Nanocrystalline Barium Hexaferrite Research Articles

Synthesis and properties of nickel-doped nanocrystalline barium hexaferrite ceramic materials

M-type barium hexaferrite ceramics have emerged as important materials both for technological and commercial applications. However, limited work has been reported regarding the investigation of nanocrystalline Ni-doped barium hexaferrites. In this study, nanocrystalline barium hexaferrite ceramics with the composition BaFe12−xNi x O19 (where x = 0, 0.3 and 0.5) were synthesized by sol–gel method and characterized using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, vibrating sample magnetometer and precision impedance analyzer. All the synthesized samples had single magnetoplumbite phase having space group P63/mmc showing the successful substitution of Ni in BaFe12O19 without the formation of any impurity phase. Average grain size of undoped samples was around 120 nm which increased slightly with the addition of Ni. Saturation magnetization (Ms) and remnant magnetization (Mr) increased with the addition of Ni, however, coercivity (Hc) decreased with the increase in Ni from x = 0 to x = 0.5. Real and imaginary parts of permittivity decreased with the increasing frequency and increased with Ni content. Dielectric loss and conductivity showed slight variation with the increase in Ni concentration.

Erratum: “Synthesis of nano-crystalline barium hexaferrite in the presence of salt catalysts”

Erratum: “Synthesis of nano-crystalline barium hexaferrite in the presence of salt catalysts”

Erratum: “Effects of process control agents on the synthesis of nano-crystalline barium hexaferrite”

Nano size particles of barium hexaferrite were produced by conventional mixed oxide ceramic method from BaCO3 and αFe2O3 as starting materials with a Fe/Ba molar ratio of 11. The mixture of precursors was intensively milled by high energy ball mill and the The influence of various process control agents (PCA) on the process has been investigated. Analysis of the XRD patterns indicates that PCA can strongly alter the morphology and phase composition of ball milled powder particles. In all milled samples, BaCO3 completely decomposed and slight displacement of reflections of hematite phase due to the dissolving of various ions like Ba or C in its lattice is observed. Nano size particles exhibiting angular shape together with some amorphous structure were observed in the sample processed in the presence of NaCl. Barium hexaferrite magnetic phase was partially formed in sample milled in the presence of stearic acid.

Electromagnetic interference shielding properties of nanocomposites for commercial electronic devices

A novel functional nanocomposites microwave shielding material using natural rubber (NR) loaded with binary active fillers barium hexaferrite (BF) (BaFe12O19) and carbon nanoparticle (CB) were fabricated by conventional roll milling technique. Nanocrystalline barium hexaferrite with particle size of 16 nm were successfully synthesized by hydrothermal approach at low temperature. The surface morphology of the nanocomposites was investigated using X-ray, field emission scanning electron microscopy and transmission electron microscopy. The electrical resistivity of the nanocomposites is decreased with BF loading level. The dielectric constant of the composites is decreased with increasing microwave frequency. NR/BF nanocomposites were screened for electromagnetic interference (EMI) shielding effectiveness (SE) over a frequency band of 1---12 GHz. A maximum SE value is approximately 75 dB in the frequency range of 1---12 GHz for BF content of 20 wt % and thickness of 1 mm. An excellent agreement between the theoretically predicted SE and the measured data was found. These features collectively demonstrated the potential of NR/BF nanocomposites for versatile applications in microwave shielding application and commercial electronic devices issues.

Acetone and ethanol sensing of barium hexaferrite particles: A case study considering the possibilities of non-conventional hexaferrite sensor

Hexaferrites are well known for their important magnetic and data storage applications. The volatile organic compound (VOC) sensing of hexaferrites is not reported yet in open literature. In the present work, acetone and ethanol sensing characteristics of nano-crystalline barium hexaferrite particles has been investigated. The phase formation behaviour and microstructure evolution of the synthesized barium hexaferrite particles are studied using X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM) techniques. Ultraviolet–visible (UV–vis) absorption and current–voltage studies are carried out to confirm the semiconducting nature of the particles. Gas sensing study revealed barium hexaferrite as promising sensor for the fast and reproducible detection of acetone and ethanol vapours at low concentrations (20ppm). The present systematic study on the promising acetone and ethanol sensing characteristics of barium hexaferrite particles could play significant role to explore the possibilities of non-conventional hexagonal ferrite sensors.

Synthesis and Characterization of Porous Nano-Crystalline Barium Hexaferrite

Barium hexaferrite/high density polyethylene composite was prepared from synthesized barium hexaferrite as matrix with 0, 10, 20, 30, 40 wt.% of high density polyethylene via a high energy planetary ball milling for 10 h. The milling products were isostatically pressed and finally sintered at 1250 °C for 1 h. Effect of HDPE content on morphology of the products were investigated using scanning electron microscope (SEM). Vibrating samplemagnetometer (VSM) analysis of single phase BaFe12O19 indicates saturation magnetization and coercivity of 52 emu/g and 4300 Oe, respectively. Visually, as the weight percent of the HDPE increases, more porous structure was observed. Moreover, the density of the sintered sampleslinearly decreased from 4.16 to 1.41 g/cm3 by increasing the amount of HDPE from 0 to 40 wt.%.

Arsenic removal by magnetic nanocrystalline barium hexaferrite

Nanoscale magnetite (Fe3O4) ( 200 nm assemblies. By using BHF, we demonstrate that nanoparticle removal is more efficient and fixed bed type cartridge applications are more possible.

Magnetic Properties of Nanocrystalline Barium Hexaferrite Thin Films Prepared by Sol-Gel Method

Single-phase nanocrystalline BaFe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">19</sub> thin films have been prepared on Si (110) substrates by sol-gel method. The efforts have been done to reduce the crystallite size of the single-phase barium hexaferrite thin films in order to develop the thin films for high-density magnetic recording media. Precursor solutions were primed with various Fe/Ba ratios and two kinds of basic agents. Then the coated films were heat treated at different temperatures. The effects of calcination temperature, molar ratio of Fe/Ba, and basic agent on phase composition, crystallites size, morphology, and magnetic properties were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), and vibrating sample magnetometery (VSM) techniques. The results showed that the lowest calcination temperature for production of the single-phase barium hexaferrite thin film by sol-gel method was 700degC. This product exhibited a nanostructure with high in-plane coercivity.

Influence of Fe/Ba ratio, basic agent and calcination temperature on the physical properties of nanocrystalline barium hexaferrite thin films prepared by a sol–gel method

In this work nanocrystalline BaFe 12 O 19 thin films have been prepared on the Si (1 1 0) substrates by a sol–gel method using the aqueous solution of metal nitrates. The efforts have been done to decrease the calcination temperature and to reduce the crystallite size of the single-phase barium ferrite thin films. The precursor solutions were primed with the various Fe/Ba ratios and two kinds of the basic agents, and the coated films were heat treated at the different temperatures. The thin films were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM) techniques. The effects of calcination temperature, molar ratio of Fe/Ba and basic agent on composition, crystallites size and morphology were also investigated.

A Comparative Study on the Morphology and Magnetic Properties of Barium and Strontium Hexaferrite Nanoparticles Synthesized by Co-Precipitation Method

Nanocrystalline strontium hexaferrite (SrFe12O19) and barium hexaferrite (BaFe12O19) powders were synthesized by co-precipitation method. The ‘as synthesized’ powders were heat treated (HT) at different temperatures ranging from 800 to 1200°C at a heating rate of 30°C /min in nitrogen atmosphere. Decomposition behaviour and the phases associated therein are investigated by thermal analysis (DTA/DTG/TG) and X-ray diffraction (XRD). Formations of ultrafine particles have been confirmed through field emission scanning electron microscop (FESEM). The superparamagnetic behavior of both, barium and strontium hexaferrite is confirmed by vibrating sample magnetometer (VSM). The increase in saturation magnetization from 1.94 to 31.05 emu/gm in case of barium hexaferrite and from 2.44 to 43.38 emu/gm for strontium hexaferrite is observed with HT temperatures. The changes in coercivity and remanence with HT temperatures for both the ferrites are analysed.

Synthesis of Nano-Crystalline Barium Hexaferrite Using a Reactive Co-Precipitated Precursor

Nano-crystalline particles of barium hexaferrite have been prepared by co-precipitation route using solution of iron and barium chlorides with a Fe/Ba molar ratio of 12 by addition of NaOH with OH-/Cl- molar ratio of 2. A mixture of water and diethylene glycol with volume ratio of 1:3 was used as a solvent in the process. Dried co-precipitated powder was annealed at various temperatures for 1 h. FTIR, XRD, DTA/TGA, SEM, and TEM techniques were used to evaluate powder particle characteristics. DTA/TGA results confirmed by those obtained from XRD indicated that the formation of barium hexaferrite occurs at relatively low temperature of 614 degC for precursor synthesized in diethylene glycol/water solution. The corresponding mean crystallite size measured by TEM for sample annealed at 700degC was 35 nm.

SYNTHESIS OF NANO CRYSTALLINE BARIUM HEXAFERRITE IN THE PRESENCE OF SALT CATALYSTS

Nano crystalline barium hexaferrite, BaFe 12 O 19, were synthesized from mixture of barium acetate and iron oxide by conventional mixed oxide ceramic method. The mixture of precursors together with a 3wt% salt-catalyst (ammonium and sodium chlorides) was intensively milled by high energy ball mill for 10 hr. The influence of addition of catalyst on the synthesis process has been studied by XRD, SEM, DTA/TG and TEM techniques. Analysis of the XRD patterns indicates that salt-catalysts can strongly alter the morphology and phase composition of ball milled powder particles. Sample with 3wt% NH 4 Cl after milling for 10 hr and annealing at 900°C for 1 hr exhibited single phase barium hexaferrite with mean crystallite size of 20 nm.

EFFECTS OF PROCESSING CONDITIONS ON THE CHARACTERISTICS OF NANO-CRYSTALLINE BARIUM HEXAFERRITE PREPARED BY MECHANICAL ALLOYING METHOD

In this research, the effect of milling time and annealing temperature on a heat activated synthesis of barium hexaferrite from mechanically activated mixture of hematite and barium acetate was investigated. The properties of samples were examined by XRD, DTA/TGA, SEM and VSM methods. The initial mixture with Fe / Ba molar ratio of 11 was milled for 24–48 h and then annealed at 800–1100°C. The XRD results showed the reflections of hematite as a major phase and barium hydroxide as a minor phase during mechanical milling in all three samples. It was observed that the specimen milled for 48 h exhibits the smallest mean crystallite size of 25 nm for hematite, as major phase. XRD results showed that annealing at 1100°C produces more pure barium hexaferrite phase comparing to lower temperatures. So, it was concluded that single phase BaFe 12 O 19 can be achieved by milling for 48 h and then annealing at 1100°C. The sample processed at these conditions exhibited nano-crystalline barium hexaferrite powders with a mean crystallite size of 46 nm, mean particle size of about 200 nm and high coercivity of 334.2 kA/m.

Nano-Crystalline Barium Hexaferrite Powders Prepared by Mechanical Alloying Using Acetate Precursor

Nano-crystalline barium hexaferrite powders have been prepared by mechanical alloying of nFe2O3+Ba(CH3COO)2 with Fe/Ba molar ratios of 10-12 and subsequent heat treatment. Thermal behavior, phase composition, morphology and magnetic properties of samples were studied using DTA/TGA, XRD, SEM and VSM, respectively. Nano-crystalline Ba-hexaferrite with a mean crystallite size of 46 nm and magnetic properties as high as Ms = 73.9 A.m2/kg and Hci = 334.2 kA/m was formed for mixture of 5.5Fe2O3+Ba(CH3COO)2 which was milled for 48 h and then annealed at 1100 °C.

RETRACTED: Effect of Fe/Ba mole ratios and surface-active agents on the formation and magnetic properties of co-precipitated barium hexaferrite

Nanocrystalline barium hexaferrite (BaFe 12O 19) powders have been synthesized through the co-precipitation route. The produced ferrite precursors were obtained from aqueous mixtures of barium and ferric chlorides by co-precipitation of barium and iron ions using 5 M sodium hydroxide solution at pH 10 in room temperature. These precursors were calcined at temperatures of 800–1200 °C for constant 2 h in a static air atmosphere. The effect of Fe 3+/Ba 2+ mole ratio and addition of surface-active agents during co-precipitation step on the crystal structure, morphology and magnetic properties of produced ferrite powders were studied. The results obtained showed that the single phase BaFe 12O 19 powders was achieved by decreasing the Fe 3+/Ba 2+ molar ratio from the stoichiometric value 12 to 8 and increasing the calcination temperature ≥1000 °C. In addition, the Fe 3+/Ba 2+ mole ratio of 8 and presence of surface-active agents promoted the formation of homogeneous nanopowders (ca. 113 nm) of BaFe 12O 19 at a low temperature of 800 °C with good saturation magnetization (50.02 emu/g) and wide coercivities (642.4–4580 Oe).

Synthesis and characterization of barium hexaferrite nanoparticles

This investigation dealt with the synthesis of nanocrystalline barium hexaferrite (BaFe 12O 19) powders through the co-precipitation–calcination route. The ferrite precursors were obtained from aqueous mixtures of barium and ferric chlorides by co-precipitation of barium and iron ions using 5 M sodium hydroxide solution at pH 10 in room temperature. These precursors were calcined at temperatures of 800–1200 °C for constant 2 h in a static air atmosphere. The effect of Fe 3+/Ba 2+ mole ratio and addition of surface active agents during co-precipitation step on the structural and magnetic properties of produced ferrite powders were studied. It is found that the formation of single phase BaFe 12O 19 powders was achieved by decreasing the Fe 3+/Ba 2+ molar ratio from the stoichiometric value 12–8 and increasing the calcination temperature ≥1000 °C. In addition, the Fe 3+/Ba 2+ mole ratio of 8 the surface active agents promoted the formation of homogeneous nanopowders (ca. 113 nm) of BaFe 12O 19 at a low-temperature of 800 °C with resultant good magnetic saturations (50.02 emu/g) and wide intrinsic coercivities (642.4–4580 Oe).

Determination of the Surface Anisotropy Contribution to the Magnetic Anisotropy Field of a Nanocrystalline Barium Ferrite Powder at Various Temperatures

The temperature dependence of the average anisotropy field of a nanocrystalline barium hexaferrite powder was studied by treating remanent-magnetization curves with inclusion of thermal fluctuations. The contribution of surface anisotropy was isolated; its nonstandard temperature dependence is intimately related to the specific features of formation of near-surface regions in ultrathin particles.

Glassy behavior in magnetic fine particles

A detailed study of the static and dynamic magnetic properties of nanocrystalline barium hexaferrite powder was done. Particles of about 10 nm diameter exhibit the main features attributed to glassy behavior. Different results make evident the presence of strong interactions in the studied system. This glassy state is mostly attributed to the frustration induced by magnetic interactions between randomly distributed particles, although the surface spins contribution cannot be discarded. The effective energy barrier distribution obtained from the analysis of the time dependence of the thermoremanence in terms of the T ln ( t/ τ 0) scaling shows a maximum located at energies higher than the mean anisotropy energy barrier. When doing the relaxation experiments after field cooling at increasing fields, the obtained effective energy distribution progressively resembles the anisotropy energy distribution. Therefore, we demonstrate how the glassy state can be erased by applying a magnetic field.

Preparation of nanocrystalline barium hexaferrite in a glass medium

Barium hexaferrite phase of composition BaO-6Fe 2O 3 of dimensions in the range 8.2 to 17.6 nm have been grown within a glass medium by subjecting the latter to a suitable heat treatment. Magnetization measurements on the resultant glass-ceramic have been carried out at temperatures varying from 20 to 300 K. The coercive field H c is found to be much smaller than that of bulk hexaferrite. The value of H c increases as the temperature is reduced. Also, H c shows an increase with the increase of hexaferrite particle size. It appears that the effective anisotropy constant plays an important role in determining this behavior.

Determination of anisotropy fields in magnetic particle systems. Application to bariumhexaferrite powders

A theory is set up to calculate anisotropy fields in assemblies of fine magnetic particles from remanence curves. The formalism takes into account the effects of thermal fluctuations. With the help of this approach anisotropy fields of microcrystalline and nanocrystalline bariumhexaferrite particles are determined. >