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To enable the smaller slider-disk spacing that is required for the continual increase in data storage density, the interaction between the slider and the lubricant layer must be understood. In this paper, an interesting experimental phenomenon of sudden lubricant droplet transfer from the slider to the disk is reported and investigated. This phenomenon is different from the lubricant moguls and ripples previous researchers have identified. Is it expected that this sudden lubricant drop-off will degrade head-disk spacing and magnetic signal. Therefore, it is imperative to understand the mechanism and the driving conditions so that it can be prevented. Index Terms--Flyability, fly-height modulation, head-disk interface, lubricant.

This paper is an attempt to review some historical trends in thin film disk lubricant technology, and the associated requirements in terms of overall reliability, as we inexorably approach the subnanometer clearance mark. We will mainly focus on the physical attributes of the lubricant, and more particularly on the slider-induced effects on lubricant dynamics. Design attributes for subnanometer clearance will be discussed in this historical context, as qualitative to semiquantitative models have emerged that allow such extrapolation. Index Terms--Clearance, head-disk interface, lubrication.

Perfluoropolyether lubricant films on magnetic disks were observed by means of atomic force microscopy (AFM) with a fluoride-coated probe. The lubricant films could be observed directly because the adhesion force was decreased by the anti-wetting effect of the fluoride coating on the probes. We compared the molecular conformation of Z-dol (Mw: 2000, 3000, 6000, 8000) with that of Z-tetraol. Thus, we found that the film coverage of a lubricant with high molecular weight exhibited varying (i.e., higher and lower) step heights of the lubricant film boundary. The Z-tetraol film exhibited higher coverage and the higher step height as compared to Z-dol2000. To further study the step height measured by means of atomic force microscopy, we compared the step height with the shoulder height of the spreading profiles of the films. The step heights were almost equal to the shoulder height. We observed the lubricant film after shearing by using contact scanning mode atomic force microscopy. The coverage of the sheared lubricant film increased higher than the initial coverage before shearing. Subsequently, the lubricant molecular conformation was varied due to the shearing, and the coverage was increased. Index Terms--Atomic force microscope, lubricant, magnetic disk, perfluoropolyether.

This paper deals with the experimental identification of elastic, damping and adhesion forces in the dynamic collision of a spherical slider with a stationary magnetic disk. We used rough [Al.sub.2] [O.sub.3]TiC and smooth glass spherical sliders with a radius of 1 mm, and magnetic disks with four different lubricant film thicknesses of 0, 1, 2, and 3 nm. We found that the [Al.sub.2][O.sub.3]TiC slider shows ordinary approach and rebound processes, whereas the glass slider showed a velocity drop at the end of the rebound process when the lubricant thickness was 1, 2, and 3 nm. We identified the elastic force factors in the approach and rebound processes, based on Herztian contact theory, and the damping force factors based on a damping force model that is proportional to slider velocity and penetration depth (contact area). From the drop in velocity when the slider and disk separated, we found that the dynamic adhesion force is almost equal to the static pull-off force except for with a 3 nm lubricant thickness. The dynamic adhesion force with a 3 nm lubricant thickness is significantly higher, probably because of squeeze damping effect. [DOI: 10.1115/1.1843831] Keywords: Head to Disk Interface, Adhesion Force, Elastic Force, Damping Force, Experimental Identification

In this paper, we investigate the effect of lube textures from the viewpoint of lubricant spreading. Lube textures, designating a patterned distribution of bonding strength between lubricant molecules and disk surface, were formed by irradiating ultraviolet rays through a stripe-patterned mask onto a magnetic disk surface which was partially coated with one-monolayer film of perfluoropolyether. Surface characteristics of the lube textures were evaluated by surface energies ascertained from contact angle measurements. Spreading of the lubricant film was measured by scanning microellipsometry on the striped lube textures in the directions parallel and perpendicular to the stripes. The thickness-dependent diffusion coefficients extracted from the spreading profiles show that lubricant spreading in the regime of film thickness less than 0.2 nm is faster along the stripes, indicating the possibility of controlling the behavior of lubricant films with lube textures.

The distribution of the magnetic field and temperature in a superconducting-disk magnetized by pulse field, and the levitation force between the disk and a permanent magnet are calculated. The calculation is based on the current motion and the heat difussion equations.

We have developed a readback equalizer for a perpendicular magnetic disk with a commercial anisotropic magnetoresistive head for use with a PR4ML read channel with 8-9 coding. The transfer function of the perpendicular magnetic disk, derived by Fourier analysis, has a phase lag of 90[degrees] from that of the longitudinal magnetic disk. We defined the parameters of the equalizer by simulation. The equalized readback signal nearly satisfied Nyquist's first criterion. Using resistor-capacitor circuits that correspond to the simulated function, we obtained a byte-error rate of below [10.sup.-7] Comparing the effect of incorporating PR4 or PR1 as part of the equalizer, we observed that PR4 gave a lower bit-error rate than PR1. Thus, PR4 is an effective detection method for a perpendicular magnetic disk. It is suitable not only for longitudinal magnetic disks, but also for perpendicular magnetic disks. Index Terms--Byte-error rate (BER), 8-9 coding, equalizer, Fourier analysis, magnetoresistive (MR) head, perpendicular magnetic disk, phase, PR4ML, pseudodifferential circuit, RC circuit.

The authors describe a technique for using magnetic storage media such as telephone calling cards and floppy disks to demonstrate how information is stored on them. The Bitter-colloid technique, which uses an emulsion of magnetic particles or a magnetic powder to study the bit pattern in magnetic materials, is discussed.

The behavior of a thin lubricant film under a flying head has been studied by examining the lubricant redistribution on the disk after flying, using an HDI-SRA instrument. Lubricant depletion tracks were observed on the disk surfaces and, more interestingly, the lubricant film was found to exhibit a periodic thickness modulation in the downtrack direction. The wavelength of the lubricant thickness modulation is found to increase linearly with the disk linear velocity, and depends weakly on the lube type and lube bonding ratio. The amplitude of the modulation grows slowly with flying time. Both negative-pressure air bearing pico sliders and catamaran-style positive-pressure nano sliders generate similar patterns on lubricant films. The frequency of the thickness modulation is in the range of 40-50 kHz, and is attributed to interactions of the disk lubricant with the slider roll mode. In addition, for highly-bonded lubricant films, a much finer lubricant modulation pattern can be seen with a frequency of 196 kHz, which is very close to the frequency of the pitch mode of the slider. These results indicate that the lubricant thickness modulations on the disk are generated by slider-disk dynamic interactions, and are due to slider body motions. Index Terms--Flyability, head-disk interaction, lubricant, slider air bearing, waviness.

The effect of morphology on flying height modulation (FHM) of a sub-10-nm flying air bearing slider was studied for three different disks by experiment and simulation. The experimental measurement methods are discussed and a new single beam laser Doppler vibrometer (LDV) measurement method, which yielded the highest resolution with a 2 [micro]m beam spot size, was introduced. Analysis was performed in three different frequency bandwidths--a geometric FHM from 10 to 100 kHz, a dynamically excited FHM from 100 to 500 kHz and the third being negligible compared to the other two bands, above 500 kHz. Transfer function analysis was carried out to investigate the FHM in the lowest frequency band. FHM in the first band was shown to be caused primarily by a phase shift between the sliders' response and the disks' morphology and secondarily by decreasing slider motion with decreasing morphology wavelength, which correlated well with previous work. For two of the disks investigated, the FHM due to the disks' morphology showed air bearing excitation that resulted in an intolerable level of FHM. However, for one of the disks studied, the FHM was as low as the disk morphology for wavelengths of 2 mm and less, which was within tolerable limits. It is concluded that when designing a disk for low FHM, it is not sufficient to characterize the quality of a disk by a single number such as roughness or waviness. Proper design and optimization of both the disk and air bearing slider results in FHM that is lower than the disks' morphology. Index Terms--Head-disk interface, LDV, tribology, vibrations.

This study is a computational analysis of the bouncing vibration of a point contact slider model over computer generated random disk surfaces and the design conditions of slider to disk interface parameters necessary for contact recording. The Gaussian random surface of a disk with various standard deviations and frequency characteristics is generated by using a modified midpoint displacement algorithm. From the calculated results of bouncing vibration of a slider for various parameter values, it was found that the decrease in contact stiffness and increase in slider load can significantly reduce the bouncing vibration as well as the increase in contact damping and the smoothness of the surface. It was also found that the bouncing vibration spectrum of a contact slider over a simulated disk surface agreed closely with the experimental results presented in a previous study by the authors. The maximum and rms values of the spacing and the contact force were examined for various design parameters. The design conditions of the contact pad to the disk interface were discussed in terms of tracking ability and wear durability for slider loads of 0.5 mN and 5 mN.

The increasing effort to use sub-ambient pressure air bearing sliders for dynamic load/unload applications in magnetic hard disk drives requires desirable air bearing characteristics during the dynamic unload event. This paper establishes air bearing design criteria for achieving a smooth head unload performance, through a correlation study between the modeled unloading air bearing dynamics of two 30 percent proximity recording sub-ambient pressure sliders and motion sequence of the same sliders by a high-speed video camera. It is shown that the air bearing lifting force quickly responds to changes in fly height and pitch, while the suction force is relatively resistant to changes in fly height, but somewhat more sensitive to changes in pitch. This unique distinction results in different decreasing rates between the air bearing lifting and suction forces during the unload process, creating a strong dependence of the unloading characteristics on the location of the suction cavities. Both the modeled unloading air bearing dynamics and experimentally recorded motion sequence illustrate that a toward-trailing-edge located suction force acts to pitch the slider up, while the moment produced by a toward-leading-edge located suction force induces a negative pitch motion, resulting in an excessive flexure deformation and dimple separation. Therefore, placing the suction cavities towards the trailing edge offers a reliable unloading performance for the sub-ambient pressure air bearing sliders.

The revival of dynamic load/unload (L/UL) technology forces us to rethink the air bearing design philosophy, which has traditionally been established for contact start/stop applications. Reliably loading a slider onto a full-rotating disk imposes its own requirements on the slider air bearing designs. This paper addresses the unique design requirements of dynamic L/UL technology, through an investigation of the air bearing characteristics of two proximity recording sliders during a dynamic load process. While the slider/disk contact force is employed as a key indicator of the reliability of the dynamic load mechanism, the air bearing suction force and squeeze flow effect are used to characterize the slider's dynamics during loading. The effects of the slider's loading velocity, pitch and roll static attitudes on its dynamic load performance are simulated. In comparison to the positive pressure air bearings, both the enlarged air bearing surface and shallowly recessed cavities of the subambient pressure air bearing sliders generate more squeeze flow, resulting in a rapid development of the air bearing lifting force at a higher attitude. This often leads to a more reliable dynamic load performance. The impact of the air bearing suction force on the slider's dynamics during loading is determined by the suction force center. A towards-leading-edge suction force not only induces a negative pitch motion during the early stage, but also prolongs the pitch-up process. Both effects can result in a head crash for the slider with a large negative pitch static attitude. In summary, the subambient pressure air bearing sliders that feature the enlarged leading air bearing surface and towards-trailing-edge suction cavities with small recess depth offer a fast pitch-up load performance.

Conventional sliders were shown to see a stiction barrier at about 0.85 micro inches landing-zone glide avalanche height. In contrast, padded sliders can effectively lower the stiction barrier down to below 0.6 micro inches landing-zone glide avalanche. These indicated that a certain amount of light texture on the disk helped enhance the padded slider head-disk interface durability. It was concluded that the head-disk interface consisting of a padded slider on a light LZT can better meet tribology requirements for high density recording.

This paper presents a microfabricated actuator designed for high precision servo-positioning in a magnetic hard disk drive. The device is actuated using electrostatic force generated with parallel-plate capacitive electrodes. The displacement of these electrodes is measured using a dedicated capacitive sensing interface, allowing closed-loop control to be used to extend the servo bandwidth. Using the sensing electronics and a simple phase-lead compensator, a prototype device was used to actuate a 1.6 mg ceramic slider over a 1.2 kHz bandwidth. Using optical position measurements, the same actuator was used to achieve a 2.5 kHz bandwidth. Index Terms - Actuator, disk drive, micro-electromechanical systems, position control.

We developed a novel piezoelectric microactuator for dual-stage actuator systems in magnetic disk drives. This microactuator is based on the shear deformation of piezoelectric elements, and drives the head suspension assembly. The actuator is suitable for thin devices, and is easily manufactured because of its simple stack configuration. We installed the microactuator in a 2.5[inches] prototype drive, and evaluated the servo system of the dual-stage actuator. This paper describes the structure of our piezoelectric actuator, its mechanical characteristics, and the evaluation of the dual-stage actuator servo system. Index Terms - Dual-stage actuator, magnetic disk drives, microactuator, piezoelectric actuator, shear mode.

Magnetic head - disk interfaces (HDI) which are designed so that the mechanical spacing, between the magnetic recording head and spinning disk media, is so small that frequent intermittent contacts occur during normal steady state operation, can be said to be operating in the 'proximity' recording regime. Mechanical spacing ('fly height') modulation, with characteristic frequency well above the estimated air bearing resonance frequencies, but well below slider ringing frequencies, has been observed in the proximity recording regime. In this paper, the effect of slider preload change, and the effect of atmospheric pressure change, on the frequency and amplitude of such fly height modulation, as measured using laser Doppler vibrometry, is reported. A simple analytical model was developed to explain the existence of the modulation and its observed dependence on applied gram load. Index Terms - air bearing, proximity, near contact, head disk interface.

Certain head/slider movements, such as seeking and dynamic load/unload, may lead to head-disk contact/impact. Such head-disk contact/impact is playing more and more important role in the disk drive failure. As a result, new methodology for the in-situ monitoring of the head-disk interaction and the head-disk spacing change caused by such operations is becoming of crucial importance to the disk drive design and manufacturing. By applying a properly selected DC carrier erasure current on the writing head, the spacing variation during such operations can be recorded and tested. The carrier current is selected in such a way that the spacing change will result in a proportional modulation of the head field acting on the media and lead to a proportional modulation of the magnetization difference between adjacent bit cells. The theoretical background of the method, its working principles and major advantages are discussed. The method is of a unique advantage of getting spacing change recorded. The method is also of the advantage of high sensitivity to the variation of head-disk spacing, comparing with other methods reported with read/write head as transducer. Index Terms - carrier current erasure, head-disk spacing, dynamic load/unload, track seeking, read/write head, magnetic disk drive

Fine particles of aluminum, stainless steel, silicon, slider ceramic ([Al.sub.2][O.sub.3]-TiC) and sputtered alumina were introduced at the head/disc interface of hard disc drives. Experiments were conducted with discs made from aluminum and glass substrates. Glass substrates were much harder than aluminum substrates. It was found that the type of damage introduced on the disc and slider was to some extent unique for each material, and also closely related to the relative hardness of the interacting materials. The introduced particles could be deformed, embedded, disintegrated or sheared. Typical damages on disc caused by particle interaction varied from light deformation to very deep circumferential scratches. From of AFM, SEM/EDX and materials hardness/elastic modulus data, we proposed mechanisms by which particles of different materials could cause damages on the two types of discs.

Characterization of the head and disk surfaces at nanometer dimensions is crucial for optimizing the tribological performance of the head-disk interface as discussed in the following examples given in this paper. Friction mapping at a nano-scale is used to study the nucleation sites of smears on a disk from a failed drive showing high nonrecoverable error rate at the OD. Nanoindentation data suggest that the hardness of the alumina grains is comparable to that of the TiC grains. [Al.sub.2][O.sub.3]-TiC substrates from vendor B exhibit the lowest hardness of 30 GPa. During the CSS test, sliders with vendor B [Al.sub.2][O.sub.3]-TiC substrates exhibit relatively greater amount of wear debris and grain pullouts as compared to those of the vendors A and C. The nature of the damage to the DLC coating during nanoscratching can be qualitatively correlated to hardness, toughness, high residual stresses, and weak adhesion due to an impurity at the coating-substrate interface. The correlation between the highest nanowear resistance and best CSS wear performance of DLC coatings indicates that the wear properties at a nanoscale can be used as an indirect measure of the CSS performance of the carbon overcoats. Index Terms - Head-disk interface, friction mapping, nanoindentation, nanowear, CSS performance.

To investigate the role of disk surface waviness on the baseline instability (BLI) of the read-back signals from MR head, we measured the average height of surface waviness with a spatial wavelength of 0.4 to 5.0 mm using a white light interferometer instrument. We used an MR head over four sets of media to measure the baseline instability at OD and at MD. The results show that the baseline instability becomes worse as the surface waviness increases and that the baseline instability is linearly proportional to the surface waviness. The result further shows that the effect of bias current on the baseline instability is amplified on the disk with worse surface waviness. The surface waviness, therefore, can not be overlooked when evaluating the media for a high-performance hard disk drive. Index Terms - Baseline instability, Magnetoresitive head, Surface waviness, Surface waviness map, Surface waviness measurement

We have demonstrated magnetic recording at an areal density of 5 Gb/[in.sup.2] using Dual Stripe Magnetoresistive heads (DSMR) on low noise and low-glide height quaternary CoCrTa-based alloy thin film disks. The data rate is 120 Mb/sec with a PR4 channel, and the on-track error rate achieved is around [10.sup.-9]. The demonstration was accomplished in two cases using two different types of heads. In the first case, it was done with a DSMR head having shield-shield spacing of 0.165 [[micro]meter] and 1 [[micro]meter] stripe height flying at 25 nm, resulting in a linear density of 321.7 KBPI, and a track density of 15.6 KTPI. The second case was performed with DSMR heads having shield-shield spacing of 0.18 [[micro]meter] and .8 [[micro]meter] stripe height flying at proximity height of 12 nm, achieving a 358.75 KBPI and 13.8 KTPI. This is the highest linear density published so far for either GMR or AMR heads. It is the direct Consequence of high signal/noise of DSMR heads and proximity recording over low noise, low-glide-height media. To explore the large dynamic range of DSMR heads, this study was also done with a variety of low noise disks with Mrt ranging broadly from 0.45 to 1.0 memu/[cm.sup.2] and coercivity of 3000 Oe. Index Terms - DSMR, Proximity recording, Low Noise disks, Stitched Write heads

In this paper, the performance of CoNiO, NiO, NiMn and IrMn as exchange biasing materials for use in spin-valve read heads is described. The significant material properties investigated were biasing fields, thermal stability, thickness effects and corrosion resistance. The oxide materials had excellent corrosion resistance, but NiO had poor exchange fields and CoNiO had a poor blocking temperature. NiMn had the best exchange field with an interfacial exchange coupling of 0.25 erg/[cm.sup.2], but it required high temperature annealing in order to realize this. It also had good thermal and corrosion resistance properties. The blocking temperature of the oxides and IrMn were found to diminish with decreasing thicknesses of the antiferromagnets. This effect was determined to be consistent with a finite-size-scaling phenomenon. IrMn was found to have a good combination of the properties investigated, the weakest being its corrosion resistance, which was nevertheless better than FeMn. Spin-valves fabricated with IrMn as the pinning material showed excellent magnetic and thermal properties with MR ratios as high as 10% and good spin-valve responses up to 209 [degrees] C. IrMn pinned spin-valves had very good performance for narrow trackwidth elements, with MR ratios as high as 5% and pinning fields of > 600 Oe for 0.5 [[micro]meter] trackwidth devices.

On-track recording losses associated with transition curvature in a merged magnetoresistive-read/inductive-write recording system were investigated. Variations in write head design resulted in a wide variation of reproduced pulse width. Magnetic force microscope (MFM) observation of written tracks revealed that transition curvature was related to the pulse width variation. The effect of transition curvature is modeled as a separable loss function by convolving a reader cross-track sensitivity function with a cross-track phase delay profile. Curvature loss has a different spectral content than transition broadening, allowing us to separate the two effects by comparing discrete Fourier transforms of isolated pulses. Results of such an analysis agree satisfactorily with MFM measurements. Planarization of mid-shields had minimal impact on the pulse width, but a notched write head design mitigated the effect. Transition curvature must be taken into account during write head design and in decisions regarding relative read and write widths. Index Terms - Transition curvature, magnetic recording theory, loss terms, MFM, planarized mid-shield, notched pole, write head.

Flying stiction, a high static friction force resulting from a magnetic head seeking/flying over a disk surface, has posed a new challenge in magnetic-disk tribology for low flying heights ([approximately] 30 nm or less), as demanded by high recording densities. Two types of magnetic heads were used in this study. A more than 10-fold increase in flying stiction force was observed for the carbon coated heads after a 24 hours of seeking/flying over the disk surface. Using Time of Flight Secondary Ion Mass Spectroscopy and a scanning micro-ellipsometer, we found that the lubricant pick-up during seeking/flying operation was responsible for the observed 10-fold increase of the flying stiction force. A nearly exponential dependence of flying stiction force on lubricant amount picked up on the air bearing surface (ABS) of the magnetic heads was found. For 24 hours of seeking/flying time, the lubricant accumulated on the ABS surfaces can be up to 1.5 nm, comparable to the lubricant thickness on the disk surfaces. The lubricant amount was found quite uniformly distributed over the ABS surface of the head. Wear on the carbon overcoat of the magnetic heads was also measured, and was equivalent to approximately 1 nm carbon loss for a 24-hour seeking/flying period. The wear rate of the carbon overcoat was very fast for short periods of seeking time ([approximately] 2 hours) and slowed down to near-zero as lubricant built up on the ABS surface, indicating that the lubricant on the head protected carbon wear. The wear of carbon overcoat strongly suggests that intermittent physical contacts between the disk surface and head ABS occurred during seeking/flying operations.

The objective of this paper is to demonstrate, from experiments and modeling, how and why molecular orientation of functional end groups of perfluoro-polyether (PFPE) lubricants play an important role in the tribological performance of thin film magnetic disks. These disks typically have an amorphous carbon overcoat upon which a thin lubricant layer is deposited using dip-coating technique. Glancing-angle FTIR (Fourier Transform Infra-Red Spectrometry) is used for measuring molecular orientation of planer functional end groups. A molecular orientation index (MOI) was defined as 1 for randomly oriented functional end groups. The MOI is mathematically derived as 3 (maximum) for lubricant molecules oriented with their functional end groups perpendicular to the surface, and as 0 (minimum) if lubricant molecules oriented with their functional end groups parallel to the surface. The MOI is shown to depend on processing conditions and lubricant film thickness. The tribological performance of the lubricant films was evaluated using drag-mode contact start-stop testing. It was found that wear durability of the lubricant films ([similar to]2 nm) with MOI [similar to]1.5 is a few times better than those with MOI [similar to]0.5 to 1.0. No significant difference in the amount of bonded lubricant film was detected over the range of MOI studied. Nor was there a detectable relationship with hydrophobicity. It was inferred from decreased MOI values due to thermal effects and storage time that a smaller MOI value corresponds to a lower free energy state of the lubricant film. Interestingly, MOI values for bonded lubricant films for Process A are found to be close to 3.0, suggesting that almost all functional end groups in the bonded films are oriented perpendicular to the carbon surface, close to 2.0 for process B, and close to 0 for process C, meaning that almost all functional end groups in the bonded films from process C are oriented parallel to the carbon surface. Relationship between physical/chemical bonding configurations and MOI values are graphically presented in detail based on this relation, a simple model on lubricant film structures for the three processes studied is presented. The model MOI values agree very well with measured MOI values as a function of lubricant thickness for all three processes, and the model also appears to account for the observed tribology performance for the MOI values studied (0.5 [similar to] 1.5).

Research has established that the critical speed of flexible spinning floppy computer disks is up to ten times more than the critical hydrodynamic coupling speed of thin film housing. Critical spin speed is determined by the clamping ratio in the nonlinear model. Linearized free-vibration calculations are given, together with stability prediction analysis.

In order to measure the spacing between an actual magnetic disk and a slider, we developed a flying height sensor based on frustrated total reflection (FTR). When optically measuring the flying height of a slider, the phase shift on reflection at the magnetic disk is a significant problem. In this paper, we describe the theoretical treatment of the problem, introduce the modified effective refractive index method, and measure the effective refractive index of an actual magnetic disk. The flying height on a magnetic disk was also measured using the obtained effective refractive index. The result was compared with flying height measurements measured by the traditional interference method. They agreed with each other, with an error of less than 2.5 nm. Index Terms - Effective refractive index, flying height, frustrated total reflection.

The magnetic transition region in a CoCrTa/Cr hard disk has been studied with high-resolution Foucault-mode Lorentz microscopy. It was found that the amplitude of the zigzag transition increases significantly at the track edges. Imaging results show that the CoCrTa grains behave magnetically in a clustered manner, forming domains of varying sizes at the transition. The dimension of the smallest grain cluster [or the basic magnetic unit (bmu)] has been determined by studying a pair of antiparallel domain contrast images in this medium. Investigations also reveal that each bmu consists of six to eight CoCrTa hcp grains, giving an average bmu unit size of about 80 [+ or -] 12 nm. Furthermore, the magnetic domain images indicate that the mechanical texture induced by polishing does not break up this intergranular coupling. Index Terms - Basic magnetic units, grain size, magnetic domain, media noise, transition region.

With the increase in track density and higher rotation speeds in hard disk drives, effects contributing to track misregistration (TMR) that heretofore have been negligible in the 3.5 inch form factor are now quite significant. One effect is the vibration of the individual disk platters at their natural frequencies. These resonances are driven primarily by internal windage excitation within the head disk assembly (HDA) during operation. This behavior is a characteristic of all 3.5 inch disk drives using 95 x 0.8 mm aluminum disks. The behavior is dominated by the disk material properties and geometry and not by the spindle, enclosure, or structural design. This disk vibration contributes a significant amount of track misregistration (TMR). Alternate disk substrate materials should be investigated as a means for controlling these effects.

Spin-valve heads utilizing antiferromagnetic NiO layers as the pinning layers were investigated. Advantages of using NiO are (1) superior corrosion resistance, (2) relatively high blocking temperature and (3) reduction in the heat generation due to current shunting. Spin-valve films of a structure of NiO / NiFe / Cu/NiFe show large [Delta][Rho]/[Rho] (approximately 4%) and good sensitivity. Thin Co layers inserted between NiFe and Cu improve both [Delta][Rho]/[Rho] and the thermal stability. To explore the feasibility of spin-valves with NiO, unshielded sensors with hard bias structure having longitudinally magentized permanent magnets were fabricated. Irregular response in the transfer curves can be suppressed when the permanent magnet strength [M.sub.r]t is 0.5memu/[cm.sup.2] or more. The linear response region of the spin-valve sensor was optimized by adjusting the thickness of the pinned layers and the sensor height. Finally, by incorporating these results a shielded spin-valve head with a track width of 2.4[[micro]meter], a gap length of 0.3[[micro]meter] and a sensor height of 0.7 [[micro]meter] was fabricated. The response was noise-free and the output obtained with a small sense current of 0.41mA was approximately 1mVp-p, demonstrating a high sensitivity of a spin-valve head utilizing NiO.

The storage capacities and areal densities found in magnetic disk drives are increasing very rapidly. Data is recorded in ever-narrower tracks which must be followed with extreme precision. Also, the advent of portable applications exposes these smaller drives to higher levels of vibration and shock. A description is given of the many factors which contribute to recording track misregistration (TMR) in today's drives. The mechanics of the drive and actuator and the architecture of the servo control system are also described. A projection is made for the TMR sensitivities and control system at an areal density of 10 Gb/[in.sup.2], having roughly 25 000 tracks/in. A two-stage servo may be needed to achieve such track densities. This would comprise a high bandwidth microactuator for rapid position corrections of the recording head, coupled with a conventional actuator. The characteristics of such a microactuator are discussed, and operational examples of fabricated electroplated microactuators, driven electrostatically, are shown. The mechanical behavior of the devices and the some of the factors which would affect their implementation are also described.

The third order structural parameter, essential to determine the effective conductivity of two-component composites and for manipulating the conductivity, is determined by interface methods for composites with dense, complex suspensions. The third order parameter for dilute random suspensions and composites with simple unit cells is determined using statistical methods. Interface methods involve the implementation of a numerical scheme based on multipole technique. The third order structural parameter is found to be between 0.69 to 0.50.

Analog pre-equalization can play an important role in the performance and monolithic implementation of high speed PRML read channels employing detection in the digital domain by reducing the number of quantization levels required in the analog-to-digital converter. The use of the 3-tap raised cosine equalizer as an analog pre-equalizer in a read channel employing digital adaptive equalization is examined. Following this, a parallel filter architecture suitable for implementation of high speed finite-impulse response filters (including the cosine equalizer) in both the analog and digital domain is described. This parallel filter architecture has been used in the analog domain in both a decimation filter and cosine equalizer in a prototype analog-to-digital interface and in the digital domain in a prototype digital adaptive equalizer/Viterbi sequence detector. Both circuits were fabricated in conservative 1.2 [[micro]meter] CMOS technologies and operate with output sampling rates of 100 MHz.

We define and analyze the ACATS declustering scheme for use with the classic Level 5 as well as MDS RAIDs. ACATS provides a paradigm for distributed Sparing and checking as well. Using Markov models we calculate the reliability of classic Level 5 as well as MDS RAIDs both with and without ACATS. Our results demonstrate, for fixed hardware configurations, trade-offs between performance and reliability within these RAID organizations. Our analysis assumes a transaction oriented environment.

This paper presents a new theoretical approach to the dynamic contact behavior and tracking characteristics of a contact slider that is one of the candidates of head design for future high density magnetic recording disk storages. A slider and its suspension are modeled as a single-degree-of-freedom vibration system. The disk surface is assumed to have a harmonic wavy roughness with linear contact stiffness and damping. From the computer simulation of the time history of the slider motion after dropping from the initial height of 10 nm, it is found that the contact vibration of the slider can attenuate and finally track on the wavy disk surface in a low waviness frequency range. As the wariness frequency increases, however, the slider cannot stay on the disk surface and comes to exhibit a variety of contact vibrations, such as sub- and super-harmonic resonance responses and finally comes to exhibit non-periodic vibration. It is also found that, among design parameters, the slider load to mass ratio and contact damping can greatly increase the surface waviness frequency and amplitude for which the stable tracking of a contact slider is possible.

The transient response of an I-beam friction measurement system to a constant disk acceleration is theoretically analyzed. The friction measurement system is modeled as a single-degree-of-freedom system. It is found that the true breakaway friction is different from the measured breakaway friction, and that the true breakaway time is also different from the measured breakaway time. The system measurement error is evaluated as a function of the acceleration, the effective mass, the spring stiffness, as well as the static and kinetic coefficients of friction. A closed-form dimensionless solution is derived for the system measurement error. If the dynamic effect of the measurement system can be neglected by selecting an appropriate effective mass and acceleration, the maximum possible discretization error can be estimated as a dimensionless function of the discretization frequency, the breakaway friction the spring stiffness, and the acceleration.

Oxidizing catalytic activity of a slider is a factor which could affect wear of magnetic disks with a carbon overcoat. [Al.sub.2][O.sub.3] Composites containing 2-50 mol% [TiO.sub.2] were produced, which had different oxidizing catalytic activities but nearly the same hardness and thermal conductivity. Activation energy (Ec) for carbon oxidation when it is mixed with the composite was measured to get the oxidizing catalytic activity, and it was found that Ec changed from about 70 kJ/mol for [Al.sub.2][O.sub.3] to about 110 kJ/mol for A 1203 containing 9.1-16.7 mol% [TiO.sub.2]. [TiO.sub.2] addition increased and decreased Ec. The former was due to segregation of the Ti-Al-O phase at the,4603 grain boundary, which could inhibit the catalysis at the A/203 grain boundary. The latter was due to the unreacted [TiO.sub.2] phase, which by itself has high catalytic activity. [TiO.sub.2]-[Al.sub.2][O.sub.3] Sliders having different Ec were examined in sliding wear against a magnetic disk with a carbon overcoat using a pin-on-disk test system. It was found that wear rate of the carbon overcoat was lower when the slider had a larger Ec, i.e., lower catalytic activity. It was also found that wear particles of the carbon overcoat were likely to be larger with lower catalytic activity.

[Al.sub.2][O.sub.3]-TiC sliders used in magnetic recording hard disk drives were coated with diamond-like carbon (DLC) to improve the wear durability of the head-disk interface (HDI). Both contact-start-stop and constant speed drag tests were conducted during which the build up of friction associated with wear of the thin film disks was measured in a standard disk wear tester. The friction values increased three or fourfold in the tests with uncoated sliders, whereas tests conducted with DLC coated sliders showed only a twofold increase in friction in the early part of the test followed by constant friction values afterwards. This major improvement was found for as little as 7 nm of coating on the sliders. Increases of wear durability of the head-disk interface by factors of 50-200 were obtained.

Overwrite in thin film rigid disk recording has been studied experimentally using disks with a wide range of magnetic moment and coercivity. Standard f(sub 2)/f(sub 1) overwrite was investigated in detail at various recording currents and different flying heights. A theoretical model was developed using simple analytical approximations that relate demagnetization-field-induced position shift (hard transition shift) to the measured overwrite. The demagnetization fields due to the leading edge transitions were calculated analytically including a good approximation to the gapped head image. The results compare well with experimental measurements. A new overwrite measurement technique using the second harmonic component of a 0.5 f(sub 1) signal is also described in this work.

The current trend in the magnetic storage industry is the reduction of the slider size and the height at which the slider flies over a rigid disk. Lower flying heights are achieved by miniaturizing sliders and reducing the normal load. In this paper, force scaling criteria are determined for 3370 and 3370K sliders that are dynamically loaded or operated in contact start/stop mode. Two forms of the generalized Reynolds equation (the first-order and continued fraction formulations) are incorporated into the analysis. The new scaling equation relates the steady-state flying height to design and operating parameters such as the disk velocity, normal load, ambient pressure, and the shape and dimension of the slider rail. The resulting quadratic equation contains two slider design dependent parameters which are calculated from two full scale numerical solutions to the generalized Reynolds equation for the slider design of interest. The new scaling equation accurately fits numerical and experimental results over an extremely wide range of ambient pressures, normal loads, disk velocities, and slider size reduction. The utility of the scaling equation is that it can rapidly and accurately predict the load required to obtain a desired flying height at a given disk velocity for any slider geometry. The scaling analysis also has the ability to qualitatively account for surface roughness effects. The equation could be applied to the design of contact recording devices, if surface roughness effects could be quantitatively incorporated into the analysis.

Wear characteristics are described for carbon-coated magnetic rigid disks with well-defined surface textures. Concentric circular hills with uniform height (ca. 80 nm) are produced on a disk surface using a photo-lithography technique, to control the apparent area of contact with a slider. Wear depth on the order of nanometers of the carbon overcoat is evaluated from the decrease in hill height after a drag test. Wear depth increases proportionally with the increase in average contact pressure, which is calculated from the load and apparent area of contact between the disk and slider. Lubricant diminishes wear of the carbon overcoat approximately 50 percent compared with that of an unlubricated overcoat.

In this paper, we have shown that a perfluoropolyether lubricant after far-UV irradiation treatment proposed by Saperstein and Lin (1990) was strongly bonded to disk surfaces without depletion from disks rotating at 6000 rpm in a 50 degrees C temperature environment. Nonbonded lubricant (mobile lubricant) on disk surfaces or on the top of the UV-fixed lubricant was easily depleted from rotating disks. Depletion data of the mobile lubricant agreed well with predictions of an inter-slip model. It has been demonstrated experimentally that the mobile lubricant on disk surfaces was simply displaced from the contact or the sliding regions. After a long period of head contact, the lubricant was built up at the head/disk interface due to migration of the mobile lubricant around the contact regions. By contrast, no such build-up was observed for disks with the UV-fixed lubricant. Consequently, long-term stiction was observed for disks with only mobile lubricant, while no stiction was observed for disks with the UV-fixed lubricant. The UV-treated disks also adsorbed less water at high relative humidities compared with the nontreated disks.

Hydrogenated carbon films are being used in the magnetic recording industry as a protective overcoat for the memory disk. In this study, the chemical and surface properties of hydrogenated carbon films were evaluated by using various surface and bulk analytical techniques. These properties were then related to the disks' tribological performance.

Exchange coupling between magnetic multilayers must be controlled for magnetic multilayers to make direct overwriting and super resolution possible in magneto-optical disks. Direct overwriting by light intensity modulation is made possible by using magnetic triple layers with a power margin of plus or minus 30%, a linear density of 0.8 mircrometer/bit and a track pitch of 1.4 micrometer. Super resolution by using magnetic quadri layers enables a linear density of 0.3 micrometer/bit, which is more than three times higher than the density for current MO disks.

A thermal analysis has been used to Predict transient temperature rises at a typical head-particulate-disk interface and a head-thin-film-disk interface. Thermal properties of the various thin-films used in the construction of magnetic rigid disks are measured. Average and maximum transient temperature rises for the assumed head-particulate-disk interface over the contact area are 34 and 44 [degrees] C, respectively for an [Al.sub.2][O.sub.3]-TiC Slider. If the exposed magnetic particles or alumina particles contact the slider surface, the transient temperature rise could be more than 1000 [degrees[ C Average and maximum transient temperature rises for the assumed head-thin-film-disk interface over the contact area are 56 and 81 [degrees] C, respectively for an [Al.sub.2][O.sub.3]-TiC slider and 77 and 100 [degrees] C, respectively for an Mn-Zn ferrite slider. The durations of asperity contact generally are less than 100 ns. The thermal gradients perpendicular to the sliding surfaces are very large (a temperature drop of 90 percent in a depth of typically less than a contact diameter or less than a micron).

Scanning Electron Microscopy and optical profilometer studies were conducted to study the wear of unlubricated thin-film magnetic recording disks overcoated with carbon as well as silver and zirconia. The results indicate that wear of the carbon overcoat occurs in the form of localized damage, or 'pits,' accompanied by a gradual 'thinning' of the carbon overcoat in the wear track. A similar pitting behavior is found for zirconia overcoated disks, but the pits resemble cracks in the overcoat, while the wear of silver disks resembles that of typical metal-metal sliding interfaces., Failures of the magnetic head-disk interface are prevented by applying overcoats on these disks. The wear behaviors of carbon, zirconia and silver-alloy overcoats are studied using Scanning Electron Microscopy (SEM) and optical profilometry. Results show that for carbon and zirconia overcoated disks, damage in the wear track were in the form of small 'pits' or holes, although there is less degree of pitting for zirconia overcoats. Silver-alloy overcoats show large numbers of debris in the form of thin circular flakes on the wear track.