Maximum recording density obtainable in particulate media

The perpendicularly oriented crystal structure conditions of electroless plated film for high density perpendicular recording media were investigated mainly by (002) plane rocking curves and cross sectional SEM observation. A highly oriented narrow dispersion of c‐axis orientation normal to the surface plane was consequently obtained, and the columnar structure of hcp crystal with ca. 0.05 μm diam was confirmed. As a result of preparing disks A and B, which were chemically plated from an optimum bath and a more improved bath, respectively, the recording characteristics with a combination of ring head were obtained as recording densities of for disk A and 25,000 FRPI for disk B, in spite of a relatively thick magnetic medium. The di‐pulse waveforms, which are characterized with perpendicular recording, were observed at low bit recording density. It was indicated by the above results that the chemically plated Co alloy films are applicable as a perpendicular recording medium.

Perpendicular magnetic recording — progress and prospects

Although there is a necessity to achieve excellent overwrite (O/W) in magnetic disk write‐read equipment, the O/W mechanism has not been clarified sufficiently. Accordingly, the investigation of the O/W mechanism by experiment and by a finite element method simulation incorporating a magnetization model has clarified that during O/W, not only the field of the head but also the field generated by the magnetization distribution of the medium (inside field) and rewrite action exert influence on O/W characteristics. From the fact that the inside field changes with the recording density of the signal, modeling was done on the write density dependence of O/W characteristics and verification was made by simulation and experiment.Moreover, from the viewpoint of O/W, a comparison was made of perpendicular magnetic recording and longitudinal magnetic recording. As a result, for the combination of ring head and longitudinal film medium, although the O/W characteristics are degraded with the increase of the O/W signal recording density, in perpendicular magnetic recording the experimental result that the O/W erased value takes a maximum value when the recording density of the overwrite signal is half that of the prerecorded signal in perpendicular magnetic recording is obtained. Thus, it became possible to clarify the mechanism by using a model taking into consideration the inside field.

Perpendicular magnetic recording has a possibility of solving the thermal stability of a recording medium[ll. But noise of perpendicular recording medium must be much more reduced to attain over 20 Hb.in2 recording density.

Medium noise characteristics and transition jitter in perpendicular magnetic recording are explored using micromagnetic simulation. A noise plateau for intermediate recording densities is observed for a recording layer of typical magnetization. The plateau is replaced by a normal linear dependence of noise on recording density for a low magnetization recording layer. We show analytically that a source of the plateau is similar to that producing the non-linear transition shift of signal. In particular, magnetostatic effects are predicted to produce positive correlation of jitter and thus negative correlation of noise at the densities associated with the plateau.

Perpendicular magnetic recording tapes suitable for ring heads

The feasibility of high track density recording in a perpendicular magnetic recording system has been investigated. The properties of the magnetic field of a single pole type (SPT) head having a narrow track width were studied by using a large scale model of a head and a medium. The y-field gradient of the SPT head near the track edge is steeper than the x-field gradient of a ring head, and it was confirmed by Bitter technique that the recorded track width acculately coincides with the width of the main pole of the SPT head. Perpendicular recording using the SPT head also has superior off-track characteristics and the crosstalk signal is hardly detected even at very narrow track pitches. From a magnetics point of view, no problems exist in narrowing the track width of the SPT head in perpendicular recording. Narrow track recording and reproducing with SPT head of only 6.5 μm in track width could be achieved with sufficient signal to noise ratio in perpendicular flexible disk systems.

We developed a new component level thermal decay test that directly measures decays in media signal and noise, which are combined to obtain signal-to-noise ratio (SNR) decay. The SNR decay on spin stand is in good agreement with the hard disk drive bit error rate decay data. The effect of recording linear density (KFCI) on the SNR decay is studied, which is mainly attributed to the demagnetization field change with the recording density. Applying this test to a group of media with a broad range of nucleation field (Hn), it is found that the SNR decay correlates better with the Hn than with the thermal stability factor (KuV/kBT). For a perpendicular magnetic recording media with Hn∼−2000 Oe exhibits zero SNR decay, it indicates strong robustness thermal stability.

A thin film head of new probe type was fabricated, applicable to perpendicular recording on Co-Cr rigid disks. The head consists of a magnetic film for the main pole and multiturn spiral coils (2 layers, 10 turns) were fabricated on a ferrite substrate. The recording characteristics were measured on 14-in. sputtered Co-Cr disks having a high permeable Ni-Fe back layer. The magnetomotive force for saturation recording was 2 A-T and the output voltage was 0.65 mV at a pole thickness of 4 μm and pole width of 70 μm, at a head to medium spacing of 0.3 μm. The recording density was measured to be 17 kFRPI at a pole thickness of 0.7 μm.

High linear recording density by combining a single‐pole magnetic head and Co‐Cr/Ni‐Fe double‐layer medium in a perpendicular magnetic recording hard disk drive is discussed. The present perpendicular magnetic recording system adopts a sliding contact head‐disk interface suitable for high‐density recording. A spacing as small as 30 nm between a head and a medium is obtained, measured by an optical interference method. Attaining such a small spacing promises superiority of the sliding contact head.An attempt is made to fabricate a composite head (= separate configuration of read/write head) to realize high resolution. This composite head is designed to maintain an important feature of saturation recording in the perpendicular magnetic recording scheme.A computer simulation analysis of the head‐disk interaction shows that a stronger interaction gives rise to a better resolution for a single‐pole head. In view of those results, heads and media with various Co‐Cr thicknesses are fabricated. A high D50 value of 170 kFRPI and a good overwrite performance better than ‐30 dB are demonstrated.

The head media integration played a very important role to push up the areal density of perpendicular recording successfully. Besides the success of good sensitivity and high resolution reader at desired feature size of recording bit, the advanced writing process is the key enabler to sustain the areal density growth continuously. The sharper field gradient of writer and the narrower switching field distribution of recording media improve the transition jitter and promote the SNR of recording media. Without reducing grain size, the areal density of perpendicular recording has been increased by a few times. In this work, we investigate the performance of writing process via the measurement of head field footprint in recording media on the Spinstand. The feature size variations of head footprint at different writing current and different flying height (FH) illustrate the effective writing process visually. The transition curvature with transition width value at the trailing edge of writer pole is the key indicator to show the linear density capability related to writing process.

Adjacent-track interference in ultrahigh-density perpendicular recording system

Magnetic recording properties of electrolessly deposited NiXP/CoReNiMnP double layer media

Kinetics of magnetization reversal and dynamics of domain walls in thin La0:7Sr0:3MnO3 manganite films are studied by magnetooptic visualization technique. Two types of magnetic domain structure are revealed in 20 nm thin film, namely, the small-scale patched domains with perpendicular magnetization, which are formed after zero field cooling, and wide macro-domains with an in-plane magnetization, which appear as a remnant state after saturation by the field of any orientation. The following magnetization reversal is found to occur via the nucleation and thermoactivated motion of the 1800 domain walls. Strong temperature dependence of dynamic parameters is established near the room temperature. A heating of 10 K above 294 K results in 1.5 reduction of coercivity, in alteration of magnetic permeability, magnetic viscosity and activation volume by order of magnitude. The obtained results could be explained taking into account magnetic after-effects specific for materials with the magnetic ions of transient valence.

Debye's theory of polar molecules has been extended to give simple expressions for conditions of maximum loss per cycle in terms of equivalent circuit bridge or substitution measurements. The dielectric loss in a good grade of viscous mineral insulating oil has been separated into two components; one resulting from conduction, and the other showing characteristics with frequency and temperature qualitatively explained on the basis of the presence of polar molecules in the oil. A quantitative check shows the order of magnitude of this second loss to be the same as that which would be predicted by Debye's theory. The experimental curve shows a wider frequency response than the theoretical curve, indicating that the simple theory is not sufficient to account for the observed data. This may result from the presence of polar molecules of many different sizes giving an average response rather than molecules of one size only, as assumed in the theory. The size of the polar molecules necessary to give the observed effects was calculated from Deybe's theory and found to be of the right order of magnitude. Data taken over a wide range of frequency and temperature indicate the danger in drawing conclusions as to the characteristics of a material from data taken for limited ranges of experimental conditions. The curves show that either in-increasing or decreasing power factor can be obtained as a function of either frequency or temperature for certain narrow limits of experimental conditions. The dielectric loss in good commercial mineral insulating oils at power frequencies and operating temperatures results from conduction only, the contribution of polar molecules to the loss being negligible. Before a definite statement is made regarding the mechanism of the observed loss, studies should be made to determine whether a satisfactory theory can be developed which is based only on the motion of charged particles in a viscous medium.