Present paper discusses in detail the present status of the Industry and growth in the production of ferrites in India during last ten years. Ferrite production has shown better growth rates than many of the electronic components. There are many intrinsic advantages of producing this material in India like, easy availability of raw materials, skilled manpower, and research back-up etc. Such factors are discussed in the light of likelihood of India becoming a significant player in the global market. Production estimates till the year 2000 AD are also discussed.
Ferrite industry in Korea has been grown rapidly with the expansion of domestic electronics and steel industries. There has been much progress in both the production and the processing technology, but presently ferrite industry is confronted by the difficulties to be coped with. This paper focuses on the past, present and future of the ferrite industry in Korea including the demand and supply of iron oxide as raw materials, soft and hard ferrites.
This paper focuses on recent developments in the field of soft ferrites in Japan especially in consideration of environmental problems. With the rapid development of the electronics market, the ferrite industry has grown to a considerable size. Main raw material of ferrites, ferric oxide, has been supplied by steel mills from waste acid recycling systems. Recent deveropment of collecting and recycling system for used dry batteries in Japan, can be utilized for the raw materials of MnO and ZnO for Mn-Zn and MnMgZn ferrites. Another technical attempt is to lower the amount of poisonous additive from ferrite devices. Development of stress-insensitive PbO free NiCuZn ferrite is discussed.
It is shown that the Holstein Hamiltonian for a small polaron in the correlated motion approximation accounts for the linear dependence of resistivity on temperature in high Tc oxide superconductors. It also explains giant magnetoresistance in manganites when the activation energy is considered to depend on the long-and short-range atomic and magnetic order parameters.
The crystal structure of the low-temperature phase V of the distorted-triangular-lattice antiferromagnet RbMnBr3 is thought to be a zigzag-row model with the space group symmetry Pbca (Z = 8) which is deduced from the extinctions of the possible reflections in the diffraction experiments. The spin-ordered states of RbMnBr3 under magnetic fields in the ab plane are suggested to be qualitatively explained by the row model studied by Zhitomirsky.
Magnetic ceramics belonging to lithiun ferrite and magnesium ferrite inherently possess rectangular hysteresis loop and have found extensive use in microwave components. Molecular engineering of the ferrite composition and employment of appropriate process parameters are exploited to tailor the material properties for specific needs. Substitution of various tetravalent metal ions in combination with divalent magnesium have been attempted in lithium ferrite. Inclusion of germanium and titanium up to 0.5 ions/FU and tin up to 0.2 ions/FU yielded single phase spinels while with silicon a ferrite-glass composite was formed. Compositions with zirconium resulted in multiphase materials. The different magnetic properties of technical importance for their utility in components have been investigated and the observed behaviour is discussed on the basis of site occupation of the metal ions in the crystal structure and accompanying microstructural developments.
Lithium and magnesium ferrites find extensive use in microwave applications. Mixed LiMg ferrites have also been widely investigated. This paper presents findings of the studies carried out on two series of LiMg and LiMgTi ferrites with Zn substitution. The dc conductivity and thermopower measurements were carried out over wide temperature range. The main feature observed is opposite behaviour of Seebeck co-efficient variation with temperature in the two series which indicates the existence of two distinct charge transport mechanisms-hopping and band conduction. The critical temperature values obtained from magnetisation, conductivity and thermopower measurements agree very well with one another.
The variation of dielectric constant (∈) for Zr/Ti substituted Mn-Zn ferrites have been studied as a function of dopant concentration, frequency and temperature. The dielectric loss (tan δ) is also studied for all the materials varying the dopant concentration as well as frequency. Results are interpreted based on the existing theoretical models. The maximum tan δ is found to be occur at 10KHz for Ti doped ferrites, unlike Zr doped ferrites exhibit this type of behaviour.
By substituting Zr/Ti in the matrix of Mn-Zn ferrites, Tc, Ms, μi, K, Hc and Ph parameters are studied. The variations are explained on the basis of cation preferential sites and hence with the modified strength of exchange interactions of cations. Due to non-magnetic behaviour of the dopants, magnetic properties are decreased and the Hc values are increased. The hysteresis loss (Ph) values are decreased with the substituent concentration increasing the quality of the material.
Mixed ferrospinel with a general formula LixMxMg(1−2x)Fe2O4(for M=Cr,Mn,Fe,Co for x=0,.25 and 5) are prepared by ceramic technique. Formation is checked by XRD and all compounds are cubic spinels even in presence of J-Tions with lattice dimensions ranging from 8.30 to 8.37A. Charge and site distribution is obtained from diffraction data supported by electrical and magnetic parameters. The compounds are semiconducting with energy of activation ranging from 0.25 to 0.63ev. The observed magnetic results(Guoy and n-d) are explained by Neel's model or by Yafet-Kittel model.
Two series of Mn-Zn ferrites are prepared by the substitution of Sb5+ and Mo6+ separately. The variation of Tc, Ms, Hc, Br/Bs and Dg parameters with the dopant concentrations have been studied. Tc and Ms are found to decrease with dopant concentration except at 0.1 concentration of antimony. The grain size value is found to increase for Mo doped ferrites and decrease for Sb doped ferrites. The area of hysteresis loops for all the specimens is found to be decrease increasing quality factor.
The magnetic viscosity coefficient (Sv), the activation volume (Vact), the rotational hysteresis integral (Rh) and the average anisotropy field (HA,ave) were examined for acicular BaCoxTixFe12-2xO19 (x=0-1.0) particles prepared by a conventional sintering method. Acicular hexagonal Ba-ferrite particles with different coercive force (Hcj=35-310 MA/m) were prepared, and the dependence of Vact, Rh and HA,ave on Hcj was investigated. The results show that Hcj is proportional to Vact−2.2, as in the case of the platelet Ba-ferrite particles, SrM particles, SrW and Sm2Fe17Nx magnets, which all have a similar mechanism of magnetization reversal. Also, HA,ave increases with increasing Hcj and Vact is inversely proportion to the average anisotropy constant. It was found that Rh and Vact both decrease, as Hcj increases, to approach the coherent rotation mode.
In contrast to the general belief that Spin Reorientation Transitions (SRT) influence to large extent magnetic properties of some cobalt containing ferrites materials, it was observed by the author for the first time that the SRTs also affect the electrical transport properties such as thermopower (S), electrical conductivity (σ) and dielectric constant (ε1), of some hexagonal W-type ferrites. More surprisingly, it was also observed that SRTs are found to influence neither magnetic properties nor electrical properties in the case of SrZnCo-W type ferrites. A qualitative model to explain the observed behaviour is proposed.
A knowledge of the distribution of divalent metallic (Me2+) and trivalent iron (Fe3+) cations among seven different sublattice sites of an hexagonal ferrite with W-type structure is interesting and essential in understanding and arriving at the orientation of the magnetic ions as well as non-magnetic ions. Cation distribution in turn is very useful in understanding the variation of various magnetic and electrical properties with varying dopant's concentration. Therefore, the orientation of the magnetic ions of two hexagonal ferrite systems viz., Sr-Zn-Co and Sr-Zn-Li has been arrived at using saturation magnetization values.
In single crystals of yttrium iron garnet irradiated with an intense visible light at 77 K, a remarkable change of the temperature dependence of complex permeabilities μ' and μ'' is observed. Simultaneously, conspicuous double peaks of photoinduced disaccommodation, DA around 130 K(DA(I)) and 200 K(DA(II))were found, with correlative onset of the irreversible decrease of μ' at low temperature. Activation energies of these peaks are estimated 0.46 eV for DA(I) and 0.7 eV for DA(II). In addition, we observed the third peak(DAIII, 0.88 eV), independent of irradiation around the room temperature. For an explanation of these results, a simple model is presented here for explaining these results.
BiMnO3 synthesized at high pressure is a triclinically distorted perovskite and a ferromagnetic insulator with Tc = 105 K, in contrast to antiferromagnetic LaMnO3. Though the conductivity of Bi1-xSrxMnO3 increased with x, no metallic state was achieved to the solid solution limit of x = 0.67. Furthetmore saturation magnetic moment of 3.6 μB observed in BiMnO3 decreased very rapidly with increasing x, and ferromagnetism disappeared for x > 0.4. These observations suggest that the highly polarizable Bi3+ ion with 6s2 lone pair would cause local distortion of the perovskite lattice, which presumably reduces the mobility of carriers. The ferromagnetism in BiMnO3 cannot be compatible with the double exchange mechanism, but is probably related to the orbital ordering of manganese ions in the perovskite lattice. The ferromagnetic moment of Bi1-xCaxMnO3 appeared in Ca-rich composition of 0.825 < x < 0.95, showing maximum value of 1.1 μB per a Mn atom at x = 0.875. The electrical resistivity remarkably decreases with the Bi substitution, but never shows metallic behavior. The ferromagnetism achieved by electron doping seems to be suppressed by charge ordering with further doping.
Rare earth manganites RMn2O5(R=Nd−Lu, Y or Bi) have been revealed ferroelectric at low temperatures. The spontaneous polarization is along the b-direction of the orthorhombic crystal. The ferroelectric Curie temperature is between 25 K and 39 K, apparently depending on the total orbital quantum number L of the rare earth ion. In several oxides of the series, another phase transition is present at lower temperature, accompanying an remarkable change in spontaneous polarization.
The transformation of the Zn(II)-and Mn(II)-wüstite into spinel-type compound was studied to investigate the effect of foreign cations (Zn(II), Mn(II) ions) on FeO-wüstite disproportionation into α-Fe and Fe3O4 bellow 575°C. In these transformation reactions, the Fe(III) ions in the Zn(II)- and Mn(II)-wüstites (Zn2+xFe2+yFe3+zO, Mn2+xFe2+yFe3+zO, x+y+y<1) form the spinel type structure in Ar gas at 500°C(Zn(II)-wüstite) and 450°C(Mn(II)-wüstite), but no α-Fe phase appeared, indicating that the presence of those foreign cations in the FeO-wüstite interferes with the disproportionation into α-Fe and Fe3O4. No manganese oxides were formed from Mn(II)-wüstite at 450°C, while the ZnO was formed from the Zn(II)-wüstite. This difference came from the fact that the Mn(II) ion does not have a site preferency and Zn(II) ion has a tetrahedral site preferency.
The chalcogenides of 4 - and 5 - component system viz. PbBi1-x Mo2-x, Te2-ySe2-z, Pb2Bi1-x Mo1-x,Te2-y Se2-z Pb2-Bi4-xTe3-y Se4-z and PbBi5-x Te3-y Se4-z have been prepared at 900°C. These compounds crystallize into orthorhombic symmetry. The chemical compositions of these materials are confirmed by EDX. Resistivity studies showed these compounds are semiconducting.
Magnetic interactions in some intermetallic AM2X2 compounds and their solid solutions have been investigated using ac-susceptibility and neutron-diffraction measurements. The materials studied (A = U, Nd, Tb; M = Co, Ni, Cu; X = Si, Ge) have predominantly the tetragonal ThCr2Si2-type crystal structure, and ordered magnetic moments are found only on the A site aligned along the tetragonal axis in ferromagnetic basal planes. The magnetic phase diagrams of the U(M,M')2X2 solid solutions have been determined. The results suggest RKKY-like magnetic interactions in these systems, with variable magnetic structure and oscillatory behaviour of the ordering and paramagnetic Curie temperatures. The relative orientation of ordered A and Ln magnetic moments in the (A,Ln)Co2Ge2 solid solutions have been determined. It is antiparallel for the (U,Tb) and (Nd,Tb) cases and parallel for the (U,Nd) case, in accordance with the "spin-charge" concept.
The resistivity below Tmin of a-Co80-x-yFexMny B12Si8 alloys is investigated. The resistivity data was fitted to a logarithmic temperature dependence and the conducitivity data to a √T dependence. √T dependence gave a better fit. From the coefficient of √T term, the diffusion coefficient D was calculated on the basis of electron-electron interaction effects. D was found to increase with the concentration of Mn. This also indicated that the density of states at the fermi level increases with the addition of Mn in these alloys.
For the granulation of ferrites according to the Vacuum Hot Steam Process (VHSP) a high-pasty material is used as starting material. Homogenizing and dispersing of the mixing components are made in an intensive mixer with rotating mixing pan and high-speed rotor by using high shearing forces. Granulation is made by drying. Superheated steam is passed through the material as drying medium under vacuum. The adjustment of the granule size can be reproduced. The granules are distinguished by an increased density, considerably improved homogeneity, higher abrasive resistance, homogeneous moisture distribution in the interior.
This study investigates the grain growth behavior (normal and abnormal) in Mn-Zn ferrite system with respect to the addition of CaO and SiO2. The powders of (Mn0.76Zn0.24O)0.94(Fe2O3)1.06 composition and average particle size of 0.94 μm are prepared by milling the calcined powder in an attritor. CaO and SiO2 are added in the range from 0 to 1.5 wt%, respectively. In the specimen containing a very low additive content (less than 0.02 wt% CaO and 0.007 wt% SiO2), a typical normal grain growth is observed. In the specimens containing 0.08 wt% CaO and 0.011 wt% SiO2, however, a few grains grow abnormally, while the growth of other grains is almost suppressed. In the specimen of a little more additive content (1.5 wt% CaO and 1.5 wt% SiO2), the grains are faceted in the liquid matrix and abnormal grain structure is developed. The results are discussed on the basis of growth kinetics determined by two-dimensional nucleation at the singluar interfaces of faceted grains.
We have examined the effect of heat treatment temperature and time on magnetic properties of rapidly quenched oxides with compositions close to ZnFe2O4. These oxides show high magnetization even at room temperature as we reported previously. In particular, attention is focused on oxide with nominal composition of 60ZnO•40Fe2O3. It is suggested that the high magnetization is brought about by iron ion clusters with Zn2+ ions occupying octahedral sites as well as solid solution of Fe3O4 in ZnFe2O4. As the heat treatment temperature increases, the room temperature magnetization decreases sluggishly below 500°C and decreases sharply above 600°C when the heat treatment time is 2 h. It is proposed that the decrease of magnetization below 500°C corresponds to disappearance of iron ion clusters while the rapid decrease of magnetization above 600°C is caused by oxidation of Fe2+ to form ZnFe2O4 with normal spinel structure.
We have produced MnZn-ferrite via high-energy ball-milling of the elemental oxides MnO, ZnO, and Fe2O3. X-ray diffraction indicates a pure phase spinel forms after 1250 min. of ball-milling, with all diffraction peaks being indexed to the fd3m space group having a lattice parameter 8.422 Å(8.429Å after 2400 min. milling). Extended x-ray absorption fine structure (EXAFS) analysis reveals that the conversion of metal ions from their elemental oxide structures to the spinel phase occurs nearlinear with milling time with 50% of the oxides converted after approximately 500 minutes. Multiple-scattering EXAFS modeling indicates an increase in the inversion parameter for the milled ferrite with a abnormally high fraction of Zn cations residing on the B sublattice.
With a useful combination of magnetic and electrical properties, Ni0.65 Zn0.35 Fe2 O4 is a desirable composition for power transformer cores in Switched Mode Power Supplies (SMPS). The present investigation is aimed at studying electrical and microstructural aspects of this composition under different sintering conditions. Room temperature DC resistivity of the ferrite has been found to decrease slowly and gradually with an increase either in sintering temperature or in sintering time below the sintering schedule of 1250°C / 2 hrs and for the above the decrease has been observed to be rapid. The observed variations have been attributed to microstructural changes brought about by the sintering conditions. Temperature dependence of resistivity shows two regions thus indicating the presence of atleast two conduction mechanisms in the system. Conclusions have been drawn towards optimisation of sintering schedule required for the development of transformer cores for SMPS applications.
This experiment was carried out to investigate the effect of Na2O and SrO additives on the magnetic and physical properties of SrZn2-W type hexagonal ferrite. The specimens were prepared by the conventional manufacturing methods without the atmosphere control. It was found that the magnetic properties of SrO • 2ZnO8Fe2O3 were considerably improved on adding 1.33wt% Na2O and 0.67wt% SrO after semisintering treatment. The optimum condition of making magnet with suitable properties are as follows : chemical analysis composition: Sr2+0.953Zn2+1.595Na+0.271Fe2+0.080Fe3+16.157O27 ; semisintering condition : 1300°C x 1h in air ; sintering condition : 1250°C x 0.5h in air. The magnetic properties are : Jm = 0.415 T, Jr = 0.375 T, HcJ = 123.4 kA/m, HcB = 118.6 kA/m, (BH)max = 22.8 kJ/m3, Tc = 361°C, HA = 1084 kA/m, KA = 2.25 x 105J/m3 and nB = 33.8μB. The magnetic properties of this compound powder heated at 1100°C after milling are σ5 = 82.9x10-6Wb·m/kg and HcJ = 199 kA/m, and they are useful as the bonded magnet material.
Fe4N powder has been sintered at below the decomposition temperature applying a hipping pressure, and the influence of oxygen content on saturation magnetization of hipped Fe4N has been studied. The hipping temperature was restricted below 500°C, because Fe4N was decomposed at 550°C. The maximum relative density of 97% was obtained for the Fe4N hipped at 500°C under 200MPa. The Fe4N hipped at 450°C under 200MPa revealed the maximum saturation magnetization of 182emu/g with a high relative density of 95%. It was confirmed that the presence of oxygen decreased saturation magnetization of Fe4N. The Vickers hardness was measured as Hv5.5 × 102, and the corrosion resistance was higher than that of steel.
Image of 500G byte hard disk subsystems for personal computer was studied first. This systems require roughly 180 G bit/in.2 in recording density. Problems to accomplish this density were studied in research fields of magnetic heads, recording media and head media interface. Investigation of media switching speed, surface flatness control of media and heads, fine control of grain growth and development of a few nano meter thick protective and lubricant films are considered as critical issues.
Current status is addressed for spin polarized transport such as spin-dependent scattering and spin-dependent tunneling in artificial structured magnetic thin films for spin electronic devices. A theoretical research is also shown for ferromagnetic tunnel junctions, which can be compared to the experiments. A new ferromagnetic tunneling structure is proposed.
In this paper, we review recent progresses in multigigabit-density magnetic recording with an anisotropic magnetoresistive (AMR) head, and then discuss materials challenges in using ferromagnetic (FM), antiferromagnetic (AFM) and hard-magnetic (HM) films for the AMR head. The AMR head is progressively miniaturized to improve track density and signal sensitivity. This miniaturization causes changes in the magnetic and electrical properties of these magnetic films. To perform magnetic recording at beyond 5 Gb/in2, it is crucial to improve the AMR coefficient of the FM film for the use as an AMR layer, and to increase the product of saturation magnetization and electrical resistivity of another FM film for the use as a soft-adjacent layer (SAL). The magnetic properties of currently used AFM and HM films, on the other hand, appear to be still viable for the multigigabit-density magnetic recording. However, complicated magnetic behaviors in the region where the FM films are contacted by the AFM or HM film, must be very well controlled in the head fabrication process.
We investigated the read/write characteristics of Co-doped ferrite disks. We found that the overwrite characteristics strongly depended on the coercive squareness of Co-doped media. Overwrite characteristics were able to be improved to better than -30 dB when S∗ was controlled. The track edge noise of the Co-doped ferrite media written by a conventional narrow gap head was small, as was the on-track noise, and it was independent of recording density. The NLTS (Non-Linear Transition Shift) value for the Co-doped ferrite media at 200 kFRPI is half that for metal medium. The erase band width in the Co-doped media was as narrow as that in metal media. Co-doped ferrite media exhibited excellent low noise characteristics in high recording density.
A study on Co-γFe2O3/NiO perpendicular magnetic anisotropy media was reviewed focusing on their fabrication process, crystallographic and magnetic properties, and recording characteristics. The merits of the media are: (a) easy preparation using reactive sputtering and annealing at lower process temperature than 350°C, (b) perpendicular anisotropy energy as large as 1-3 × 106 erg/cm3 and perpendicular coercivity which is extendable to 6 kOe, (c) superior hardness tolerable for contact recording without overcoat layer, (d) ultra-high-density recording capability, and (e) low media noise.
Co ferrite and Co-Zn ferrite films were deposited on SiO2/Si substrates and quarts disks under various preparation conditions using the facing targets sputtering apparatus and their crystallographic, magnetic and read/write characteristics have been investigated. Co ferrite films deposited at partial oxygen gas pressure Po2 below 0.2 mTorr at various substrate temperature revealed (311) orientation and quasi in-plane magnetic anisotropy. High Ts above 500°C and Po2 of 2.0 mTorr were necessary to obtain well (111) orientation which had isotropic orientation of magnetization and was suitable for high recording density media. On the other hand, Co-Zn ferrite films deposited at Ts up to 250°C and PO2 of 0.01 mTorr had (111) orientation and possessed moderately large 4πMs of about 3.7 kG and almost the same in-plane and perpendicular coercivity of about 2.0 kOe. The (111) oriented Co-Zn ferrite disk exhibited high linear recording density D50 as high as 136 kfrpi.
Ba ferrite films composed of microcrystallites with well c-axis orientation which seem to be suitable for perpendicular magnetic recording media were deposited using various sputtering apparatus and their microstructural and magnetic characteristics were investigated. The bombardment of energetic particles to the film during deposition and the elevation of substrate temperature strongly affected the growth prcess of Ba ferrite crystallites and the increase of perpendicular coercivity. The films deposited using Facing Targets Sputtering apparatus at the substrate temperature as low as 475°C revealed that they were composed of nanocrystallites with the grain size below 100 nm and exhibited the coercivity of as high as 2.3 kOe.
Ba ferrite/Pt bilayered films were deposited on thermally oxidized Si wafers using plasma-free sputtering apparatus and post-annealed at 800°C in air for 15 min, and then, the dependence of crystallographical and magnetic characteristics at the substrate temperature Ts in the range from room temperature to 550°C were investigated. Although Ba ferrite films deposited directly on the substrates revealed random c-axis orientation, the Ba ferrite layer deposited on Pt underlayer at Ts above 200°C and post-annealed revealed excellent c-axis orientation. They exhibited the saturation magnetization 4πMs of 4.2 kG and almost same in-plane and perpendicular coercivity Hc|| and Hc⊥ of 0.7 kOe. The film deposited at Ts above 500°C exhibited 4πMs of 4.6 kG and high Hc⊥ of 1.8 kOe.
Effects of 2 step crystallizing process on magnetic properties, particle size distributions, crystallization mechanism were investigated on the basis of glass crystallization method. First annealing temperature was a definite condition to determine the particle size and the switching field distribution(SFD). Fine particles with average diameter in the range from 30 to 40 nm, having narrower SFD than that obtained from conventional one step crystallizing process, were obtained under certain conditions. Those first annealing conditions changed flakes into mixtures of a non-magnetic amorphous state and nano-meter sized particles which magnetic ordering just began to develop.
Acicular barium ferrite fine particles doped with Co2+ ions and Ti4+ ions were prepared by a conventional sintering method. Magnetic properties and crystal structure of the acicular BaCoXTiXFe12-2X O19 (X=0-1.0) particles were investigated. These particles had long axis of about 0.8μm and aspect ratio of about 11. The size of acicular fine particles did not changed with doping content of Co2+ and Ti4+ ions. The magnetization for the acicular BaCoXTiXFe12-2X O19 particles had same value of about 0.33 Wb/m2, but the coercive force of them was decreased from 310 kA/m to 35 kA/m with increase of doping content. In addition, crystal structure of them were investigated. From x-ray diffraction patterns, the acicular BaCoXTiXFe12-2XO19 particles had hexagonal structure of the magnetoplumbite. It was observed by dark field images of TEM that the acicular BaCoXTiXFe12-2XO19 particle consisted of some crystallites and the c-axis of them were normal to the long axis of an acicular particle.
Co-doped Bi3Fe5O12 garnet films were prepared using two targets (TA = 3Bi2O3-5Fe2O3 and TB = CoFe2O4 or Co metal) by means of reactive alternating ion beam sputtering technique. Co spinel ferrite phase was also observed by X ray diffraction measurement (XRD), even when garnet phase mainly grows. The saturation magnetization showed a peak for the sputtering time ratio R. The coercive force of the films monotonously increased with decrease of R. The films also showed irregular Faraday rotation and magnetization hysteresis loops. The films deposited using CoFe2O4 as Co source formed G phase in the wider range than those deposited using Co metal of CoO. From these phenomena, it turned out that Co ion exists as Co spinel ferrite particles scattered in Bi3Fe5O12 films independent of Co source materials.
The microstructures of ion-beam co-sputtered Co-C thin films were studied. As-deposited films whose carbon concentrations were more than 46 at%, consisted of a granular amorphous phase. Successive annealing transformed these films to crystal phase keeping the granular structure. This procedure fabricated fine Co particles 10 nm in diameter surrounded by graphite boundary.
The coercivity of Co-O obliquely deposited films formed directly on the polymer substrate increases with increasing thickness up to around 40 nm, and decreases over 50 nm. A CoO underlayer makes the coercivity and the uniaxial magnetic anisotropy of the films high owing to an improvement of c-axis orientation of hcp Co. The morphological texture of the under layer is considered to promote the c-axis orientation of the films. The Co-O films are endowed with resolution potential high enough to attain Gbit/inch2 order of areal recording density. The comparison between the Co-O film and hard disk media in the recording properties shows that the Co-O tape has much higher reproduced voltage than the disk for magnetoresistive (MR) reproduction use.
Magneto-optical Faraday effect of bismuth-substituted yttrium iron garnet (Bi:YIG) films with disordered multilayer structures was analyzed theoretically to examine the correlation between the magneto-optical properties and the localization effect of light. The films of interest are composed of Bi:YIG layers and SiO2 layers which are piled up in an arbitrary sequence. The results suggest that a huge enhancement of Faraday rotation angle θF takes place in films with appropriate layered structures for supporting the localization of light: for instance, when the film structure meets the structure of one-dimensional magneto-photonic crystal with a defect, θF reaches more than 160 times larger than that of a Bi:YIG single-layer film.
Magneto-optical recording media with high Kerr rotation at Short wavelengths were successfully obtained in a trilayer form, TbFeCo/NdFeCo/TbFeCo. We optimized the trilayer structures by changing the thickness of the third layer TbFeCo amorphous films on the free surface side. By employing these media, CNR 44dB was obtained at the recording frequency 2.9 MHz by using a laser light of 830 nm wavelength.
The BixDy3-xFe4AlO12 thin films (where x=0∼1.96) were prepared by laser ablation with XeCl laser (λ=308 nm) on the Corning #7059 glass substrates. Single-phase BixDy3-xFe4AlO12 thin films were fabricated by controlling the O2 pressure and substrate temperature during deposition then annealed at 650°C. The effects of deposition parameters and heat-treatment condition on the structure and magnetic properties of films were investigated. In addition, the relationships between the perpendicular magnetic properties of the films and thickness of the films were examined. From XRD analysis, we found that these BixDy3-xFe4AlO12 films were polycrystalline garnet and no preferred orientation. VSM measurement showed that the perpendicular coercivity of the Bi1.58Dy1.42Fe4.04Al0.96O12 film (thickness=100nm) was about 1130 Oe. The magnetic anisotropy of this film was normal to the film plane. This anisotropy was stress induced. The MO-Loop measurement showed that Faraday rotation angle of this film was 0.3 deg/μm for λ=780nm.
The temperature dependent sensitivity characteristics and the linearity error in the zeroth-order diffraction beam from the stripe domain materials of (BiGdY)IG are studied. The contribution of Gd substitution on the improvement of the temperature dependence of sensitivity was clarified. It was found that the origin of the large linearity error in the small magnetic field region is the small domain-wall coercive force of 0.3 Oe.
The authors have conducted magnetization and EXAFS studies on pulsed laser deposited non-equilibrium single crystlline MnZn-ferrite films. The results of this study shows that the magnetization can be significantly enhanced over that of the bulk depending on deposition conditions. EXAF studies show a strong correlation between the Mn and Fe cation site occupation and the resulting magnetization.
Extended x-ray absorption fine structure spectroscopy has been applied to study the cation distribution in a series of non-equilibrium MnZn-ferrite powders and films. We find that the use of high-energy ball-milling of bulk powder ferrites, and variations in oxygen partial pressure in pulsed-laser-deposited thin film ferrites, facilitate a non-equilibrium inversion which in some cases dramatically influences the magnetic properties of these ferrites.
The ultra clean sputtering process (UC-process) was introduced in the fabrication of thin film media and spin valve type Ni-Fe/25at%Ni-Mn/Ni-Fe films to establish the new concept of controlling the microstructure and magnetic properties. The relation between cleanness during film deposition process and magnetic properties has been discussed in connection with their microstructure. The UC-process here presented enables the control of the fine structure of the thin films and resulted in excellent magnetic properties. This study demonstrates that the UC-procss is very superior to the normal process presently used and plays a dominant role for the fhin film media and spin valve head fabrication.
Co-Cr-Ta perpendicular magnetic recording media with Ni-Zn ferrite backlayers are promising candidates to improve high frequency performance in extremely high linear density applications. Though ferrite plating facilitates to fabricate polycrystalline Ni-Zn ferrite films even at low temperature below 100°C, the films have disadvantages of large grain size (200∼300 nm) and roughness (4∼5 nm). Such surface texture caused aggregating grains without clear magnetic isolations in Co-Cr-Ta layers deposited on them, resulting in low perpendicular coercivity Hc⊥ (1.3 kOe). These properties will lead poor recording density characteristics and high media noise. RF sputter-etching of the Ni-Zn ferrite backlayers was attempted in order to improve their surface texture. It reduced grain size (30∼50 nm), and increased Hc⊥ (3.0 kOe) in the Co-Cr-Ta layers, presumably through a reduction of surface roughness and a formation of many fine nodules on the Ni-Zn ferrite-plated backlayers, which play a role of nucleation sites for the Co-Cr-Ta grains.
The characterization of NiCuZn Ferrite (NCZF) slurry and green sheet using a water mixed medium system has been studied. The raw materials and the NCZF powder were ground by wet ball milling with the 0.7wt% polyacrylic ammonium salt. The 21vol% of NCZF slurry was prepared by a ball milling. The polyacrylic vinyl copolymer (Mw; 60000) was used as a binder. The mixture of distilled water, Isopropyl alcohol (IPA) and 2-butoxyethanol was used as a dispersion medium. The water content of medium varied from about 40% to 80%. The NCZF slurry was characterized with the water content. The microstructure and the mechanical property of the NCZF sheet have been investigated.