Comments on "An analysis of tilted magnetic transition in magnetic transitions in magnetic recording media"

Expressions for the demagnetizing field caused by the surface magnetic charge produced by vertical magnetization in a tilted transition are presented. This field should be added to that used by Chang and Perez in their analysis of tilted transitions.     

An approach to recording on tilted media

A simple model for recording on media with a tilted anisotropy axis is proposed. The model combines the slope theory (Williams and Comstock model) with vectorial aspects of the head fields, their corresponding gradients and the angular dependence of the switching fields of the medium. In the case of obliquely deposited metal evaporated tape, the model is shown to predict the experimental data correctly     

An analytical model for the recording of transitions in thin magnetic recording media with linearized hysteresis loops

Analytical expressions are derived for the magnetization distributions recorded in thin-film recording media possessing "linear' hysteresis loops. The results are presented in a form somewhat familiar to workers in this field.     

Barium ferrite magnetic recording media

Barium ferrite particulate media have generated a lot of interest for advanced magnetic recording applications because they offer the potential to combine high recording densities with relatively low manufacturing cost. They consist of small (sub-tenth micron) plateletshaped particles with competing orthogonal anisotropies (crystalline and shape) of comparable magnitude. These anisotropies, along with the quasi-perpendicular characteristics of the barium ferrite coatings impart to them many subtle and surprising properties, requiring a careful and judicious choice of parameters for each application. The choices include the aspect ratio of the particles, their coercivity, the particle-to-binder loading, and the degree and direction of magnetic orientation. The problem areas include dispersion and orientation of the particles, overwrite characteristics of the coatings, thermal coefficients of the magnetic parameters and maintaining media coercivities at moderate levels. I this paper, we discuss the effect of the particle and coating parameters on the ensuing magnetic and recording properties of the media, and the types of choices that should be made to minimize the impact of some of the potential problems mentioned above.     

Eddy currents in conducting magnetic recording media

Use of metallic magnetic recording media raises the possibility that medium eddy currents will influence the recording process. The mathematical analog to diffusion of heat allows exact solutions for cases approximating those of interest. Eddy current effects are shown to be negligible for usual thicknesses of longitudinal and perpendicular media.     

Composite media for perpendicular magnetic recording

A composite perpendicular recording media consisting of magnetically hard and soft regions within each grain is proposed. Application of applied field initially causes the magnetization of the soft region to rotate and, thus, change the angle of the effective field applied to the hard region. This important change in the effective field is enabled by an exchange layer that moderates the interaction between the two regions. Energy arguments show that the resulting performance (as measured by the ratio of energy barrier to switching field) is similar to the previously proposed tilted media, while avoiding some of the difficulties. In particular, fabrication of the proposed composite media appears to be significantly easier than that of tilted media.     

Perpendicular magnetic recording performance of double-layer media

Perpendicular magnetic recording performance for double-layer (Co-Cr,Ni-Fe) media was analyzed, with a simple magnetization model, in comparison with single-layer media. The calculated output voltage from a ring-shaped reproducing head shows good agreement with experimental data. It is shown theoretically and empirically that the Co-Cr layer thickness can be reduced without sacrificing the output amplitude, if the Ni-Fe layer is placed underneath it to perform as a "flux sink" to extinguish the rear surface charge on the Co-Cr layer.     

Wear properties of perpendicular magnetic recording media

Wear properties of sputtered Co-Cr/permalloy double layer on flexible substrate with and without an inorganic protective top layer were studied under simulated tribological conditions. A soft head slider (ex. glass) gave even severer damage to media than the hard one (ex. Al2O3-TiC), and a 200 Å thin inorganic protective top layer was effective enough to enhance resistance against wear. Read-write experiments were also done with use of the double layer flexible media with the protective top layer (200 Å in thickness) by running them on a specially designed driver unit with an Al2O3.TiC spherical SPT head. An out-put signal loss was no more than 3dB even after 10 million times of the head passes.     

Scanning transmission electron microscopy analysis of grain structure in perpendicular magnetic recording media

The key component of a hard disk medium is a Co-based magnetic layer (ML) grown on a Ru seed layer. The ML nanostructure, composed of less than 10 nm grains, is believed to be controlled by this seed layer. We successfully used scanning transmission electron microscopy energy dispersive spectrometry simultaneous composition-based imaging and Moire? pattern analysis for determining the mutual structural and orientation relationship between the two layers revealing a grain-to-grain agreement. The method presented here can be utilized for observing structural correlations between consecutive polycrystalline thin film layers in general.     

Nanocomposite magnetic films for high-density perpendicular magnetic recording media

Multi-layer nanocomposite structures of Ta/Ru/CoCr₁/FeCoTaCr(soft magnetic layer)/CoCr₂/CoCrPt-SiO₂(hard magnetic layer or recording layer)/C and Ta/Ru/CoCr₁/CoCrPt-SiO₂/CoCr₂/FeCoTaCr/C were proposed. This exchange coupled composite (ECC) media consisting of hard/soft stacked magnetic layers were promising in improving the writability of perpendicular magnetic recording media. A small CoCrPt c-axis orientation dispersion of about 3° was achieved with the optimized sputter conditions. The CoCrPt-SiO₂ grains were well segregated by SiO₂ at grain boundaries. The macro-magnetic properties showed that the stacked magnetic grains switched in a coherent mode and that switching field decreased with increasing the thickness of the soft magnetic layer.     

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     

Fabrication of magnetic nanodot arrays for patterned magnetic recording media

Fabrication processes of arrayed magnetic nanodots for the use of patterned magnetic recording media were reviewed. One candidate for the patterned media is ordered assemble of magnetic nanoparticles, and the other is patterned magnetic thin films fabricated using various micro/nano scale machining processes. For the formation of patterned masks and molds, lithography processes as well as self-organized pattern formation are utilized. For the deposition processes of magnetic dots, electrochemical deposition processes were widely used. These fabrication processes are reviewed mainly from recent reports. The recording systems for the patterned media including probe-type-recording are also overviewed.     

Spatial noise phenomena of longitudinal magnetic recording media

The authors have studied the spatial noise characteristics of uniformly magnetized media and implemented a synchronous magnetic pulse detection technique to measure waveforms from precise radial and azimuthal locations on a magnetically recorded disk. They introduce a correlation analysis which includes measuring noise waveforms from the same position on the disk under different remanent magnetic states. Results from this analysis demonstrate that at remanence only minor changes occur in the output waveform and its (presumed) corresponding magnetic structure from write to write, while at DC demagnetization large variations are seen for successive writes. This sensitive correlation technique is used to analyze the random and deterministic components of media and head noise     

Temperature dependent magnetic properties of barium-ferritethin-film recording media

Temperature dependencies of magnetic properties were measured in barium-ferrite thin films with grains having in-plane aligned as well as randomly oriented easy axes. The temperature dependence of H_c was shown to be similar to that of the effective anisotropy field, which is determined by the crystalline and shape anisotropies. The measured H _c values in the easy-axis aligned and randomly oriented films are significantly smaller than those predicted by the Stoner-Wohlfarth (SW) coherent rotation model. Such discrepancies are believed to be caused by incoherent rotation. Deviations from the SW model were also found within a wide temperature range in the angular dependence of coercivity and remanent coercivity, the field dependence of torque and rotational hysteresis. These led to the conclusion that temperature has only weak affects on the rotation mode of the magnetization. The discrepancies between the thermal activation volume and the grain size which were found previously at room temperature, and were believed to be yet another signature of incoherent rotation, were shown to also exist at a low temperature of 173 K     

Theoretical study on stress-induced demagnetization in magnetic recording media

A simple and fundamental model of stress-induced demagnetization, which has scarcely been analyzed theoretically, is presented. Stress-induced demagnetization in a magnetic recording medium results from the magnetization reversal of individual magnetic particles dispersed in the magnetic layer. The magnetoelastic energy due to the application of three-dimensional stresses and the magnetostatic energy due to the demagnetizing field must be taken into account for an investigation of the magnetization reversal of each particle. It is found that the magnetization reversal can take place even during small stresses if a sufficient demagnetizing field exists. The sign of the magnetostrictive coefficient λ100has a significant relation to the susceptibility of magnetization reversal.     

Noise in high performance thin-film longitudinal magnetic recording media

The problem of noise in thin-film longitudinal media is analyzed experimentally and theoretically. The physical mechanism for the noise is shown to be fluctuations in the geometry of the zig-zag transitions separating bit cells. The shifted-transition noise model is introduced as a means of quantifying the noise processes. Spatial, spectral, and autocorrelation properties are introduced. A calculation of the RMS noise voltage yields the characteristic noise versus density curves found experimentally, and clarifies their interpretation with respect to the signal-to-noise ratio. The corresponding experimental data for several plated and sputtered media are presented and analyzed in the light of the model predictions.     

Self-consistently computed magnetization patterns in thin magnetic recording media

A model involving head motion is given for self-consistently computing magnetic recording medium magnetization patterns. The reduction in demagnetizing field due to the presence of the high-permeability head structure is included, as is record head removal, read head replacement, and computation of the readback voltage. The model is capable of handling an arbitrary record current waveform. Optimum record-current amplitude for nonreturn to zero (NRZ) digital recording is first determined, and then single-, double-, and quadruple-transition computations are performed using two different values of hysteresis loop squarenessM_{r}/M_{s}and both linear and exponential current reversals. Results are primarily for the Karlquist fringe field, but the recording properties of a head exhibiting regions in which the fringe field reverses sign are also briefly investigated.     

Thermal stability improvement for longitudinal magnetic recording media

This paper reports and discusses the effects of M/sub r/t cancellation and bottom/top magnetic layer thickness ratio on thermal stability and recording characteristics of low-noise synthetic antiferromagnetic (SAF) longitudinal recording media. It is shown that by proper design and process, SAF media with low M/sub r/t cancellation can deliver excellent overall recording performance with acceptable thermal stability. We present a unique approach to significantly improve the thermal stability of SAF media with low M/sub r/t cancellation by adjusting the bottom/top magnetic layer thickness ratio. Increasing the bottom/top magnetic layer thickness ratio significantly improves amplitude decay rate and media coercivity temperature dependence with little sacrifice in recording performance.     

Calculation of the switching constant of magnetic recording media

We studied the dynamic switching time in two classes of media by considering two different particle orientation distribution functions. We calculated the switching constant directly from the Landau-Lifshitz-Gilbert equation of motion, which was chosen to simulate the dynamic properties of the media. A strong linear relation between the reciprocal of the switching time and the difference between the applied and anisotropy fields is illustrated. In media for which experimental results are available, the values we obtained here agree within a factor of 2