Barium Ferrite Powders Research Articles

An ultrafine barium ferrite powder of high coercivity from water-in-oil microemulsion

An ultrafine barium ferrite powder of high coercivity and high saturation magnetization has been successfully prepared from an inverse water-in-oil microemulsion consisting of cyclohexane, NP5/NP9, and an aqueous solution of mixed ferric nitrate and barium nitrate. An ammonium hydroxide solution was used as the precipitant to obtain the hydroxide precursor of particle size in the range of 10–30 nm from the microemulsion. The resulting precursor is characterized using techniques such as thermogravimetric analysis (TGA), differential thermal analysis (DTA) and a FT-IR analyzer. It was then calcined at various temperatures ranging from 600 to 950°C in order to develop the designed barium ferrite phase. Phase development in the precursor at each calcination temperature was monitored using X-ray diffractometer and a 57Fe-Mössbauer spectrometer analyzer. The particle size and size distribution of the calcined powders were determined using light scattering technique, scanning electron microscope and a transmission electron microscope. A high purity barium ferrite was obtained when the precursor was calcined at 950°C for 4 h. It exhibits an intrinsic coercivity ( i H c) of 5639 Oe and a saturation magnetization ( M s) of 69.7 emu/g, when characterized using a vibrating sample magnetometer (VSM).

Key step in synthesis of ultrafine BaFe12O19 by sol-gel technique

Barium hexaferrite powders have been prepared by sol-gel technique. Different ways in heat treatment of the gel are adopted to study the factors that influence the formation mechanism, morphology and magnetic properties of BaFe12O19. Results show that preheating the gel between 400 and 500°C for several hours is a key step, it can prevent the formation of α-Fe2O3 intermediate and obtain ultrafine BaFe12O19 single phase with improved magnetic properties and narrow size distribution at a low temperature. The barium ferrite powder had a coercive force of 5950 Oe and a magnetization of 70 emu/g, both are in good agreement with the expected values theoretically.

Preparation of Single Crystallites of Barium Ferrite by Hydrothermal Synthesis

We investigated the formation process and characteristics of barium ferrite single crystallite prepared by hydrothermal synthesis and the effect of heat treatment on crystallization and magnetic properties. The single phase of barium ferrite is formed in the batch composition Ba:Fe 1:10 and above alkali molar ratio 2.5. The particle size has tendency to decrease with increase in alkali molar ratio. Crystallization and magnetic properties of the hydrothermal-synthesized barium ferrite powders can be improved by the heat treatment.

The preparation of barium ferrite nanocrystalline powders by a stearic acid gel method

A new stearic acid gel method has been shown to be suitable for preparing BaFe 12O 19 nanostructured powders with narrow particle size distribution. Each state of the synthetic process was followed by use of DTA, TG, IR and X-ray analysis. The particle size and morphology were determined by transmission electron microscopy. The chemical composition of these particles was consistent with that of the stoichiometric bulk material analyzed by ion emission spectroscopy. Using this method, smaller, uniform-size and high purity BaFe 12O 19 nanocrystals could be easily obtained.

Radiothermal synthesis of fine barium ferrite powders and their properties

Ultrathin Ba ferrite particles have been synthesized using the melt coprecipitation method with elements of radiation technology. The discrepancy found between magnetization in fields H > H a and cation distribution data is explained within the model of particles nonuniformly magnetized over the bulk.

Synthesis of substituted M- and W-type barium ferrite nanostructured powders by stearic acid gel method

A series of substituted barium ferrites of M-type, Ba(CoTi) x Fe 12−2 x O 19, and W-type, BaZn 2− y Co y Fe 16O 27, were prepared as nanostructured powders using the stearic acid gel method. Well-crystallized nanocrystalline hexaferrite particles of 10–20 nm have been obtained at temperatures 650–750°C lower than those of other methods. The structures and micrographs of the nanocrystalline materials were characterized by X-ray diffraction and transmission electron microscopy. The phase composition of the intermediate products during the synthesis has been investigated by differential thermal analysis, thermogravimetric analysis, IR spectroscopy and X-ray analysis.

Thermally activated crystalline phase restoration in disordered barium ferrite powder prepared by ball milling

Depending on milling conditions (air or vacuum) for the same milling time, a different level of decomposition and structure disorder in BaFe12O19 ferrite powders can be obtained by ball milling. Air-milled material has a tendency to form a gas-saturated disordered structure (superoxide) and to transform into simple oxides (reduction process through oxygen-saturated disordered phase) as opposed to the vacuum-milled powder where a highly disordered phase occurs. Both powders have a different morphology (particle size and distribution). Annealing processes produce crystalline barium ferrite phase with interesting magnetic properties, but in the present paper only structural transformations are analysed. Scanning electron microscopy, X-ray diffraction and thermal analysis techniques were applied to study the effects of heat treatment (10 h at 773 or 1273 K) in disordered BaFe12O19 ferrite powders prepared by 1000 h ball milling in air and vacuum.

Barium ferrite powders as magnetic components of rectal suppositories

Barium ferrite powders as magnetic components of rectal suppositories

The effect of the molar ratio of cations and citric acid on the synthesis of barium ferrite using a citrate process

A model is presented to evaluate the concentration of species in a citric solution for preparing barium ferrite powder. The evaluated concentration of species provides valuable information and help in selecting the optimal condition for preparation of the barium ferrite powder using the citrate process. The influence of the molar ratio of cations and citric acid on the formation of barium ferrite is studied. The formation temperature of barium ferrite decreases as the ratio increases. When the molar ratio of cations and citric acid is 13∶20, the barium ferrite can completely form at 700 °C.

Transverse susceptibility of particulate recording media in different remanence states

Transverse susceptibility measurements were performed on isotropic and aligned γ-Fe2O3 and ZnTi-doped barium-ferrite powder samples in different remanence states. Measurement results obtained on a sintered NdFeB sample are given for comparison. Deviations of the experimental result from the Stoner–Wohlfarth theory are ascribed to inhomogeneous magnetization states and particle–particle interactions. The remanent reversible transverse susceptibility appears to be much more sensitive to these influences than standard remanence-curve analysis and thus provides a new experimental approach to the interaction problem.

Effect of ferrite powder fineness on the structure and properties of ceramic materials

Comprehensive study of the structure and properties of ferrite materials prepared from powders with different specific surface (0.4 m2/g<Ssp<1.2 m2/g) shows that the optimum specific surface of manganese—zinc ferrite powders is about 0.6 m2/g. With an increase in the specific surface of nickel—zinc and barium ferrite powders the porous crystalline structure of sintered specimens and most of the main electromagnetic properties of ferrite articles are improved.

Preparation of high-coercivity fine barium ferrite powder

The structural and magnetic properties of the thermally activated transformation from nanostructural material, mechanically disordered and decomposed BaFe12O19 ferrite powder to pure crystalline phase, have been studied by x-ray diffraction, scanning electron microscopy, and vibrating sample magnetometry analysis techniques. All experiments were performed on as-milled (1000 h) in air, and in vacuum and annealed Ba-ferrite samples (4 h at 773 and 1273 K). In parallel with the structure and particle morphology changes, we investigate the influence of heat treatment on the powder M-H hysteresis parameters in relation to the preparation routes, i.e., powder obtained by ball milling in air and vacuum, and annealed in air or vacuum.

Magnetic properties of substituted barium ferrite powders

Hexagonal barium ferrites were prepared using the citrate method. Cobalt and titanium were added in the amounts x from 0.2 to 1.1 ion /f.u. related to the formula BaCo/sub x/Ti/sub x/Fe/sub 12-2x/O/sub 19/. The heat treatment has been applied in three steps of 550/spl deg/C/5 hrs, 850/spl deg/C/2 hrs and 1100/spl deg/C/2 hrs. The following magnetic properties have been achieved: H/sub c//spl sim/80 kA/m, J/sub s/-120/spl times/10/sup -6/Tkg/sup -1/m/sup 3/, and J/sub r/-60/spl times/10/sup -6/ Tkg/sup -1/m/sup 3/ in the composition for which x is equal to 0.5 ion/f.u. The magnetic parameters have been measured by the vibration magnetometer. >

Hexaferrite particles prepared by a novel flux method with δ-FeOOH as a precursor

δ-FeOOH precursor, precipitated by NaOH from an aqueous solution containing both barium and ferrous ions, was used to grow barium and strontium ferrites in a flux of NaCl. Differential thermal analysis, thermo-electrical analysis and magnetic measurements were employed to study the formation of barium ferrite (BF). Fe M (M = Ba or Sr) ratios of 8–10 and flux ratios ( Na Fe ) of 3.5–7 were found to be optimal. BF formation starts at temperatures as low as 600 °C and has a greatly enhanced reaction rate at elevated temperatures; both observations are attributed to the use of δ-FeOOH precursor. Doping of (Co,Ti) or (Zn,Ti) in place of Fe is possible in this technique and leads to reduced particle size and coercivity. Hence the modified barium and strontium ferrite particles have coercivities of 600–2000 Oe, and saturation and residual magnetizations of 57–67 and 24–29 emu g −1, respectively; the particles are 30–200 nm in size, with a fine platelet shape. They are thus potential candidates as high-density recording media. This novel method provides a more economical and less polluting way to mass produce barium (strontium) ferrite powders for recording purposes.

Temperature dependence of the magnetization in fine particle systems and the Hopkinson effect. Application to barium ferrite powders

The dependence of the magnetization of particle assemblies on the magnetic field and the temperature is determined theoretically. We confine ourselves to small fields for simplicity. The magnetization shows a peak just below the Curie temperature T c when heating the system (Hopkinson effect). This peak turns out to be associated with the transition from the region of stable magnetization to superparamagnetism in contrast to other explanations of the Hopkinson effect. On the other hand, the magnetization increases monotonically when cooling the system from temperatures above T c. These results are compared with experimental data for barium hexaferrite powders.

Investigation of Interaction Effects in Barium Ferrite Powders by Remanence Curves

physica status solidi (a)Volume 137, Issue 1 p. K49-K52 Short Note Investigation of Interaction Effects in Barium Ferrite Powders by Remanence Curves H. Pfeiffer, H. Pfeiffer Institut für Physikalische Hochtechnologie, Jena Search for more papers by this authorW. Schüppel, W. Schüppel Institut für Physikalische Hochtechnologie, Jena Search for more papers by this author H. Pfeiffer, H. Pfeiffer Institut für Physikalische Hochtechnologie, Jena Search for more papers by this authorW. Schüppel, W. Schüppel Institut für Physikalische Hochtechnologie, Jena Search for more papers by this author First published: 16 May 1993 https://doi.org/10.1002/pssa.2211370138Citations: 1 Helmholtzweg 4, O-6900 Jena, Federal Republic of Germany. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume137, Issue116 May 1993Pages K49-K52 RelatedInformation

Synthesis of nano-sized barium ferrite particles using an inorganic dispersing phase

Nano-sized barium ferrite powders were successfully synthesized at temperatures below 600 °C without melting in a 0.313 BaO-0.258 B2O3-0.100, Na2O-0.330 Fe2O3 system, from an aqueous solution of corresponding salts. The change in crystallization behavior with varying decomposition conditions, and resultant magnetic properties were analyzed using x-ray diffraction, TEM, and vibrating-sample magnetometry, respectively. The defects which acted as nucleation sites for heterogeneous crystallization originated from decomposable constituents remaining up to the crystallization temperature. These defects were eliminated by spray drying and proper oxidation of the starting mixture before crystallization. Barium ferrite powders, having average particle size of 50–70 nm, showed a saturation magnetization (MS) of 38.37 emu/g, coercivity (HC) 2.9 kOe, and a squareness of 0.528.

On the Nature of the Demagnetized State and Interaction Effects in Barium Ferrite Powders

physica status solidi (a)Volume 136, Issue 2 p. K117-K119 Short Note On the Nature of the Demagnetized State and Interaction Effects in Barium Ferrite Powders H. Pfeiffer, H. Pfeiffer Institut für Physikalische Hochtechnologie, Jena Search for more papers by this authorW. Schüppel, W. Schüppel Institut für Physikalische Hochtechnologie, Jena Search for more papers by this author H. Pfeiffer, H. Pfeiffer Institut für Physikalische Hochtechnologie, Jena Search for more papers by this authorW. Schüppel, W. Schüppel Institut für Physikalische Hochtechnologie, Jena Search for more papers by this author First published: 16 April 1993 https://doi.org/10.1002/pssa.2211360240Citations: 1 Helmholtzweg 4, O-6900 Jena, Federal Republic of Germany. AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat Citing Literature Volume136, Issue216 April 1993Pages K117-K119 RelatedInformation

A Suggestion on the Standard X-Ray Powder Diffraction Pattern of Barium Ferrite

AbstractWe have examined the barium ferrite powder X-ray diffraction patterns in the PDF using experimental and calculated diffractograms. An improved calculated diffractogram is proposed. The result indicates that the primary peak of barium ferrite is not (107) but is (114).

Microwave absorption in single-domain particles involving first- and second-order uniaxial magnetic anisotropy constant

The ferromagnetic resonance absorption is calculated for powder assemblies of non-interacting magnetically uniaxial particles involving the anisotropy constants K 1 and K 2. It is shown that both constants can be obtained by FMR separately within a relative error of the second-order anisotropy constant rm|Δ K 2| = |0.01 K 1|. This determination method is applied on Co 2+/Ti 4+- and Zn 2+/Ti 4+-substituted barium ferrite with an amount of substitution of 0 ≤ x ≤ 1.25. For both substituted barium ferrite powders it is found that K 2 is less than the 1% of K 1. Consequently the decrease of the anisotropy field strength with substitution must be effected by the decrease of K 1 alone.