Ba Ferrite Research Articles

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.

Low-loss barium ferrite quasi-single-crystals for microwave application

Barium hexaferrites (BaFe12O19) are especially useful for microwave/millimeter devices. Due to large ferromagnetic resonance (FMR) loss (linewidths >2kOe), traditional compacts of polycrystalline Ba ferrites indeed hinder the utilization of the materials for practical devices. The present experiment demonstrates that the quasi-single-crystal Ba ferrite disks can be fabricated by a single solid-state reaction technique without liquid phase participation, combining with a processing of alignment for the ferrite seed crystals. The ferrite bulks show a pure hexagonal Ba ferrite phase, an expected 4πMs of 4.48kG, and coercivity of 10∼20Oe along the c axis, similar to the results of a typical single crystal. The FMR measurement indicates that the sample yields an anisotropy field of 16.0kOe and a linewidth of about 300Oe at U-band frequencies. Although the linewidth is broader than ideal Ba ferrite single crystals (ΔH<100Oe), it may be possible to reduce to 100Oe by eliminating pores, cracks, local grain boundary, and nonuniformity. In terms of material preparation, we believe that it is cost effective in the production of future microwave devices.

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

Influence of Co–Zr substitution on coercivity in Ba ferrites

Polycrystalline BaCo x Zr x Fe 11.5−2 x O 18.25 samples with 0 ⩽ x ⩽ 0.6 ions per formula units were prepared by modified citrate precursor method with the initial ratio of Ba:Fe equal to 1:11.5. The cationic site preferences of Co 2+ and Zr 4+ in Co–Zr substituted Ba ferrite were investigated by magnetic measurements and X-ray diffractometer (XRD) analysis. The coercivity H c was decreasing with increasing Co–Zr substitution. The datum showed that the max coercive force ( H c) was obtained when substitution of 0.2, while the best saturation magnetizations ( M s) was obtained when substitution of 0.4.

構造を形成する粒子分散系の流動挙動の研究

Rheological properties of particle suspensions, in which particulate coagulation structures are involved, have been described briefly. Magnetic Ba ferrite and/or smectite were selected as the dispersed particles. The flocs composed of both magnetic particle aggregation and immobilized medium components play an important role of suspension fluidity in such a manner that they make kinds of chains. High concentration of magnetic particles in the system results in the networks among these flocs or chains in a medium. In aqueous suspensions containing smectite particles which form "card house" structures by electrostatic interaction, different types of the networks among those clay particles exist in the dispersion system. Complicated rheological characteristics of the suspensions could be explained by the dynamical mode change in the networked coaguration structures.

Enhancement of GHz electromagnetic wave absorption characteristics in aligned M-type barium ferrite Ba1−La Zn Fe12−−(Me0.5Mn0.5) O19 (x=0.0–0.5; y=1.0–3.0, Me: Zr, Sn) by metal substitution

The resonance absorption properties depend on the complex permeability μ=μ′−jμ″, particularly μ″=Ms/2HAα and x of substitution amount for Ba and y of that one for Fe on the absorption properties of Ba ferrite compound. The c-axis aligned Zr-substituted samples (x=0.0, y=1.4) showed Ms=76 μWm/kg, HA=0.21 MA/m, and μ′=7.2 and μ″=7.0. These μ′ and μ″ are significantly larger than those for (TiMn)-substituted samples. Sn or Zr is concluded to be effective in enhancing the absorption characteristics of M-type Ba ferrite absorber.

C-axis oriented Ba–ferrite thin film with small grain for perpendicular magnetic recording

Hexagonal Ba–ferrite(BaM) thin films with amorphous AlO(a-AlO) under-layer were prepared by a facing targets sputtering system. The grain size of c-axis perpendicularly oriented BaM/a-AlO films is about 20 nm at the thickness of 20 nm for BaM layer. The perpendicular coercivity is about 3.5–4.3 kOe with BaM layer thickness in the range from 80 to 30 nm and 2.3 kOe for BaM layer thickness of 20 nm.The in-plane coercivity for BaM/a-AlO films was less than 0.1 kOe at the thickness ranging from 20 to 80 nm.

配向性Ｍ‐型バリウムフェライトＢａ１‐ｘＬａｘＺｎｘＦｅ１２‐ｘ‐ｙ（Ｍｅ０．５Ｍｎ０．５）ｙＯ１９における金属元素Ｌａ，Ｍｎ，Ｓｎ，Ｚｎ置換による高マイクロ波吸収特性への効果

Microwave radiation in the GHz band is increasingly being used in many various communication devices. However, this has brought about the problems of electromagnetic interference (EMI). Now M-type Ba ferrite is expected to be used as a powerful countermeasure to EMI. Our recent works have shown that M-type Ba ferrite is promising material for microwave absorber in the GHz range. The electromagnetic resonance absorption properties depend on the complex permeability μ=μ'-jμ", particularly the imaginary part μ"=Ms/2HAα(Ms: saturation magnetization, HA: anisotropy field, a: extinction coefficient). We investigated the effects of substitution composition (x) of Me for Ba (Me: La) and substitution composition (y) of Me ion (Me: Zn, Zr, Sn) for Fe3+ on the electromagnetic absorption properties of the Ba1-xLaxZnxFe12-x-y(Me0.5Mn0.5)yO19 compound. The c-axis aligned samples were formed into toroidal shapes. The magnetic properties (Ms, HA) and the resonance absorption properties (μr', μr" etc) were measured using a VSM and a network analyzer. The aligned Zr-substituted samples (x=0.0, y=1.4) showed values of HA =0.21 MAm-1, and μ'= 7.5 and μ" =7.1 that were higher than those of (TiMn) substituted samples. The matching thickness dm decreased to 0.8 mm at the matching frequency of 7.6 GHz. In the sample of x=0.0 and y=1.5, μ'=7.7 and μ" = 6.7 were obtained, and the matching thickness dm was 0.98 mm at 5.95 GHz. Also, Sn-substituted samples showed high m' and m" values of 6.3 and 6.3, respectively, and dm of 1.02mm. It is therefore concluded that Sn or Zr substitution is effective in enhancing the electromagnetic wave absorption characteristics of M-type Ba ferrite absorber.

Magnetic Study of Doped Ba Ferrites Prepared by Citrate Method

The M-type barium ferrite is doped with either Co2+-Ti4+ or Co2+-Zr4+ pairs to reduce its intrinsically high uniaxial magnetic anisotropy in order to make fine particles for magnetic recording. The magnetic parameters were investigated by magnetic measurements and the Mossbauer spectroscopy. Compounds (BaF) obtained from BaCo x (Ti,Zr) x Fe12-2xO19 with 0≤x≤1.0 have been prepared by the modified citrate method with the initial ratio of Ba:Fe equal to 1:10.8. The substitution of Co - Ti or Co - Zr for Fe3+ ions affects mainly the positions 2a and 4f2. Ba ferrite with the substitution x ≈ 0.8 is promising for perpendicular recording media applications.

Influence of Co–Ti substitution on coercivity in Ba ferrites

Polycrystalline BaCo x Ti x Fe 12−2 x O 19 samples with 0⩽ x⩽1.2 ions per formula units were prepared by modified citrate precursor method with the initial ratio of Ba:Fe equal to 1:10.8. The cationic site preferences of Co 2+ and Ti 4+ in Co–Ti substituted Ba ferrite were investigated by magnetic measurements and Mössbauer spectroscopy. The coercivity H c, specific magnetic polarisation J s-m( J s-r) and Curie temperature T c is decreasing with increasing Co–Ti substitution. The variation of these parameters can be explained by the replacement of the Fe 3+ ions in the 2b and 4f 2 sites, and by splitting the 12k site on the two magnetically non-equivalent sublattices (12k and 12k′), which reduces the effective uniaxial anisotropy of Ba ferrite.

Perpendicular magnetic recording media using hexagonal ferrite thin films deposited on Pt underlayers and interlayers

Ba ferrite (BaM) thin films with excellent c-axis orientation were deposited on Pt(1 1 1) underlayers using Facing Targets Sputtering system. BaM thin films with extremely low thickness, as thin as 8 nm, exhibited apparent c-axis orientation. Such thin BaM layers exhibited small grain size. BaM/Pt multilayered structure was also effective to introduce exchange interaction among BaM crystallites.

BaM/Pt multilayered films with fine grains and large perpendicular magnetic anisotropy for high density recording media

A magnetoplumbite type of Ba ferrite (BaM) thin layer was deposited on a 9 nm thick Pt underlayer, and excellent c-axis orientation was observed even for an 8 nm thick BaM layer, which corresponds to only three or four BaM unit cells. The grain size was almost in the same range of 60–85 nm even when the BaM layer thickness tBaM decreased from 60 to 17 nm, and tBaM should be reduced below 10 nm to make a grain size smaller than 50 nm. However, the perpendicular coercivity Hc⊥ and squareness S⊥ decreased drastically from 2.6 to 0.5 kOe and from 0.6 to 0.2, respectively, with the decrease of tBaM from 60 to 8 nm because of higher demagnetizing field and susceptibility to thermal fluctuation. On the other hand, the [BaM(5–24 nm)/Pt(9 nm)]3 multilayer exhibited higher Hc⊥ and larger S⊥ than the BaM/Pt bilayer for the same BaM layer thickness and Hc⊥ and S⊥ of the [BaM(8 nm)/Pt(9 nm)]3 multilayer was 2.0 kOe and 0.6, respectively. It was clarified that the deposition of the BaM/Pt multilayer was very effective for achieving a high perpendicular magnetic anisotropy constant even for the ultrathin BaM layer.

Improvement of read/write characteristics of sputtered Ba ferrite disks by adding Ta into Pt underlayers

Ba ferrite (BaM) disks with Pt and Pt-Ta underlayers were deposited by facing targets sputtering (FTS) apparatus. The effects of Ta addition into Pt underlayers on magnetic and crystallographic characteristics of BaM layers were investigated. The grain size of Pt-Ta underlayers was decreased with addition of Ta into Pt underlayers, and so the grain size of the BaM layers deposited on them decreased. The H/sub c/spl perp// and S/sub /spl perp// of Ba ferrite layers were increased with addition of Ta into Pt underlayers. Recording characteristics of BaM/Pt-Ta and BaM/Pt disks were investigated. BaM/Pt-Ta disks revealed better read/write characteristics than BaM/Pt disks due to their smaller grain size, high H/sub c/spl perp// of 3.4 kOe and larger S/sub /spl perp//. The D/sub 50/ value of 171 kFRPI was acquired in the BaM/Pt-Ta disk, which is promising for ultra-high density recording media.

磁性材料 磁気ディスク用Ｂａ及びＳｒフェライト薄膜の作製

Ba and Sr ferrite thin films with M-type magnetoplumbite hexagonal structure have the great advantage available to incorporate the magnetic disk recording layer without surface protective coating due to their highly chemical stability and wear durability. This paper reports the design criteria of thin film disk media, methods of film formation of Ba and Sr ferrite, heating techniques requiredfor crystallization, the investigation of grain size control.

Increase of coercivity and squareness ratio of by ferrite thin films by adding SiO/sub 2/ and substituting Al for Fe

Simple Ba ferrite (BaM) and SiO/sub 2/-added BaM (BaM:SiO/sub 2/) and Al substituted BaM (Al-BaM) films were deposited using the facing targets sputtering apparatus on SiO/sub x//Si wafers with Pt seed layers to enhance the c-axis orientation perpendicular to the film plane. Magnetic characteristics of the three kinds of BaM films were investigated and compared. Perpendicular coercivity H/sub c/spl perp// and squareness ratio S/sub /spl perp// of BaM:SiO/sub 2/ films increased to 4.2 kOe and 0.83, respectively, H/sub c/spl perp// and S/sub /spl perp// of Al-BaM films increased to 3.2 kOe and 0.89, but saturation magnetization M/sub s/ decreased to 2.9 kc. The magnetization reversal mechanism of BaM:SiO/sub 2/ and BaM films is not in coherent rotation mode but seems to be in the curling mode. The reason for high H/sub c/spl perp// of BaM:SiO/sub 2/ films is different from that of Al-BaM ones.

Adding SiO_2 to Increase Coercivity And Squareness Ratio of Ba Ferrite Films for Perpendicular Magnetic Recording Media

Adding SiO_2 to Increase Coercivity And Squareness Ratio of Ba Ferrite Films for Perpendicular Magnetic Recording Media

Fine barium hexaferrite powder prepared by the crystallisation of glass

In the present work, the glass strips (with dimensions 50 mm long, 6 mm wide and about 30–100 μm thickness) of the system Fe 2O 3–BaO–B 2O 3–Sb 2O 3 were subjected to heat treatments between 200°C and 780°C. The irreversible structure changes on the thermal annealings were studied by X-ray diffraction and by magnetic measurements. Crystallization of Ba ferrite at temperatures higher than 550°C was observed. The magnetic properties (specific magnetisation σ and coercivity H c) in terms of the evolution of size of BaFe 12O 19 crystals, dispersed in the glassy matrix were discussed. The particles produced by this method satisfy the stringent requirements better than the powders made by milling the polycrystalline materials manufactured by the usual ceramic way of preparation.

Enhancement of enzyme reaction of magnetically anisotropic polyacrylamide gel rods immobilized with ferromagnetic powder and ?-D-galactosidase in an alternating magnetic field

An immobilized polyacrylamide gel containing beta-D-galactosidase and Sr-Ba-ferrite was magnetized in a static magnetic field. The gel rods (10 mm long, O 2 mm) exhibiting magnetic anisotropy could move at lower than 100 Hz but not at higher than 250 Hz in an alternating magnetic field of 200 Oe. In case of immovability of gel rods, the apparent enzymic activity increased 3 times higher under exposure of an alternating magnetic field of 500 Oe (570 Hz). It could be explained that the ferromagnetic powder inside the gel might vibrate under the influence of elasticity of gel in the alternating magnetic field of 100 or 500 Oe and 0.2-12 kHz. This might facilitate faster diffusion of the substance inside the gel and transportation of the substrate and the product through the surface of gel. Consequently, the enzyme reaction was apparently activated.

Ａｌ置換ＢａＭフェライト薄膜の磁気特性

Al-substituted Ba ferrite (Al-BaM) films with a composition of BaAlxFe12-xO19 (Al content x = 0,1,2) were deposited on SiOx/Si wafers with Pt seed layers. A post-annealing process and high substrate temperature Ts are necessary to crystallize the films. With an increase of the Al content x in Al-BaM ferrite films, the saturation magnetization 4πMs decreased, while the perpendicular coercivity Hc⊥ increased, reaching over 3.3 kOe. The perpendicular squareness ratio S⊥ was increased to about 0.9 by substitution of Al for Fe. The Al-BaM ferrite films with suitable Hc⊥ and large S⊥ prepared in this study may be applicable as perpendicular magnetic recording layers with low noise levels.

A Ba Ferrite Disk Deposited at Low Temperature and Its Read/Write Characteristics

Magnetoplumbite-type Ba ferrite (BaM) layers were deposited on ZnO (002) and Pt (111) underlayers by using a facing-targets sputtering apparatus in a gas mixture of Ar, Xe, and O2 at various substrate temperatures Ts. A Ba ferrite layer as-deposited on a ZnO underlayer at Ts values above 475°C and one as-deposited on a Pt (mmm) under-layer at Ts values above 500°C revealed clear c-axis oientation. The saturation magnetization 4πMs was 5.1 kG and 4.0 kG for ZnO and Pt underlayers, respectively. Both underlayers exhibited high perpendicular coercivity Hc⊥ and low in-plane coercivity Hc// of about 2.4 and 0.2 kOe, respectively. A Ba ferrite layer deposited at a relatively low Ts of 300°C and annealed at 800°C in air also revealed excellent c-axis orientation and exhibited a relatively low perpendicular coercivity Hc⊥ of 0.6 kOe. A clear di-pulse was observed for the isolated wave form of a BaM/Pt film as-deposited at Ts of 600°C owing to the perfect perpendicular magnetization orientation, and a relatively high linear recording density D50 of 123 kFRPI was achieved.