Ba-ferrite Particles Research Articles

Morphological, Structural and Magnetic Properties of Zn-Ti Substituted Ba-Ferrite Particles For Magnetic recording

Morphological, Structural and Magnetic Properties of Zn-Ti Substituted Ba-Ferrite Particles For Magnetic recording

Preparation and properties of La-doped barium ferrite/poly (3-methylthiophene) composites

La-doped barium ferrite/poly(3-methylthiophene)(LB/P3MTH) composites have been successfully synthesized by in suit chemical polymerization with ferrite chloride (FeCl3) as an initiator. The composites structure is investigated by X-ray diffraction analysis (XRD) and Fourier transform infrared spectroscopy, and the morphology of samples is observed by transmission electron microscopy (TEM). Magnetic properties of the composites are tested by vibrating sample magnetometer. XRD analysis shows that La3+ has got into the lattice of Ba-ferrite and replaces the Ba2+ and that the best La3+ amount of La-doped Ba-ferrite is not more than 0.08. La-doped Ba-ferrite particles are coated with poly (3-methylthiophene). TEM image reveals that La-doped Ba-ferrite particles have spherical morphology and are agglomerated due to the coated polymer. P3MTH covers the ferrite surface and has crystallite boundaries, which influences the composites’ physical and chemical properties.

Percolation Conduction in Hybrid Thermoelectric Material Consisting of Bi0.88Sb0.12 and Barium Ferrite Particles

A hybrid material consisting of thermoelectric Bi0.88Sb0.12 and Ba ferrite Bi0.88Sb0.12(BaFe12O19)x (x = 0, 0.025, 0.04, and 0.08) was synthesized using sintering. Powder x-ray diffraction patterns and scanning electron microscopy images of the hybrid indicate that the BaFe12O19 particles were well distributed in the host Bi0.88Sb0.12 phase. The temperature dependence of the electrical resistivity ρ of the host Bi-Sb exhibits metallic behavior. By the addition of Ba ferrite particles, the ρ at 300 K increases intensively, and ρ(Τ) then behaves similarly to a semiconductor. However, it is noted that the thermoelectric power S is unchanged. Inhibition of current and heat flows by a restricted conduction path and the unchanged electromotive force generated by the Seebeck effect in the conduction path can be understood based on a site-percolation model consisting of conducting Bi-Sb and insulating Ba ferrite. The critical volume fraction pc of this system was estimated experimentally as pc = 0.68.

Investigation on the magnetic anisotropy of particulate and thin film recording media

Some aspects of the magnetic anisotropy of fine particles and thin films, employed in longitudinal recording media, are studied. The analysis is carried out through the measurement of perpendicular magnetization and the calculation of the second derivative, which allows to obtain the distribution of anisotropy fields. In assemblies of α-Fe metal particles, where shape anisotropy prevails, the evolution of the anisotropy field distribution with packing is studied. In Ba ferrite particles, where both magnetocrystalline and shape anisotropy are present and comparable, the effect of the ionic substitutions is analyzed. In thin film media, a comparison between magnetic layers with different composition (ternary and quaternary Co-based alloy) is carried out. In all materials, the relevance of the analysis of the whole distribution is underlined. From the anisotropy results, information on the magnetization switching is drawn.

Experimental studies of fluctuation field and temperature coefficient of coercivity in advanced data backup tapes

The reverse field dependence of the normalized magnetization decay and the fluctuation field (Hf)was examined for advanced data backup tapes prepared from ultrafine acicular metal particulate (MP) composite and hexagonal platelet Ba-ferrite (BF) particles. Also, the effect of the ratio of Hf to coercivity (Hc) on the temperature coefficient of coercivity [α(Hc)] was studied at 300 K. In comparison to MP and BF tapes with approximately the same mean volume of particles (Vphy), the normalized magnetization decay of BF tapes was much larger than that of MP tapes. The smaller the Vphy was, the larger the normalized magnetization decay became. The values of Hf were not constant, but were largely dependent on the reverse field. In the low reverse fields, Vphy was smaller than the activation volume for both tapes with very small Vphy. The value of α(Hc), which is very important for the thermal stability of high-density recording media, increased as the ratio Hf∕Hc increased for both tapes.

Magnetic Alignments of Ba-Ferrite Particles in Suspension

Ba-ferrite particles were dispersed into distilled water to make stable slurry, which was then slip cast in transverse magnetic field. The water drainage from the slurry was performed by vacuum evacuation to solidify the slurry into a cake – like sample. To obtain high degree of alignments, the slurries were slip cast in static – / pulsed – magnetic field and by using two separate steps of magnetic orientation and drainage. The particles turned their faces to the magnetic field and formed long chains stacked immediately while the magnetic field was applied, of which high induction density led to high degree of alignments. It is necessary to correspond with the drainage, gravity and magnetism so as to suppress the tendency of distortion or cracking of the sample as the aligned long chains of the particles tend to break into pieces and cave in randomly, which eventually destroys the particle alignments.

Evolution With Temperature of the Magnetic Anisotropy of Ba Ferrite Particles

The magnetic anisotropy of pure and Co/Ti-doped Ba ferrite particles is analyzed through the evaluation of the dependence on temperature of the constants of magnetocrystalline and shape anisotropy, which both are present in the platelet-like Ba ferrite particles with hexagonal structure. In undoped Ba ferrite, the magnetocrystalline anisotropy constant is predominant on the conflicting shape anisotropy constant at all temperatures, which indicates that the magnetic anisotropy is uniaxial, with preferred direction for the magnetization along the c axis of the hexagonal particles. In doped particles, where the magnetocrystalline anisotropy is weakened by the ionic substitutions, while at high temperatures the magnetic anisotropy is substantially uniaxial with c as axis of easy magnetization, when the temperature decreases, the shape anisotropy constant becomes larger than the magnetocrystalline anisotropy constant, and consequently, the magnetic anisotropy is not uniaxial, but it presents multiple preferred directions for the magnetization

Nanocrystalline iron oxide and Ba ferrite particles in the superparamagnetism–ferromagnetismtransition range with ferrofluid applications

Magnetic fluids based on Ba hexaferrite as well as iron oxide particles with enhancedanisotropy barriers show heating effects in ac magnetic fields which may be usefulin technical processes as well as medical applications (magnetic hyperthermia).Such particles also allow the detection of biological binding reactions through anenhanced Néel relaxation time above the Brown relaxation. The loss processesand the relaxation times depend strongly on the mean particle size and the sizedistribution width. To influence and improve the mean size as well as the sizedistribution, new approaches to the preparation are promising, where nucleation andgrowth of the particles can be influenced independently or where further growth ispossible on small given particles without further nucleation. We used a glasscrystallization method for preparation of nanocrystalline Ba hexaferrite as well asmagnetic iron oxide and a cyclic growth method based on ‘conventional’ precipitationfor iron oxide preparation. Properties of the powders prepared, as well as waterbased ferrofluids, were analysed using x-ray diffraction, transmission electronmicroscopy and magnetic methods. Values of the specific loss power of the order of100 W/g maghemite may be achieved with the option of further increase by improving the core size distribution.

Correlation of thermal stability and anisotropy distribution in data storage tapes prepared from ultrafine particles

The correlation between thermal stability and anisotropy field (H/sub A/) distribution was studied for data storage tapes prepared from ultrafine metal particulate (MP) composition and Ba-ferrite particles. At low temperature, the thermal effect had no influence in either tape. H/sub A/ distributions in easy direction of both tapes were excellent at 77 K. The angular distribution of H/sub A/was sharp in the case of MP tape, whereas the easy axes were widely distributed in the case of Ba-ferrite tape. In the easy direction, a proportion of particles had low anisotropy values in both tapes at 350 K. The normalized magnetization decay of MP and Ba-ferrite tapes in a -0.5 kOe field at 350 K was 0.4 and 1.4%/decade, respectively, and the respective thermal stability factors were 81 and 49. The magnetization stability is essentially determined by the magnitude and angular distribution of H/sub A/.

Microstructure and Hysteresis Model Parameters of Hard Magnetic Ferrites

The hysteresis in anisotropic Sr ferrite grains and Ba ferrite particles is described by statistical magnetization reversal behavior using phenomenological parameters. Consequently, these parameters are related to spontaneous magnetization, anisotropy, and microstructure geometry, using dimensionless microscopic constants.

Magnetization reversal in Ba-ferrite glass ceramics observed by neutron depolarization techniques

The mean domain size and the preferred orientation of the domain magnetization were observed in Ba-ferrite glass ceramics containing 22 vol% BaFe 12O 19 during magnetization reversal along the remanent and the demagnetizing branch. Except for the virgin state, the mean domain size, as measured by the magnetic correlation length, exceeds the mean particle size considerably. The maximum during the magnetization reversal attains 1 μm in comparison to 240 nm in the virgin state. This fact and the preferred orientation of the domain magnetization indicates that strong correlations are introduced between the Ba-ferrite particles during the magnetization process.

Magnetic properties of Me–Zr substituted Ba–hexaferrite

Substituted M-type Ba hexaferrites of composition BaFe 12−2 x Me x Zr x O 19 were investigated, where Me stands for Ni 2+, Co 2+ or Zn 2+. The series with x varying from 0 to 0.6, were prepared by two processing routes. A Fe/Ba ratio of 10 for mechanical alloying and of 10.8 for the citrate precursor method was chosen. It was shown that (Co, Ni, Zn)-Zr doped Ba ferrite particles have positive temperature coefficient of H c, which decreases with increasing x.

Ba-ferrite particles for magnetic liquids with enhanced Néel relaxation time and loss investigations

Ba-ferrite particles for magnetic liquids with enhanced Néel relaxation time and loss investigations

Characteristic correlations between the Δm* interaction curves and the Preisach diagram in particulate media

Magnetic interparticle interactions are analyzed by Δm* curves calculated from the initial magnetization curve and the hysteresis loop, instead of the usual deviation Δm based on remanence curves. This study is made on tapes of acicular CrO2 particles and on tapes of CoTi-doped Ba ferrite platelet-shaped particles. The standard Preisach map of the samples is experimentally constructed and the Δm* values, computed from this map, and the values agree fairly well with the Δm* curves measured for the ac demagnetized state and various dc demagnetized states. We describe a procedure for remagnetizing the dc demagnetized samples. For the acicular particles, the peak of the remagnetized curves is lower than that computed from the Preisach map. The opposite occurs for the platelet-shaped particles. This different behavior is ascribed to the different influence of the statistical interaction field and the mean interaction field.

Ｂａフェライト媒体のＤｅｌｔａ‐Ｍ測定と磁化の熱的安定性

Activation volume and inter-particle in interaction were evaluated using superfine Ba-ferrite-particle-coated media, which were either oriented or non-oriented. It was clarified the peak value of the ΔM plot, which was used for evaluation of inter-particle interaction, changes according to the degree of media orientation. The activation volumes of superfine particulate media were found to be twice as large as their physical volumes. This suggested that more than two particles are stacked and act together in magnetization reversal. The effective value of KuVac/kT was also estimated. For media composed of superfine Ba ferrite particles with diameters of about 22 nm, the KuVac/kT values were close to the critical value in thermal stability.

Inter-particle interaction and thermal stability of ultra-fine Ba ferrite particles for high-density recording

Newly developed ultra-fine Ba ferrite particles, having the mean diameters of 21.9–41.5 nm, were used to prepare encapsulated powder samples and sheet samples. The powder samples and non-oriented sheet samples exhibited almost zero amplitude in Δ M peaks; however, the longitudinally oriented sheet samples showed positive Δ M peaks, implying that positive interaction acts among particles. It was clarified that this positive interaction accelerates magnetization time decay, when the applied reverse field is greater than some fraction of H c, but it suppresses the time decay when the reverse field is smaller than the value. The magnetization time decay in the presence of a large reverse field was noticeable when particle diameters were <30 nm.

(Zn, Ni, Ti) substituted barium ferrite particles with improved temperature coefficient of coercivity

The Ba-ferrite particles have a positive temperature coefficient of d H c/d T. From the viewpoint of recording system applications, the d H c/d T should be reduced in order to improve the operating margin for temperature change. It was shown that the coercivity, H c, of Ba-ferrite particles is mainly controlled by the crystalline anisotropy. In the Ba-ferrite there are five distinct crystallographic sites or sublattices, and the Fe 3+ ion located on different site has different contribution to crystalline anisotropy. The replacement of Fe 3+ ions by Zn 2+, Ni 2+, and Ti 4+ ion will effect on the saturation magnetization σ s, coercivity H c and their temperature coefficients. The Zn–Ti, Ni–Ti, and Ni–Zn–Ti substituted Ba-ferrite particles were investigated. It was found that the Zn–Ti substituted Ba-ferrite particles have higher σ s, but large temperature coefficient of coercivity d H c/d T. In the case of Ni–Ti and Ni–Zn–Ti substitution the d H c/d T could be reduced to a small value, near to zero or negative value, while the σ s decreases very slowly with increasing the amount of substitution.

Magnetic interactions and media noise in rigid disks

This paper discusses the relationship between media-noise and magnetic properties. Two topics in longitudinal barium ferrite (Ba-ferrite) particulate rigid disks are mainly investigated; the relationship between media-noise characteristics and interparticle magnetic interactions, and the particle-size effect in read/write properties. For the first topic, a series of longitudinal Ba-ferrite disks with a variation in volumetric particle-packing densities are investigated. The magnetomotive force dependences or reverse DC-erase noise are measured and compared with interaction field factor. For the second topic, the particle-size effect in read/write properties of Ba-ferrite particulate disks are described compared with the those of Co–γFe 2O 3 particulate disks. The magnetic interactions in Ba-ferrite disks consist of two mechanisms: the interparticle positive interactions in stacks of Ba-ferrite particles, and the negative interactions between the stacks in which the magnetic moments of the Ba-ferrite platelet particles are aligned in the stack direction. H c and switching field distribution values depend on interparticle interactions and extra stack-like particle interactions. Media noise depends on particle size. These ideas are effective for thin film media without exchange of magnetic interactions.

Preparation and properties of barium-ferrite-containing glass ceramics

Magnetic properties of magnetic ceramics are dependent on the magnetisation processes. They are usually dominated by Bloch-wall displacements in multi-domain structures of the sintered magnetic material, even if the starting powder material shows single-domain Stoner–Wohlfarth behaviour. Domain wall motion limits in several cases the quality of magnetic materials for special applications like permanent magnets or rf devices. We have developed a new type of magnetic powder preparation which permits the fabrication of compact glass ceramics containing Ba-ferrite maintaining the single-domain behaviour of the starting powder. This technology is based on the glass crystallisation method for the precipitation of single-domain Ba-ferrite particles in a quenched melt of Fe 2O 3–BaO–B 2O 3(-SiO 2). By milling the crystallized melt or leaching out the borate from the SiO 2-containing glass, a glass ceramic powder containing Ba-ferrite can be produced, which can be sintered at moderate temperatures providing a dense compact glass ceramic containing up to 90 wt% Ba-ferrite. This compact glass ceramic shows the same single-domain behaviour as the starting powders, i.e. it also possesses the high coercivities of hard magnetic material.

Magnetic anisotropy distribution in Ba ferrite particles

The distribution of anisotropy fields in Ba ferrite particles and its evolution with the addition of Co/Ti ions is studied. The width of the anisotropy distribution increases with increase in doping content, and further is larger at low temperature. The result is ascribed to the role of the shape anisotropy, the effect of which is enhanced by doping and decreasing temperature.