The critical conditions (critical stress and critical temperature) for the demagnetization of perpendicular magnetic recording disks were investigated. A tribo-demagnetization test of a perpendicular magnetic recording disk with a low load ball-on-disk system and the scan of the disk with the magnetic head were sequentially carried out to evaluate the critical force and sliding velocity for the occurrence of demagnetization, and the relationship between the two critical factors. Then, a finite element model using thermomechanical coupling was developed to calculate the critical stress and temperature of the magnetic disk based on the critical force and sliding velocity of the experiment result. Finally, a method based on the tribo-demagnetization test in combination with finite element analysis to calculate the critical conditions for the demagnetization of the perpendicular magnetic recording disk under sliding contact was proposed.

Model scratches of the size found in hard disk drives are produced under controlled conditions at a series of applied loads on both longitudinal magnetic recording (LMR) media and perpendicular magnetic recording (PMR) media using a diamond tip. The scratches are created at low speed, eliminating thermal considerations from the interpretation of the media response. Nanoindentations are produced as well. The scratches and indentations are characterized by atomic force microscope (AFM), magnetic force microscope (MFM), and also by the same magnetic reader and writer used in an integrated hard disk drive (HDD). A comparison of the response of PMR and LMR media shows the PMR media to have larger scratches and greater magnetic signal degradation than LMR media for a given scratch load. The extent of magnetic damage, as measured by MFM, is greater than the extent of surface mechanical damage, as measured by AFM. Analysis of scratches using the HDD reveals that the magnetic damage is irreversible and permanent damage in magnetic layer, which is confirmed by cross section transmission electron microscope image. The experiments reveal the mechanism for magnetic scratch erasure in the absence of thermal effects. This understanding is expected to lead to improved designs for mechanical scratch robustness of next-generation PMR media.

A single-degree-of-freedom spring-mass-damper model has been developed to simulate the dynamic response of a typical magnetic recording slider under the effect of intermolecular forces. Thornton and Bogy (2003, IEEE Trans. Magn., 39(5), pp. 2420–2422) have previously reported that the slider “snaps” to the surface of the disk, below a certain “critical” flying height, due to the intermolecular forces. We have studied impulse response of the model to show that the slider can snap even at flying heights greater than the critical flying height and that the occurrance of snapping also depends on the magnitude of the applied impulse.

To achieve the areal density goal in hard disk drives of 1 Tbit ∕ in . 2 the minimum physical spacing or flying height (FH) between the read/write element and disk must be reduced to ∼ 2 nm . A brief review of several FH adjustment schemes is first presented and discussed. Previous research showed that the actuation efficiency (defined as the ratio of the FH reduction to the stroke) was low due to the significant air bearing coupling. In this paper, an air bearing surface design, Slider B, for a FH control slider with a piezoelectric nanoactuator is proposed to achieve virtually 100% efficiency and to increase dynamics stability by minimizing the nanoscale adhesion forces. A numerical study was conducted to investigate both the static and dynamic performances of the Slider B, such as uniformity of gap FH with near-zero roll over the entire disk, ultrahigh roll stiffness and damping, low nanoscale adhesion forces, uniform FH track-seeking motion, dynamic load/unload, and FH modulation. Slider B was found to exhibit an overall enhancement in performance, stability, and reliability in ultrahigh density magnetic recording.

System identification methods have been used to study the response of a magnetic recording slider during contact with a scratch on the disk surface. In addition, the slider response was studied taking into account the effect of disk micro-waviness at various disk rotational speeds. The simulated slider response was compared with the measured slider dynamic behavior. Very good agreement was found between simulated and measured data. The flying height modulation of the slider, due to disk micro-waviness, was found to depend on disk velocity.

A novel technology to smooth the metal tab surfaces using a pulsed laser beam is applied to reduce the wear of the load/unload ramps used in disk drives that employ load/unload technology. The laser pulse length, pulse energy and the pulse repetition rate are so chosen that they cause the surface layer of the load/unload tab, approximately 2–3 um deep, to melt and refreeze quickly. As the surface layer melts, the surface tension of the melt removes most of the micro roughness and a smooth surface is obtained. The reduction in the micro surface roughness is confirmed by the AFM traces and a sharp decrease in the light scattered from the tab surface. In wear tests, such tabs show a remarkable improvement in the wear of the plastic load/unload ramps, allowing 5–10 × more load/unload cycles for a given amount of ramp wear.

The influence of alumina and titanium carbide, components of magnetic recording sliders, on the carbon gasification reaction was investigated. Pure alumina and titanium carbide powders were each combined with graphite powder and subjected to thermogravimetric analysis (TGA). The molar ratio ranged from 0 to 20 mol percent; graphite powder was the balance. From the thermogravimetric analysis, the activation energy E a of the reactions was determined. It was found that the activation energy for carbon gasification reduced slightly for increasing alumina mole percentage. Titanium carbide additions markedly increased the activation energy. This increase indicates a competitive oxidation reaction that forms titanium oxide, as confirmed by X-ray diffraction (XRD). As a result of these observations, titanium oxide was also mixed with graphite powders and analyzed by TGA. Titanium oxide has an activation energy behavior that becomes more complex with increasing mole percentage: the activation energy first increases and then decreases. These data are presented and the oxidation reaction is proposed.

A new method to evaluate the distribution of perfluoropolyether lubricant on hard disks was developed. We used a scanning probe microscope (SPM) technique with the dynamic force mode to detect the adhesion between the tip and the lubricant layer. We found that the distribution of phase of the cantilever oscillation varied with the cantilever amplitude when hard disks were observed, and that the behavior of how the phase image varies with the cantilever amplitude gives the distribution of the lubricant. The relative lubricant amount estimated by this method was linearly correlated with the lubricant thickness measured by Fourier transform infrared spectroscopy (FT-IR). This suggested that the method could quantitatively evaluate the lubricant distribution. Visualization of the lubricant distribution showed that the lubricant was thicker at the bottoms and thinner at the bevels around grooves in the mechanical texture. [S0742-4787(00)02104-4]

This paper describes head/disk interface dynamics for micromachined mother ship negative pressure slider bearings with an integrated microsuspension mechanism that we proposed, at steady-state flying in proximity magnetic recording. The authors first indicated the analytical model for air bearing dynamics of mother ship slider mechanisms, and the advantages of the mechanisms were discussed from the dynamics points of view, compared with conventional flying head slider mechanisms. Dynamic design considerations and optimization for micromachined mother ship negative pressure slider bearings with an integrated microsuspension mechanism were also investigated. Finite element simulation for the stiffness analysis of a microsuspension mechanism was carried out and the design optimization for low stiffness gimbals was studied. Furthermore, the effects of slider mass ratio and slider car film stiffness ratio of a secondary slider to a primary slider on mother shipslider dynamics were analyzed numerically. Considering those numerical simulationresults, system optimization for sliders as well as microsuspension gimbals was established to achieve head/disk interface reliability in high density proximity magnetic recording.

The physical damage at the Head-Disk Interface (HDI), caused by common ceramic particles found in the manufacturing environments of the heads and disks in hard magnetic disk drives, is reported. The need for this study arises from industry wide reliability problems due to particulate induced damage at the HDL The intent of this study is to characterize the head/disk damage caused by 1 μm diamond, 1–2 pm Tie particles, 0.2–1 μm alumina particles, the alumina and TiC grains sintered to make Al-TiC (the slider body), and sputtered alumina. These particles were introduced to the HDI in over thirty disk drives. The drives were then made to perform magnetic recording and retrieval operations for known data sequences, with the resultant reading errors tabulated. After the functional testing, the drives were opened and resulting damage was examined with a number of surface characterization tools. This study confirms that the severity of problems with the read-back signal, caused by particle damage, has an inverse relationship with the magnetic track width. In addition, the harshness of physical damage to the HDI has a positive relationship with particle hardness. Finally, particle shape and size can be contributing factors in damaging the HDL.

Two of the most difficult issues to resolve in current design of head/disk interface in magnetic recording devices are stiction and durability problems. One method of overcoming these problems is by implementing a technology known as load/unload, where the system is designed so that the slider never touches the disk surface. One potential problem with this type of system is slider/disk contact induced disk defects. The objective of this paper is to show that the likelihood of disk scratches caused by head/disk contacts during the load/unload process can be significantly decreased by rounding the edges of the air-bearing surface. Using the resistance method, we observe that head/disk contacts burnish the corners of the slider and thereby decrease exponentially with load/unload cycles. A well burnished slider rarely causes any disk damage thus resulting in an interface with significantly higher reliability. A simple Hertzian contact stress analysis indicates that the contact stress at the head/disk interface can be greatly decreased by increasing the radius of curvature of the air-bearing surface edges.

The ever shortening product cycle for magnetic recording disk drives demands a fast and accurate numerical prediction of the slider’s flying characteristics during the design stage. A computationally efficient multigrid control volume method is developed in this paper for the solution of the very high bearing number and shaped rail air bearing problems. The control volume schemes for discretizing the Reynolds lubrication equation are based on various convection-diffusion formulations, while the solution of the resulting discretization equations is accelerated by an additive correction based multigrid method. A comparison study using the 50 percent tripad and Headway AAB sliders demonstrates a significant improvement in the solver’s performance as compared to the single-grid method.

The friction and wear micromechanisms of amorphous hydrogenated carbon films were investigated experimentally using commercially available thin-film rigid disks with sputtered carbon overcoats and Al 2 O 3 TiC magnetic recording heads. Continuous sliding tests demonstrated the existence of two distinct friction and wear regimes characterized by different dominant micromechanisms. Scanning electron microscopy and Raman spectroscopy revealed that the evolution of friction in the first regime is due to changes of the surface microtopography and the film structure from amorphous carbon to polycrystalline graphite. Atomic force microscopy showed that the topography changes result from asperity nanofracture leading to the gradual removal of carbon material and the generation of ultrafine wear debris. The friction behavior in the second regime is due to various wear processes arising on the carbon film surface. High friction promotes surface micropitting and the formation of significantly deeper and wider texture marks. The erratic fluctuations of the friction force and microplowing of the carbon film at steady state are attributed to the relatively large wear particles generated by micropitting.

Very thin head-tape spacing, combining contact and floating conditions, is investigated for high density magnetic recording. A generalized lubrication equation, based on a linearized Boltzmann equation, is coupled with the tape deformation equation for analysis. Tape-surface roughness is also taken into account in the lubrication equation. The average flow model is adopted to analyzing tape-surface roughness. For very thin spacing conditions, it is found that the spacing based on the linearized Boltzmann equation is smaller than that based on first-order slip flow, and larger than that based on second-order slip flow. It is also found that considering tape-surface roughness reduces the calculated minimum spacing. Analytical results agreed with the experimental ones.

The stiffness and damping coefficients of a slider gas bearing operating under arbitrary Knudsen number are calculated. A perfect gas is used as the lubricant, and its behavior is described by the modified average Reynolds equation proposed by Makino et al. (1993). The effects of molecular mean free-path on the roughness-induced flow factors are included. The effects of the nondimensional film thickness, H s0 , the surface characteristics, (γ 1 , γ 2 ). the inverse Knudsen number, D 0 , the nondimensional frequency, Ω, and the modified bearing number, Λ b , on the dynamic coefficients are discussed in this paper. As expected, the values of dynamic coefficients for various roughness orientations approach the smooth value as the ratio, H s0 , becomes greater and greater, and thus the roughness effect is getting smaller and smaller. The air film of two-sided longitudinal oriented roughness is stiffer than the other two-sided oriented cases. The effect on translational damping coefficients for various two-sided oriented roughnesses is reversed as D 0 greater than some value, and this value is affected significantly by Λ b . Transversely rough stationary case has the lowest critical value of Λ b , at which the negative translational damping appears. The results show that the roughness effect and rarefaction effect on dynamic coefficients are significant, and they cannot be ignored for stability analysis.

Some fundamental characteristics of the subambient pressure air bearing suction force were investigated analytically and numerically. The performance of air bearing suction force is strongly determined by the cavity bearing number, in which the cavity region recess depth is used as the characteristic film thickness. Although the optimal recess depth for maximum, suction force varies for different operation conditions, the optimal cavity bearing number can be found in a wide range of applications. The analytical model was confirmed by a finite element analysis. Examples of different disc velocities, slider dimensions, and ambient pressure effect were presented.

Further increase in magnetic recording density requires a reduction in slider flying height. The current study employs the short-bearing approximation to determine analytically the static equilibrium configuration of a slider supported by a starved liquid bearing that operates between ideally smooth surfaces. The solution incorporates rheological behavior based on previously acquired data. The accuracy of the short-bearing approximation is assessed by determining how well the resulting solution satisfies the Reynolds equation. The analysis suggests a means of designing a slider to achieve head/medium spacings in the neighborhood of 20 nm.

In this paper, an optimization technique is utilized to find an optimum configuration of the taper-flat slider positioned by a rotary actuator for enhanced static air-bearing characteristics. The aim of optimization consists in simultaneously minimizing the variation in flying height from a target value, maximizing the smallest pitch angle, and minimizing the largest roll angle, over the entire magnetic recording band. As the design variables, the leading edge taper angle and rail width of a taper-flat slider, and the skew angle at the inside track are chosen since they seem to be the most influential parameters on air-bearing characteristics. The optimum design variables are automatically obtained by using the augmented Lagrange multiplier method, and the static characteristics of the optimally designed sliders are found to be superior to those of the taper-flat sliders of typical configuration over the entire recording band. Results obtained for three taper-flat slider models are reported, showing the effectiveness of the proposed design scheme.

The bearing area of conventional texture on magnetic recording disk surfaces shows a tendency of increase with a decrease in surface height. This is believed to be a major reason for the increase of head/disk friction with the accumulation of CSS cycles. In view of this, a novel type of texture is developed in this study. This type of texture consists of discrete pillar-shaped asperities, whose height and shape can be optimized to reduce friction build-up and wear depth during CSS operation. It also allows lower asperity height to reduce take-off velocity and glide height. In addition, it is suitable for landing zone texturing. The discrete texture remarkably outperforms mechanical texture during CSS tests.

A gimbal forming modificaton is presented which, when implemented, leads to significant reduction in air bearing surface (ABS) static attitude and flying height variability within head-gimbal assembly (HGA) populations. The modification requires no additional parts or steps in the manufacture of the suspension assembly. An experimental test of the concept is described, along with the procedure on which it is based. The resulting reduction in product variability is obtained without measurement of (or tailoring to) the initial conditions of the constitutive parts of each HGA. A ≈ 50 percent reduction in static attitude variability, and a ≈ 33 percent reduction in flying variability, was experimentally shown to result from the adoption of the Double Dimple design concept, in all flying degrees of freedom.