Ba-ferrite Particles Research Articles

The temperature dependence of magnetic properties of Zn–Ti substituted Ba-ferrite particles for magnetic recording

It was shown that the morphological and magnetic properties of Zn–Ti doped Ba-ferrite particles are suitable for magnetic recording. In order to clarify the temperature dependence of the magnetic properties of these particles, BaFe 10.8−2 x Zn x Ti x O 19 particles with the nominal composition x=0.0–0.50 were prepared by synthesis from salt melts. The saturation magnetization M s, magnetic anisotropy field H A and magnetocrystalline anisotropy constant K 1 of the above-mentioned particle assemblies were estimated by using the law of approach to saturation of polycrystalline ferrite, and the Curie temperature T c was determined by the thermodynamic relation. With an increasing x, the T c decreased, while the lattice parameters a, c and M s have an unnoticeable maximum at x=0.20. The H c( T) curves of samples with different x show that all particles have positive temperature coefficient in the vicinity of room temperature, which decreases with increasing x. The M s( T), H A(T) and K 1(T) were determined and discussed.

Magnetic Properties of Co–Sn Substituted Barium-Ferrite Particles for Magnetic Recording

In order to improve the margin for operating temperature changes and to achieve high recording performance, Co–Sn substituted Ba-ferrite particles were investigated. It was found that BaFe12—2xCoxSnxO19 particles with x = 1.10 to 1.40 not only have a coercivity suitable for magnetic recording, but also have a very low temperature coefficient of coercivity ΔHc/ΔT in the temperature range from 0 to 60 °C.

Magnetic Properties of Co–Sn Substituted Barium-Ferrite Particles for Magnetic Recording

In order to improve the margin for operating temperature changes and to achieve high recording performance, Co-Sn substituted Ba-ferrite particles were investigated. It was found that BaFe12-xCoxSnxO19 particles with x = 1.10 to 1.40 not only have a coercivity suitable for magnetic recording, but also have a very low temperature coefficient of coercivity Delta H-c/Delta T in the temperature range from 0 to 60 degrees C.

Structure and magnetic properties of Zn–Ti-substituted Ba-ferrite particles for magnetic recording

The formation process of Zn–Ti-doped Ba-ferrite particles was investigated by the X-ray diffraction technique, transmission electron microscope and magnetic measurements. The effects of heating temperature T h and the Zn–Ti substitution x on the microstructure and magnetic properties of BaFe 12−2 x Zn x Ti x O 19 particles with x=0.10–0.80 were studied. The temperature dependence of magnetic properties of these particles was measured.

The Effects of Hydrogen Reduction on Magnetic Properties of Barium Ferrite Particles

A reduction process of the substituted Ba-ferrite has been found to be devided into three steps. At the first and second steps, the magneto-plumbite structure maintains and the coercivity increases. When the reduced-substituted Ba-ferrite particles are reoxidized, the coercivity is reversible in the first step but irreversible in the second step. During the third step, the magneto-plumbite structure was collapsed with formation of α-Fe and BafeO 3-x phases and consequently the coercivity distribution was broad and the coercivity irreversible. The coercivity and saturation magnetization decreases and increases up to 130 emu/g respectively. In this study, it is found that the substituted cations prevent the magneto-plumbite structure from collapse during the reduction process and furthermore migrate from the magnetic sites of 4f N +2a, 2b. and 12k to 4f VI and 12k'. An increase in the coercivity before the collapse of magneto-plumbite structure is attributed to the migration of substituted cations in hexagonal Ba-ferrite structure.

Magnetic Properties and Crystal Structure of Composite Ba-ferrite Particles Containing α-Fe

Composite Ba-ferrite particles containing α-Fe were prepared by reducing Co–Ti–Sn substituted Ba-ferrite platelet particles in a hydrogen gas atmosphere. The coercivity of the composite particles increased to about three times that of the starting Ba-ferrite, and a magnetic easy cone appeared when the saturation magnetization grew larger than 62 emu/g. The substitution cations, particularly the Ti ions, were shown to inhibit the transformation of the crystal structure through reduction. The enhanced coercivity observed in the composite particles was due to the decrease of both Co ions as the substitution element and iron ions at the 12k site. The magnetic easy cone seemed to be caused by the formation of paramagnetic iron ions in the particles, which interrupted the superexchange interaction between magnetic iron ions.

Magnetic Anisotropy of Ba Ferrite Particles at Low Temperature

The evolution of the magnetic anisotropy of pure and Co/Ti-doped Ba ferrite particles from room to low temperatures is studied analyzing the variation of the anisotropy constants with T. These constants increase with the decrease of temperature in different ways in the two types of particles. In pure particles the magnetocrystalline anisotropy constant K 1 is larger than the conflicting shape anisotropy constant K s at low as at room temperature, which means uniaxial anisotropy, in all the analysed range of temperatures. In the doped particles, where the substitutions weaken the crystalline anisotropy, at low temperature K s > K 1 , then the particle is not any more uniaxial, but the easy have multiple directions.

The Temperature Dependence of Magnetic Properties of Zn-Ti Substituted Ba-ferrite Particles for Magnetic Recording

It was shown that the morphological and magnetic properties of Zn-Ti doped Ba-ferrite particles are suitable for magnetic recording. In order to clarify the temperature dependence of magnetic properties of these particles, BaFe10.8−2XZnX TiXO19 particles with the nominal composition X= 0.0-0.50 were prepared by synthesis from salt melts. The saturation magnetization Ms, magnetic anisotropy field HA and magnetocrystalline anisotropy constant K1 of above-mentioned particle assembly were estimated by using the law of approach to saturation of polycrystalline ferrite and the Curie temperature Tc was determined by the thermodynamic relation. With an increasing X, the Tc decreased, while the lattice parameter a, c and Ms have an unnoticeable maximum at X=0.20. The Hc(T) curves of samples with different X show that all particles have positive temperature coefficient in the vicinity of room temperature, which decreases with increasing X. The Ms(T), HA(T) and K1(T) were determined and discussed.

Neutron depolarisation and noise studies of Ba-ferrite tapes as a function of milling time

Ba-ferrite particles have been dispersed and coated onto polyethylene terephthalate (PET) film and magnetic structure investigated using a range of magnetic measurements including noise studies and neutron depolarisation (ND). Noise measurements were made on lengths of tape for samples cycled through Isothermal Remanent Magnetisation (IRM) and DC Demagnetisation (DCD) measurement processes and interpreted in terms of the total noise power and spectral response. ND measurements were analysed in terms of magnetic correlations within the films. Total noise power exhibited a minimum around the remanent coercivity (H/sub r/), as observed for most particulate media. ND values of correlation function, /spl zeta/ displayed a peak rather than a dip around H/sub r/. The similarity in the respective peak/dip positions indicates that both measurement techniques were sensitive to the same micro-structural details.

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.

Effects of dispersion on interaction and orientation in barium ferrite tapes

Interactions between Ba-ferrite particles have been examined from measurements of remanence curves. Hand-spread tapes with different degrees of orientation, controlled by the orientation field and milling time, have been studied. The results show that the effect of the orientation field is to improve the easy axis distribution. Thus, as milling proceeds, squareness, the peak value of the Δ/( H) curve and the degree of easy axis orientation, all increase. Towards the end of the milling process, the tendency to stack is reduced as the dispersion quality improves and this reduces the orientational texture.

Time-dependent magnetic behaviour of Ba ferrite particles at low temperature

The time dependence of the magnetization of pure and Co/Ti-doped Ba ferrite particles is analysed at low temperatures and compared with the dependence at room temperature. In undoped particles the variation of the magnetization and the magnetic viscosity are smaller at low than at room temperature, as expected from the increase of thermal stability of the magnetization with the decrease of temperature. On the contrary, in Co/Ti-doped particles for magnetic recording media, we observe an anomalous increase of the magnetization variation during the time and of magnetic viscosity when the temperature decreases. This behaviour is interpreted on the basis of the evolution of magnetic anisotropy with the temperature in doped Ba ferrite particles, where the magnetocrystalline anisotropy at low temperature becomes comparable with the shape anisotropy.

定圧濾過法によるバリウムフエライト微粒子を含む磁性塗料の粒子分散状態評価

六角板状のバリウムフェライト微粒子を含む磁性塗料について, 塗料中における粒子分散状態を直接評価することを目的として定圧濾過測定を行った。塗料作製時の分散処理時間が異なる塗料について測定した結果, 一定時間濾過後の塗料総流出量は, 分散時間の増加に伴い増加する傾向を示し, 粒子分散状態が改善されていることが確認された。さらに, 得られた濾過データを定量化するためこの系における濾過機構を検討したところ, 標準閉塞型と一致することが判明した。標準閉塞型を表す理論式からそれぞれの塗料について閉塞定数および最大濾液流出量が算出され, これらのパラメーターは他の測定法から得られる塗料および塗膜物性と良好な相関を示し, 塗料内粒子分散状態の指標として有用であることが確認された。

Remanence properties of substituted Ba-ferrite particles for high density magnetic recording

In this paper, the remanence properties of Co-Sn, Co-Ti and Co-Ti-Sn substituted Ba-ferrite (BaF) oriented particulate samples are compared with those of some oriented acicular particulate samples. A new parameter, the minor remanence distribution (MRD), is proposed to review the remanence properties of magnetic particles and the capabilities for resisting the recording demagnetization of magnetic recording media. It is shown that the MRD values of the oriented BaF particulate samples were smaller compared to oriented Co-/spl gamma/-Fe/sub 2/O/sub 3/ samples, even though the squareness ratios (SR) of some of the BaF samples were smaller than those of the Co-/spl gamma/-Fe/sub 2/O/sub 3/ samples. It Is the small MRD, SFD/sub r/, IRS and large DH/sub r/ of a medium that can result in a large resistance to the effects of recording demagnetization and therefore in superior characteristics for high density magnetic recording. Since Co-Sn substituted BaF platelet-shaped particles exhibit these characteristics and have a very low temperature coefficient of coercivity, these particles can be expected to be a promising candidate for high density magnetic recording. >

Micromagnetic calculations in Ba-ferrite small particles configuration energy during the magnetisation reversal

Abstract We have made numerical simulations of Ba-ferrite single particles of different sizes but with the same prismatic shape. We have found the magnetisation reversal mechanism as well as the configuration energy during this process to depend strongly on the size of the particle. This dependence has the form KVφ ( V ) where φ ( V ) is a decreasing function of the particle volume V .

Development and Preparation Processes of Barium Ferrite Particles for Magnetic Information Storage.

The preparation processes, morphlogical, structural and magnetic properties of BaFe12-2X (CoTi) XO19 and BaFe12-2X (CoSn) XO19 fine particles, prepared by chemical coprecipitation, synthesis from salt melts and glass crystallization method were investigated. The correlation between the magnetic properties, the particle morphology and the degrees of Co Ti and Co Sn substitutions of Ba ferrite particles were studied. These substituted Ba ferrite particulate media are of great interest for high density magnetic information storage.

Characteristics of thin layer particulate recording media

Thin layer particulate recording media with a nonmagnetic under layer have been developed with double coating techniques, and their high performance have been confirmed. Such media produce a higher output than single and thick layer media because they have a smooth surface resulting from the under layer smoothness and less demagnetization resulting from the thinness of the magnetic layer. The application of Ba-ferrite particles to thin layer media, in addition to metal particles, has clarified the differences between the characteristics of the two media. The output of thin layer metal media has been improved by up to +9dB compared with the value for reference metal media. Thin layer Ba-ferrite media showed lower noise.

Developments and advances in thin layer particulate recording media

Thin layer particulate recording media with a nonmagnetic under layer have been developed with double coating techniques, and their high density characteristics have been confirmed to be excellent. Such media produce a higher output than single and thick layer media because they have a smooth surface resulting from the under layer smoothness and less demagnetization resulting from the thinness of the magnetic layer. Such media produce a sharp and symmetrical isolated pulse waveform and show good overwrite characteristics for digital recording. The application of Ba-ferrite particles to thin layer media, in addition to metal particles, has clarified the differences between the characteristics of the two media. The output of thin layer metal media has been improved by up to +9 dB compared with the value for reference metal media, largely by improving the metal particles. Thin layer Ba-ferrite media are characterized by high output and low noise in the short wavelength region. Such performance will be expected for any particle orientation.

Cation site preference and magnetic properties of Co-Sn-substituted Ba ferrite particles

The magnetic properties and the cation site preferences of Co 2+ and Sn 4+ in Co-Sn-substituted barium ferrite (BaF) were investigated by magnetic measurements and Mössbauer spectroscopy. It was shown that Co 2+ and Sn 4+ cations prefer to occupy 4 f VI , 2b and 12k crystallographic sites. The dramatic decrease in coercivity H c of the substituted BaF particles, with increasing substitution χ from 0.2 to 1.4, could be explained by the Co 2+ and Sn 4+ preferences for 4f VI and 2b sites, which weakened the effective uniaxial anisotropy of BaF. The decrease in the Fe 3+ at 12k lattice sites was the major reason for the linear reduction in the specific saturation magnetization σ s with increasing χ. The conditions of the above Co-Sn-substituted BaF were different from those of Co-Ti-substituted BaF.

Two-variables scaling of the magnetic viscosity in Ba-ferrite nano-particles

Careful measurements of the magnetic viscosity S = d M/ d ln t of non-oriented nano-particles of Ba-ferrite (317 Å as mean diameter) show a remarkable scaling plot vs. two variables: the usual T ln( t/τ 0 and the applied magnetic field H. This plot takes into account two distributions, the particle size ρ( s) and the switching field v( H 0) distributions. This last plays a dominant role on the magnetic viscosity of Ba-ferrite particles at low temperature. Taking a Lorentzian distribution for v( H 0), one derives from the measured magnetic viscosity a particles size distribution ρ( s) which is exactly the same as the distribution observed directly by transmission electron microscopy. The agreement, obtained without free fitting parameter, allows to reproduce all typical features of the S( H, T) showing that ρ( s) and v( H 0) are the relevant distributions. This approach allows to avoid erroneous interpretations of S( H, T) at low temperatures. In particular bimodal distributions, sometimes derived from magnetic viscosity experiments might, in some cases, be attributed to a convolution of ρ( s) and v( H 0).