The saturated magnetization of composite was 22.2 emu/g and the conductance was 0.069 S/cm.

Effect of stoichiometry on the phase formation and magnetic properties of BaFe12O19 nanoparticles by reverse micelle technique

Structure parameters and field-dependent magnetic properties of BaFe12O19 nanoparticles synthesized from different Fe/Ba ratios by reverse micelle technique were investigated. Pure barium ferrite phase and best magnetic properties could be obtained for the sample prepared from Fe/Ba ratio of 11, with grain size in the range of 20–30 nm as shown by TEM. The existence of α-Fe2O3 in other materials obviously decreases the magnetization properties, but coercivities of the materials from Fe/Ba ratio of 9.5 and 10 are abnormally even higher than the prepared pure BaFe12O19. The abnormal high coercivities of some prepared materials were explained from anisotropy mechanisms of nanoparticles.

Synthesis and Characterization of Novel Coralloid Polyaniline/BaFe12O19 Nanocomposites

By supplying inorganic ferrite nanoparticles of different morphologies as nucleation sites, PANI/ferrite nanocomposites with novel coralloid structures were synthesized successfully through a simple, conventional, and inexpensive one-step in situ polymerization method without the aid of any surfactant, organic dopant, or template. As shown by XRD, FT-IR and UV−vis, there is no obvious chemical interaction between PANI and BaFe12O19 (BF) nanoparticles; that is, ferrite nanoparticles served only as the nucleation centers for the growth of PANI nanofibers, whereas the nanoparticles have an effect in reducing the diameters of the produced PANI nanofibers. PANI/BF nanocomposites are hard magnetic properties with alternative electrical conductivities and magnetic properties. The reflection loss of BF nanoparticles in 2−18 GHz was essentially enhanced upon PANI coating, and the frequency relating to maximum reflection loss shifts to a higher value with the increase in BF content because of the higher anisotropy ...

Hydrothermal Synthesis of Ba‐Hexaferrite Nanoparticles

Barium hexaferrite BaFe12O19 nanoparticles with a single‐domain size were synthesized using a controlled hydrothermal process involving the LaMer–Dinger principle and the Ostwald ripening mechanism. Nanocrystalline particles of BaFe12O19 were obtained when the molar ratio of the precursor composition Ba(OH)2·8H2O/γ‐Fe2O3 was 0.3 and the concentration of the suspension was about 1 wt%. The as‐synthesized crystalline BaFe12O19 platelets approximately 50 nm in length and 5 nm in thickness exhibited a saturation magnetization of 40 Am2/kg.

Synthesis of nonstoichiometric M-type barium ferrite nanobelt by spark plasma sintering method

This study investigated the feasibility of ultrafast crystallization of M-type barium ferrite when the coprecipitation precursors in stoichiometric proportions as BaFe12O19, Fe(OH)3 and BaCO3 nanoparticles, had been heated by spark plasma sintering (SPS) process. The results show that SPS method may realize the ultrafast crystallization of M-type barium ferrite, absolutely prevent the crystallization of intermediate phase α-Fe2O3, and significantly decrease the crystallization temperature of M-type barium ferrite. The sintered samples obtained at 800 °C by sintering the precursors for 10 minutes are a kind of multiphase ferrites composed of major phase M-type barium ferrite and trace amount of BaFe0.24Fe0.76O2.88. It is discovered that M-type barium ferrites in the holes of the sintered samples are in nanobelt microstructure about 100–300 nm in width and several micrometers in length. These M-type barium ferrite nanobelts are non-stoichiometric and may be expressed as BaFe12+xO19+1.5x (−4.77⩽x⩽6.50). Their composistions suggest completely random Fe-rich or Ba-rich domains.

Preparation and thermal behavior of aerosol-derived BaFe12O19 nanoparticles

Pure BaFe12O19 nanoparticles, having single magnetic domain sizes, were obtained at 700°C using a process combining the citrate precursor method and spray technique. A neutralized aqueous solution, containing Ba2+ and Fe3+ chelated by citric acid, was nebulized to undergo thermal decomposition in a flowing air with a maximum temperature of 250°C. The dried solid precursor so obtained was calcined at different temperatures and was then chemically and physically characterized. Crystalline barium hexaferrites were formed at temperatures as low as 650°C, but calcination temperatures higher than 680°C were required to produce pure barium ferrite powder. Based on the obtained experimental results, the reaction mechanism for the aerosol-derived precursor to form BaFe12O19 was proposed and discussed in this study.

Magnetic properties in BaFe12O19 nanoparticles prepared under a magnetic field

It was observed that the nanocrystallites of BaFe12O19 formed at 140°C under a 0.25T magnetic field exhibited a higher saturation magnetization (6.1emu/g at room temperature) than that of the sample (1.1emu/g) obtained under zero magnetic field. Both of the two approaches yielded plain-like particles with an average particle size of 12nm. However, the Curie temperature (Tc), a direct measuring of the strength of superexchange interaction of Fe3+–O2−–Fe3+, increased from 410°C for the nanoparticles prepared without an external field applied to 452°C for the particles formed under a 0.25T magnetic field, which indicates that external magnetic fields can improve the occupancy of magnetic ions and then increase the superexchange interaction. This was confirmed by electron paramagnetic resonance and Mössbauer spectrum analysis. The results present in this paper suggest that in addition to oxygen defects, surface non-magnetic layer and a fraction of finer particles in the superparamagnetic range, cation vacancies should be responsible for the decreasing of saturation magnetization in magnetic nanoparticles.

Electron paramagnetic resonance of ferrite nanoparticles

Three types of iron-based oxide nanoparticles (weight compositions Fe2O3, BaFe2O4, and BaFe12O19) embedded in a polyethylene matrix are studied using the electron paramagnetic resonance technique. All nanoparticles are found to be multiphase. Thermal variations of electron paramagnetic resonance spectra reveal the presence of two phases in the Fe2O3 nanoparticles. One such phase undergoes an antiferromagnetic-like transition near 6 K. Nanoparticles of BaFe2O4 demonstrate a resonance anomaly near 125 K that could indicate the presence of a magnetic phase. Reduced magnetic anisotropy in BaFe12O19 nanoparticles may be related to either structural imperfection or particle smallness (effective diameter of less than 10 nm). Our data clearly show that low temperature experiments are desirable for the correct identification of nanoparticles by means of the electron paramagnetic resonance technique.

Olympic Ring Formation from Newly Prepared Barium Hexaferrite Nanoparticle Suspension

We report here, the first observation of features such as the Olympic Rings on transmission electron micrographs of amorphous BaFe12O19 nanoparticles prepared by a sonochemical decomposition technique. The barium hexaferrite was formed as a colloidal solution without the use of a surfactant. Rings of smaller dimensions trapped inside the larger ones was another unique observation. The intersection of two rings is amazing, as this is in direct contradiction to the proposed mechanism for the ring formation, based on the dry hole formation on an evaporating thin film completely wetted to the substrate. The creation of this unique feature is attributed to the interplay of magnetic forces with the regular particle−substrate interactions.