Media for high density magnetic recording

Longitudinal recording is limited at high bit densities by recording demagnetization, self-demagnetization, and adjacent-bit demagnetization, which occur during the writing-demagnetization processes. To minimize these adverse effects it becomes necessary to resort to extreme scaling of the media parameters and their thickness, with the consequence of greatly increasing the difficulty of fabrication and the cost of such optimized media. Pure perpendicular recording circumvents these writing and demagnetization problems because of the strong head coupling of a single pole head with a double layer medium, positive interaction between adjacent bits, and low self-demagnetization at high bit densities. Therefore, it does not require any extreme scaling of the media magnetic parameters and their thickness. Of great interest, at least for the next several years, are the quasi-perpendicular particulate media which can support perpendicular magnetization. These include the isotropic, high-squareness media, and oriented perpendicular media employing particles with uniaxial crystalline or shape anisotropies. The attractiveness of these media derives from their excellent recording performance and from the fact that they preserve the existing head/media interface and they utilize existing coating facilities which should reflect favorably on their cost. In this paper the advantages and disadvantages of the various media under development for high density magnetic recording are compared, and predictions are made for their potential application in future systems.     

Particulate magnetic recording media: a review

After describing briefly the principles of magnetic recording and the manufacture of media, the author reviews the history, characteristics, and development trends of the most important particulate magnetic recording materials. These are acicular iron oxides, chromium dioxide, cobalt-modified iron oxides, acicular metal particles, and barium ferrite. A trend common to most of the materials is particle size reduction     

The DORF effect: Magnetization ripple in particulate media

In 1966, Pearce [1] introduced without analysis the DORF Effect (DisOrientation by Reverse Field) in liquid dispersions of acicular magnetic particles. Bate and Dunn [2] modified orientation magnets to circumvent the effect and produce recording tapes with improved orientation. This paper describes studies of the DORF Effect and analyzes the behavior of particle groups in liquid media when a reverse field is applied. Magnetization reversal occurs by particle group rotation through a symmetric fanning mechanism which shares features with the magnetization ripple phenomenon [3,4] in continuous metal films. The critical field for particle disorientation follows a dipole-dipole interaction relation like that discussed by Jacobs and Bean [5]. For gamma ferric oxide, critical fields are distributed over the range from 20 to 100 Oe. Rotating sample magnetometer data show the DORF Effect is a destruction of uniaxial anisotropy without creation of biaxial or other anisotropies. Hysteresis work in liquid samples is almost totally due to friction between moving particles.     

Orientation of magnetic particles in a recording medium

The theory of the motion of magnetic particles in a viscous Newtonian medium, first outlined by Newman and Yar-brough, has been extended to include both low and high field orientation modes. It is shown that the equations of motion can be solved analytically, i.e., without resort to numerical integration. The results of the analysis are used to predict values for easily measured parameters of recording media, such as the initial remanence ratio and squareness ratio.     

The origin of magnetic birefringence and dichroism in magnetic fluids

The optical birefringence and dichroism observed in magnetic fluids when subjected to a magnetic field are generally ascribed to orientation of the particles, to anisotropic spatial ordering, or to string formation. Magnitude, concentration- and time dependence of the anisotropies predicted by these mechanisms are compared with the available experimental data. This leads to the conclusion that orientation of small aggregates and secondary aggregation of large aggregates into strings are the most likely cause of the large anisotropies. Orientation of single particles can be responsible for small anisotropies only. Field-induced spatial ordering has, at least optically, not (yet) been observed.     

磁记录用磁性颗粒的临界尺寸及其影响因素

信息存储用磁性介质的记录面密度的不断提高,主要途径之一就是减小磁性颗粒的尺寸.但当磁性粒子减小到一定尺寸后,其磁化方向极易改变(超顺磁性),使所记录的信息丢失,不能再用于磁记录.因此降低磁性颗粒的临界尺寸并提高其热稳定性是信息记录高密度化的关键.就磁记录用磁性颗粒的临界尺寸及其主要影响因素进行了论述.     

Characteristics of barium ferrite tape for magnetic contactduplication

The magnetic properties and electromagnetic characteristics of Ba-ferrite tape for R-DAT magnetic contact duplication (MCD) were investigated. The tapes employed Ba-ferrite particles averaging 0.06 μm in diameter with an aspect ratio between 4 and 5. Ba-ferrite tapes were prepared with perpendicular, longitudinal, and no orientation, and their MCD and ring-head recording (RHR) characteristics were compared. Several distinctive characteristics were observed in MCD, and the desirability of perpendicular orientation at short wavelengths in MCD applications is clear. Tilted orientation was also investigated, and its output level was similar to that of perpendicular orientation in MCD, while in RHR it proved superior to perpendicular orientation in the short wavelength region. The magnetization mode of the slave tape was studied by waveform analysis using the FFT method and in conjunction with the tapes' magnetic properties, such as uniaxial anisotropy energy, remanence coercivity, and squareness ratio     

FePt nanocluster films for high-density magnetic recording

High anisotropy L1(0) ordered FePt thin films are considered to have high potential for use as high areal density recording media, beyond 1 Tera bit/in2. In this paper, we review recent results on the synthesis and magnetic properties of L1(0) FePt nanocomposite films. Several fabrication methods have been developed to produce high-anisotropy FePt films: epitaxial and non-epitaxial growth of (001)-oriented FePt:X (X = Au, Ag, Cu, C, etc.) composite films that might be used for perpendicular media; monodispersed FePt nanocluster-assembled films grown with a gas-aggregation technique and having uniform cluster size and narrow size distribution; self-assembled FePt particles prepared with chemical synthesis by reduction/decomposition techniques, etc. The magnetic properties are controllable through variations in the nanocluster properties and nanostructure. FePt and related films show promise for development as heat-assisted magnetic recording media at extremely high areal densities. The self-assembled FePt arrays show potential for approaching the ultimate goal of single-grain-per-bit patterned media.     

Remanence properties of substituted Ba-ferrite particles for highdensity 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-γ-Fe₂O₃ samples, even though the squareness ratios (SR) of some of the BaF samples were smaller than those of the Co-γ-Fe₂O₃ samples. It Is the small MRD, SFD_r, IRS and large DH _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     

A survey of recent advances in magnetic recording materials

Magnetic recording coatings are still made predominantly of iron oxide particles but the newer particles are significantly better in magnetic properties, dispersibility and orientability than the particles used, say, ten years ago. Chromium dioxide particles show excellent recording performance (particularly at densities above 1000 flux changes per millimeter) but they are presently being challenged by the new cobalt-modified iron oxides. These are formed by diffusing cobalt into the surface of acicular iron oxide particles and it is claimed that the particles prepared in this way are much more stable with respect to temperature and stress than the older cobalt-substituted iron oxides. Metal particles, by virtue of their high moment density and high coercivity, would be ideal for high density recording if they could be passivated permanently. The paper reviews improvements which have been made within the last nine years in the properties of particles for magnetic recording applications and discusses how the improvements were effected.     

Preparation and hard magnetic properties of Co-Zn-P films for high-density recording

The digital recording density of magnetic media can be improved by the development of thin ferromagnetic coatings having a high coercive force. An experimental study of the influence of zinc on the coercive force of chemically reduced cobalt-phosphorus films is presented. Incorporation of zinc increases the coercive force of cobalt-phosphorus films on Mylar substrates by a factor of 2 to 60. Cobalt-zinc-phosphorus films exhibited coercivities ranging from 300 to 1200 Oe, depending on the preparation conditions. The influence of substrate and solution parameters, such as hypophosphite ion concentration, zinc concentration, and pH are discussed with respect to the hysteresis properties of the films. The influence of zinc on the coercivity is attributed to increased magnetic isolation of the cobalt particles and to a modification of particle size.     

Geometric effects in the magnetic recording process

A simplified view of magnetic recording is presented in which the effect of head-medium geometry is clearly exhibited. The model is applied to contact recording with a ring head on thick particulate media. Demagnetization fields are neglected and identical particles with angularly invariant switching fields are considered with various orientation distributions in the recording plane. For all orientation distributions symmetric about the longitudinal direction the longitudinal magnetization component vanishes at the head surface and increases with depth into the medium. Conversely, the vertical component is maximum at the head surface and decreases with depth. The resulting recording spectra therefore have greater magnitudes for vertically well-oriented particles and isotropic distributions of particles with biaxial symmetry. At short wavelengths these distributions give approximately 5 dB more output than longitudinally well-oriented media. The depth variation of longitudinal magnetization also provides one explanation for the peak in the short wavelength input-output curve measured on longitudinal media. These conclusions are expected to be dependent on the assumed angular variation of the particle nucleation field.     

Magnetic properties of new (NP) hydrothermal particles

A new type of uniaxial particles for magnetic recording whose precursors are produced via an original hydrothermal process was recently introduced in the market. The characterizing feature of these materials is their extremely uniform size and ellipsoidal shape. Most of their properties can be ascribed to the lack of external (pores, dendrites, sharp edges) as well as internal (because of ellipsoidal shape) - self-demagnetizing sources, which suggests the name of "Non-Polar (NP)" particles. As a result of this morphology, they show unique magnetic properties. The magnetization reversal mechanism is not accounted for by any known mechanism as fanning or curling and the rotational hysteresis gives very sharp Wrvs. H curves with the lowest values for the integral ever measured for particulate media. The behaviour of coercivity versus packing fraction for Cobalt-surface-modified NP particles is described by a new "constricted magnetization" model. The reasons for these unique characteristics and the practical impact that these materials may have in the field of magnetic recording are discussed.     

Media limitations on achievement of maximum detection window

The recording performance of a digital recording system is primarily dependent upon the isolated half pulse width (T50), signal amplitude, intersymbol interference (ISI), signal to noise ratio (SNR) and the horizontal detection window margin (Tm). These characteristics are related to the thickness and magnetic properties of the media, as well as the head/media interface. This paper addresses the relationship of the media characteristics in longitudinal digital magnetic recording for both particulate and thin film media to the overall recording system performance. The results are shown to proceed from further development of the quasi-optimum time containment filter analysis for media noise dominant and electronic (white) noise dominant recording channels [1], [2].     

Recommendation of a simple and universally applicable method for measuring the switching field distribution of magneting recording media

The most common methods for assessing the switching field distribution (SFD) of magnetic recording media are compared for samples of acicular magnetic particles made of different types of magnetic materials and having various degrees of particle orientation. It is shown that the method of using the maximum slopedM/dH = M_{R}/H_{c}(1-S*)atM = 0of the magnetic hysteresis loopM(H)can be used to characterize SFD of the irreversible magnetization processes which correlate to the recording performance. Thus, (1-S*) is recommended as the most easily accessible and universally applicable figure of merit for SFD.     

Synthesis of nano-sized spherical barium-strontium ferrite particles

Magnetic recording media requires good particle dispersion, a smooth surface, and small interparticle interaction to make an adequate signal-to-noise ratio (SNR). Well dispersed 50-60 nm sized spherical barium-strontium ferrite (S-Ba/Sr-Fe) nanoparticles were successfully prepared with 40 nm sized hematite precursor particles and BaCO/sub 3//SrCO/sub 3/ colloid. The coercivity and saturation magnetizations of S-Ba/Sr-Fe nano-particles were 1568 Oe and 48.6 emu/g, respectively. In order to evaluate magnetic interaction, magnetic tape was prepared using an Eiger mill with binder and organic solvent. /spl Delta/M measurement showed the S-Ba/Sr-Fe nanoparticles in the tape had negative magnetic particle-to-particle interaction.     

Surface properties of Co-γFe2O3particles for digital recording

Commercial cobalt-iron-oxide particles for digital applications have been examined by several techniques: physisorption, mercury porosimetry, and electron microscopy. Surface properties, in particular acicularity and heterogeneity, are related to the rheological behavior of the powders, to their magnetic characteristics, to the characteristics of draw-down coatings, and to the response of experimental floppy disks at predetermined recording frequencies. Particles showing high and uniform dispersibility have a narrow particle size distribution and a relatively large number of high-energy sites     

Properties, preparation, advances and limitations of materials andmedia for perpendicular recording

The trends in perpendicular magnetic recording research are discussed, with emphasis on clarifying the trend of research on recording media, their materials, and head materials. Among numerous proposed perpendicular recording media materials, barium ferrite powder and evaporated Co-Cr films seem to lead in practical applications, since their mass production seems to be very successful. There still exist crucial points in their development. However, improvements are continuously taking place. Other candidate perpendicular recording media for a device which has a ring head are also discussed. It is concluded that, for future high-density magnetic recording, utilizing fully the perpendicular component of media magnetization will furnish the key to success     

A contribution to the investigation of fine-particle solid solutions between cubic iron sesquioxide γFe2O3and cobalt ferrite CoFe2O4

The authors give the chemical, morphological, crystallographic, and magnetic properties of solid solutions between cubic iron sesquioxide γFe2O3and cobalt ferrite CoFe2O4obtained as fine particles by a new preparation method. This method gives the whole range of compositions and allows shifting of the magnetic and morphological features in a direction suitable for magnetic recording applications.     

Rod-shaped polyaniline-barium ferrite nanocomposite: preparation, characterization and properties

Rod-shaped polyaniline (PANI)-barium ferrite nanocomposite was synthesized by in situ polymerization of aniline in the presence of BaFe(12)O(19) nanoparticles with diameters of 60-80?nm. The structure, morphology and properties of the nanocomposite were measured using powder x-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, transmission electron microscopy and vibrating sample magnetometry. Different ferrite/PANI ratios were selected in order to study magnetic and conductive properties. The results indicated that there were some interactions between PANI chains and ferrite particles. The saturation magnetization and the coercivity varied with the ferrite content. The conductivity at room temperature decreased from 43.35 to 6.9 × 10(-2)?S?cm(-1) when the ferrite content changed from 0 to 50?wt%. The composite has excellent electromagnetic parameters which indicates potential application in high performance adsorbing materials in broadband and high frequency ranges. The polymerization mechanism and interactions in the nanocomposites were also studied.