Background of the Invention The present invention relates to surface treatments of magnetic data storage media, and more particularly to the texturing and work hardening of dedicated transducing head contact zones of such media.

In disc drives that support transducing heads aerodynamically during normal operation, surfaces of the discs are formed to provide two separate zones: a data storage zone and a dedicated landing zone or contact zone. The data storage zone is specular and smooth, to minimize the flying height of the aerodynamically supported transducing head. The contact zone is formed with higher roughness, to reduce friction and stiction.

Initially, both zones were mechanically textured, i. e. with abrasives or slurries. More recently, laser texturing of contact zones was found to reduce friction and improve wear characteristics as compared to mechanical texturing. Laser texturing typically involves focusing a laser beam on to a disc substrate surface at multiple locations, forming at each location a depression surrounded by a raised rim as disclosed in U. S. Patent No. 5,062,021 (Ranjan) and U. S. Patent No. 5,108,781 (Ranjan). An alternative approach, disclosed in International Publication No. WO 97/07931 and No. WO 97/43079, is to form domes or nodules. In either event, multiple texturing features cooperate to provide a controlled texture pattern throughout the dedicated contact zone.

Despite the considerable success of laser textured media, certain difficulties have been recognized as demands for increased data storage densities have led to further reductions in transducing head flying heights.

One of the difficulties arises due to the nature of the laser-formed nodules. Although their heights have been reduced, there is less than a corresponding or proportional reduction in nodule diameter. As a result, a transducing head slider at rest on the shortened nodules, at least slightly elastically deforming the nodules, contacts the nodules over an increased total contact area. The result is a diminished capacity to counteract stiction.

A closely related problem is the wear and debris caused by take-offs and landings of the head slider.

Aside from increasing data storage density, efforts to maximize data storage capacity include attempts to use the entire data storage zone including the portion bordering the dedicated contact zone, typically the most radially inward data tracks. When reading or recording data along such tracks, the transducing head is positioned with its inner rail over the laser bumps of the contact zone. The bumps can cause unwanted turbulence in the air bearing, negatively affecting the stability of the slider. Further, there is a risk of catastrophic failure due to interference between the slider and the laser nodules.

Accordingly, it is an object of the present invention to provide an alternative approach to laser texturing that affords the advantages of laser texturing while permitting substantially reduced transducer flying heights throughout a data storage zone, including portions adjacent the dedicated contact zone.

Another object is to provide a process for fabricating data storage media with increased resistance to wear and reduced tendencies to generate debris from head/disc contact along the contact zone.

A further object is to provide a magnetic data storage medium in which the dedicated contact zone has a reduced profile, in terms of extension outwardly beyond a nominal surface plane of the disc.

Yet another object is to provide a less costly, more efficient process for fabricating magnetic date storage media.

Summarv of the Invention To achieve these and other objects, there is provided a process for treating a magnetic data storage medium, including: a. providing a substrate formed of a non-magnetizable material and having a substrate surface suited for supporting an overlying magnetizable film; and b. peening the substrate surface at least over a selected region thereof, to controllably alter the topography of the substrate surface along the selected region and to induce surface-level residual compressive stresses over the selected region.

Preferably, the peening step comprises directing multiple projectiles toward and against the substrate surface along the selected region, which causes multiple local plastic deformations of the non-magnetizable material. Also, it is preferred to use projectiles that are substantially uniform in size, shape, and composition. A variety of materials can be employed, including balls of steel or another metal, ceramic or glass beads, and even organic materials such as walnut shell fragments. One highly preferred material is sodium bicarbonate (NaHCO3), a water soluble salt with abrasive qualities, with the projectiles taking the form of crystals or crystalline particles. The beads, balls or fragments preferably have diameters, or equivalent cross-sectional dimensions in the case of irregular or non-spherical particles, in the range of 1-25 microns.

Spherical projectiles form substantially spherical depressions in the substrate upon impact. Non-spherical particles form irregular depressions, e. g., crevices in the substrate material. In either event, the impact of the projectile causes a highly localized plastic deformation, essentially a stretching of the material along the substrate surface. Surface deformation is resisted by material beneath the surface, creating residual compressive stresses along and near the surface, and counterbalancing tensile stresses deeper within the substrate material. Cold worked in this manner, the substrate surface exhibits improved resistance to cracking or other damage that might occur due to contact with a transducing head slider.

More generally, the plastic deformation toughens the surface by increasing its resistance to further plastic deformation.

The peening process advantageously employs projectiles at a density sufficient to ensure that neighboring depressions overlap one another. This better ensures work hardening throughout the selected region, or over the entire substrate surface, as desired. Also, the overlapping results in a highly desired profile for the texturing, in which the peak regions (the most outward regions, or maximum height regions of a horizontal substrate surface) provide narrow line or point contact with a slider at rest on the contact zone. Thus, the peened texturing results in a smaller contact area over which the slider and disc are contiguous, to more effectively counteract stiction, while still allowing densely arranged, even overlapping features.

Another advantage of the peened profile is that substantially all of the desired increase in surface roughness is due to the inwardly directed depressions, rather than outwardly projecting nodules or rims as in laser texturing. This reduces the turbulence in the aerodynamic bearing supporting a head slider over the data zone and adjacent the dedicated contact zone, and also reduces the risk of interference between the slider and the contact zone surface.

Peening with projectiles, frequently called shot peening or ball peening, can be accomplished using a nozzle that directs a serial stream of spheres or other projectiles toward and against the selected region of the substrate surface. Texturing is limited to the selected region by a controlled movement of the substrate and nozzle relative to one another. For example, a disc-shaped substrate can be rotated, and either simultaneously moved or stepped in the radial direction. Alternatively, the nozzle can be stepped or moved radially. The result is a precisely defined annular contact zone.

In an alternative approach, a much broader stream or spray can be directed toward the disc, whereby multiple projectiles reach the substrate surface simultaneously. With this approach, it is advantageous to mask all areas of the substrate surface except the head contact zone or any other portion intended for peening. This latter,"shot gun"approach considerably reduces the time needed for texturing, as compared to peening using a serial projectile stream, and has the potential for considerable reduction in fabrication costs, despite the additional masking step.

As noted above, the projectiles can be provided in a variety of sizes, shapes, and compositions. Further, parameters of the peening stage can be selected to achieve desired textures. Such parameters include the velocity of the projectile stream, the frequency (projectiles per unit time), and the duration of peening. The peening process can occur in several stages employing different projectiles, e. g., a smaller sized sphere followed by a larger sized sphere to blunt certain peak regions, or a stage employing non-circular or even acicular projectiles followed by a stage employing beads or balls. Alternatively, mixtures of different types of projectiles can be applied in a single stage.

Further, a peening stage can be used in conjunction with other texturing methods. For example, a peening stage can be used after a mechanical abrasion, to work harden the surface, smooth the surface by removing jagged peaks and other acicular features, and increase surface roughness by enlarging the differential between the outward peaks and the inward extent of the depressions.

According to another aspect of the invention, there is provided a non-magnetizable substrate for supporting a layer of magnetizable material capable of storing magnetically readable data. The substrate is formed of a non-magnetizable material and has a substantially planar substrate surface. At least a selected region of the substrate surface is characterized by multiple depressions extending into the substrate inwardly of a nominal surface plane of the substrate surface. The surface further is characterized by residual surface-level compressive stresses at least over the selected region. In a preferred embodiment, the non-magnetizable material includes aluminum, and further includes a nickel-phosphorous alloy that forms an alloy layer on the aluminum at a uniform thickness. In this case, the substrate surface is an exposed surface of the nickel-phosphorous layer.

Yet another aspect of the present invention is a magnetic data storage medium. The storage medium includes a substrate formed of a non-magnetizable material and a magnetizable film deposited over the substrate. The storage medium has a storage medium surface including a contact region adapted for surface engagement with a magnetic data transducing head during accelerations and decelerations of the storage medium with respect to the transducing head. The storage medium surface further includes a data storage region.

Multiple depressions are formed in the contact region, by multiple local plastic deformations of the substrate followed by depositions of the magnetizable film at a substantially uniform thickness whereby the magnetizable film tends to replicate the topography of the substrate supporting it. The depressions cooperate to define a surface roughness of the contact region.

A magnetic data reading and recording apparatus, constructed according to the invention, includes the storage medium and further includes a magnetic data transducer, and means for supporting the transducer in a selected orientation relative to the data storage medium. The transducer further is supported for a controlled movement relative to the recording medium to facilitate selected positioning of the transducer relative to the storage medium in proximate, spaced apart relation to the storage medium surface.

Thus in accordance with the present invention, a data storage medium, at least over a selected region of its surface, is textured in a manner that work hardens the textured material, enhances surface roughness primarily due to inwardly extending depressions rather than outwardly extending peaks, and reduces stiction by minimizing the areas of peak regions of the texture contiguous with a transducing head slider at rest on the storage medium. The arrangement allows closer flying heights, and further allows complete use of data storage zones including portions of the zones adjacent dedicated contact zones while maintaining the stability of the aerodynamically supported slider. Further, peening with wide streams of multiple projectiles can significantly reduce the time needed for texturing, and thus reduce the cost of media fabrication.

In the Drawings For a further understanding of the above features and advantages, reference is made to the following detailed description and to the drawings, in which: Figure 1 is a plan view of a magnetic data storage disc having a dedicated contact zone textured in accordance with the present invention, and a data transducing head supported for generally radial movement relative to the disc; Figure 2 is an enlarged partial sectional view of the data storage disc in Figure 1; Figure 3 is a partial surface profile of a magnetic media substrate with a laser textured contact zone; Figure 4 is a partial surface profile of the data storage disc shown in Figures 1 and 2; Figure 5 is a schematic view of an apparatus for surface texturing a data storage disc substrate in accordance with the present invention; Figure 6 is an enlarged partial view of the profile in Figure 4; Figure 7 is a schematic view of an alternative apparatus for surface texturing in accordance with the present invention; Figure 8 is a schematic view of another alternative texturing apparatus; Figure 9 is a partial profile of an alternative embodiment magnetic data storage medium textured in accordance with the present invention; and Figures 10-12 illustrate further alternative embodiment magnetic data storage media surface profiles.

Detailed Description of the Preferred Embodiments Turning now to the drawings, there is shown in figures 1 and 2 a medium for reading and recording magnetic data, in particular a magnetic disc 16 rotatable about a vertical axis and having a substantially planar horizontal upper surface 18. A rotary actuator (not shown) carries a transducing head support arm 20 in cantilevered fashion. A magnetic data transducing head 22, including a magnetic transducer and an air bearing slider, is mounted to the free end of the support arm, through a suspension 24 which allows gimballing action of the head, i. e. limited vertical travel and limited rotation about pitch and roll axes, A rotary actuator and the support arm pivot to move head 22 in an arcuate path, generally radially with respect to the disc.

At the center of disc 16 is an opening to accommodate a disc drive spindle 26 used to rotate the disc. Between the opening and outer circumferential edge 28 of the disc, upper surface 18 is divided into three annular regions or zones: a radially inward zone 30 used for clamping the disc to the spindle; a dedicated transducing head contact zone 32 (sometimes called a landing zone); and a data storage zone 34 that serves as the area for recording and reading the magnetic data.

When the disc is at rest, or rotating at a speed substantially below its normal operating range, head 22 is in contact with upper surface 18. When the disc rotates at higher speeds, including normal operating range, an air bearing or cushion is formed by air flowing between the head and upper surface 18 in the direction of disc rotation. The air bearing supports the head above the upper surface. Typically the distance between a bottom edge 36 of head 22 and upper surface 18, known as the head"flying height,"is about 1 to 2 micro-inches (25 to 50 nm) or less. Lower flying heights permit the magnetic data to be stored at higher densities.

For data recording and reading operations, rotation of the disc and pivoting of the support arm are controlled in concert to selectively position transducing head 22 near desired locations within data zone 34. When power is turned off, or in some drives following a data operation, the disc is decelerated and support arm 20 is moved radially inward toward contact zone 32. By the time disc decelerates sufficiently to allow head/disc contact, the head is positioned over the contact zone. At power-on or before the next data operation the disc is accelerated, initially with head 22 and contact with the disc within contact zone 32. The support arm is not pivoted until the head is free of the contact zone, i. e. supported by an air bearing.

Magnetic disc 16 is formed by mechanically finishing an aluminum substrate disc 38 to provide a substantially flat upper surface. Typically a nickel-phosphorus alloy has been plated onto the upper surface of the substrate disc, to provide a non-magnetizable layer 40 with a uniform thickness, e. g. in the range of about 2-12 microns. Following plating, an upper substrate surface 42 of the Ni-P alloy layer is polished to a roughness of, e. g. about 2.5 nm or less.

After mechanical finishing, substrate surface 42, at least along the contact zone, is textured to provide a desired surface roughness. As noted above, mechanical abrasion techniques and laser energy have been employed to provide desired surface textures. In accordance with the present invention, and as explained in more detail below, a peening process is used to provide the desired textures.

With further reference to figure 2, fabrication of disc 16 involves the application of several layers after surface texturing of the substrate. The first of these is a chromium underlayer 44, typically having a thickness of about 10-100 nm. Next, a magnetizable material is deposited onto the chromium underlayer, to provide a magnetic thin film recording layer 46 for storing the data. A typical thickness of the recording layer is 10-50 nm, and examples of suitable magnetic materials include cobalt-based alloys such as CoCr, CoCrTa, and CoCrNi. The final layer is a protective carbon layer 48, applied to a thickness of 5- 30 nm. Layers 44,46 and 48 are substantially uniform in thickness, and thus replicate the texture of substrate surface 42, to impart the desired texture to upper surface 18.

The present invention and its advantages are better understood from a perspective that includes some familiarity with using laser energy to control surface textures. Laser texturing involves forming discrete nodules (also called bumps or domes) along the surface of a substrate disc. The shape and size of the nodules depend on the level of laser beam energy and the degree of focus. Typically the nodules are formed in a spiral path, having a circumferential pitch governed by the disc rotational speed and laser pulsing interval during texturing. A radial pitch is imparted by shifting the laser radially, or shifting the disc relative to the laser. The nodules can be formed with a high degree of uniformity in height (distance between the nodule peaks and a nominal surface plane of the disc), to provide a uniform surface roughness throughout the contact zone.

Figure 3 is a schematic surface profile view of a laser textured disc, showing part of an upper substrate surface 50 with a dedicated contact zone 52 and a data storage zone 54.

Several nodules 56 are shown along the contact zone. A transducing head slider 58 is supported above surface 50 by an air bearing. A radially inward rail 60 of the slider is over contact zone 52, while an outer rail 62 of the slider is over the data zone, centering the slider over a point 64 representing the most radially inward data track, i. e. the track adjacent the contact zone. The surface profile in figure 3 corresponds to a radial section through the substrate disc, so that the circumferential direction is perpendicular to the plane of the figure.

From figure 3 it is apparent that nodules 56 limit the flying height of slider 58, in the sense that the flying height must be greater than the height of nodules 56 above the nominal plane of surface 50. Otherwise, inward rail 60 of the slider would crash into the nodules as the slider is moved radially inward from the data zone to the contact zone. Even when the average flying height exceeds the nodule height, there is a substantial risk of slider/nodule contact due to the gimbal mounting of the slider. Further, when the slider is positioned as shown in figure 3, it is subject to turbulence in the air bearing due to nodules 56, increasing the degree of any slider instability and thus increasing the risk of contact with the nodules.

In practice, this problem has been avoided by placing the most radially inward data track sufficiently remote from the contact zone so that the slider, when acting on the inward track, is completely within the data storage zone. Alternatively, a transition zone is formed between the data zone and contact zone, in which nodules are formed with steadily diminishing heights in the radially outward direction. Neither approach addresses the desire to use the complete storage zone for storing data.

Figure 4 is a schematic profile view similar to that in figure 3, but showing surface 18 of disc 16, in particular including parts of data zone 34 and contact zone 32. Contact zone 34 is textured by forming multiple adjacent or overlapping depressions 66. The surface roughness is defined primarily by the depth (typically in the range of 2-8 nm) or inward extension of the depressions, in contrast to contact zone 52 in figure 3 where the peak heights define the surface roughness. The depressions are formed at a high density, with adjacent depressions overlapping one another. As a result, the region of contact zone 32 that directly supports an at-rest slider, through contiguous surface contact with the slider, is comprised of multiple peaks 68. The peaks cooperate to support transducing head 22 when the head is at rest upon the contact zone. Given the peak geometry as seen in Figure 4, i. e., the relatively steep slopes of the peaks, the surface area over which the slider and surface 18 are contiguous is comprised of thin regions on the order of lines or points. Consequently the region of actual contiguous contact is extremely small in proportion to the surface area of the slider bottom edge. This considerably reduces stiction, i. e. the tendency of slider 22 to adhere to the contact zone surface during disc start-up (acceleration).

By contrast, laser-formed nodules 56 are considerably more rounded or blunt, and can be elastically deformed when supporting a slider to enlarge the contiguous surface contact area. Of course, the spacing between neighboring nodules 56 can be increased to reduce the contiguous surface contact area between the slider and the nodules. However, the peened texture of contact zone 34 is unique, in that it provides the combined advantages of adjacent or overlapping features and a substantially reduced contiguous contact area.

Further in contrast to nodules 56, peaks 68 do not protrude substantially above a nominal surface plane of surface 18, although they might be situated slightly above or slightly below such plane as viewed in figure 4. The surface roughness over the contact zone is defined by the vertical distance between the peaks and the bottoms of the depressions, essentially the same as the depth of the depressions into the substrate material below the nominal surface plane. As a result, peaks 68, in contrast to nodules 56, do not impose a limit on the slider flying height, since the peaks are substantially co-planar with the nominal surface plane of the disc. The risk of catastrophic failure due to impact of the slider with raised contact-zone features is virtually eliminated. Although slider 22 when positioned as shown in figure 4 is subject to turbulence in the air bearing beneath an inner rail 70, any resulting slider instability is less likely to cause catastrophic failure.

Thus, radially inward tracks in data zone 34, e. g. as indicated at 72, can be utilized without undue risk, and without the need for a transition zone between the data zone and contact zone.

Figure 5 schematically illustrates an apparatus 74 for treating disc 16 to provide the contact zone texture shown in figure 4. The texturing apparatus includes a stationary nozzle 76, a container 78 filled with glass or ceramic beads, metal balls or other projectiles, and a passageway 80 for conveying the projectiles to the nozzle. A source of pressurized air 82 is coupled to the nozzle through a conduit 84. Individual projectiles 86 enter the air stream and are propelled serially toward disc 16 in a linear path as shown.

The desired texture pattern is formed by rotating disc 16 using a spindle 88, and by radially translating the disc relative to the projectile stream, for example by a motor 90 operating on a shaft 92 to move a non-rotating part of spindle 88 upwardly and downwardly as viewed in the figure. The projectile stream can be caused to trace a spiral path by simultaneously rotating and radially translating disc 16. Alternatively, the disc can be radially stepped between successive rotations to form concentric annular traces. In either event, disc rotational and radial velocities are selected with respect to the rate at which the peening elements exit nozzle 76, to insure the desired overlapping of adjacent depressions.

Alternatively, the disc can be translated at greater speeds and the tracing of the selected surface region can be repeated several times. In either event, given peening elements of uniform size and shape, apparatus 74 can be used to determine, at least on the average, the degree of overlap of adjacent depressions.

Parameters other than disc velocity and peening element frequency can be controlled to selectively alter texture patterns. The peening elements or projectiles themselves can be selected, as to size, shape and composition. Spherical elements produce spherical depressions such as shown in Figure 4. Non-spherical elements with corner, or even acicular features, can be employed to produce ravine or crevice-like features in disc substrates.

The sizes of the depressions are determined in large part by the sizes of the peening elements. Element composition, particularly as it determines hardness, also plays a major role in determining the sizes of the depressions. While it is not essential that the hardness of the peening elements exceed the hardness of the substrate, harder projectiles cause more plastic deformation of the substrate, assuming the same velocity at impact.

The velocity at which nozzle 76 propels the peening elements also can be varied. In general, softer peening elements must be propelled at higher velocities. Finally, the duration of the peening process can be varied to alter the results, particularly the degree of work hardening and the statistical distribution of depressions.

In Figure 6, a portion of Figure 4 is enlarged to illustrate one of depressions 66. The broken line at 94 indicates the nominal plane of surface 42, also the actual plane of the surface prior to impact of the projectile. The projectile forms depression 66 by deforming the substrate material, more particularly by stretching the material near substrate surface 42 to achieve the substantially spherical shape depicted in the figure.

The deformation is plastic. In other words, the material near the surface is stretched beyond its elastic limit. The substrate material also is elastically deformable. Consequently, the elongation of the substrate material at and near the surface is counteracted by material at greater depths within the substrate. The result is a coexistence of forces induced by the peening action: compressive stresses at and near surface 42, conveniently referred to as surface-level compressive stresses; and counterbalancing tensile stresses at a greater depth within the material. Inwardly pointing arrows 96 represent compression, while the outwardly pointing arrows 98 represent tension. A broken line at 100 indicates that the compressive forces are nearer to the surface, and is not intended to represent a line or surface of demarcation between tension and compression.

A salient feature of the present invention is the enhanced surface toughness and resistance to wear imparted by the peening process. The surface-level compressive stresses resist formation and spreading of cracks, so that the substrate is less susceptible to wear or damage from landings, takeoffs, and other incidental contact with sliders, and also more effectively withstands any thermal cycling.

An additional benefit of the peening process is the work hardening that results from plastic deformation of the substrate. In particular, peening improves surface properties because the plastic deformation increases the yield strength of the material that undergoes plastic deformation. Within limits, increases in the amount of plastic deformation produce corresponding increases in the yield strength. Accordingly, the duration of the peening process is a key factor in the degree of surface improvement.

Apparatus 74 can be a commercially available ball peening or shot peening device.

Suitable sodium bicarbonate peening elements, and a variety of other peeing elements, also are commercially available.

Figure 7 schematically illustrates an alternative apparatus 102 for texturing a disc 104.

The apparatus includes a tube 106, a peening element container 108 for supplying peening elements to the tube, and a source 110 for supplying air under pressure to the tube via a conduit 112. Tube 106 is designed to propel peening elements toward the disc in a spray, in which multiple elements strike the substrate surface at any given instant during peening, over a comparatively broad impingement area. This approach is more rapid but less accurate than the linear projectile stream produced by apparatus 74. Accordingly, it is advantageous to apply a mask to areas of the disc surface not intended for texturing, as indicated at 114 in Figure 7. In spite of the need to apply the mask, overall processing time is reduced substantially by the volume of peening elements impaled against the disc, enabling more rapid, lower cost fabrication.

A further alternative texturing apparatus 116, shown in Figure 8, includes a tool 118 having a pin 120 (with a blunt tip 122) that reciprocates within a case 124. A disc 126 can be supported for rotation and radial translation as in Figure 5. Alternatively, the disc can be maintained stationary, with case 124 translated as needed to texture the selected region of the disc surface. In either event, Pin 120 reciprocates in the direction perpendicular to the disc surface. Pin 120, particularly blunt tip 122, has a hardness greater than that of the disc substrate.

Further in accordance with the present invention, the texturing process can employ mixtures of different types of peening elements, or can incorporate several stages involving different sizes, shapes or compositions of the peening elements. For example, Figure 9 illustrates the profile of a substrate surface 128, particularly within a dedicated transducing head contact zone. The profile shown is the result of a two-stage peening process employing beads or other spherical peening elements. During the first stage, a smaller sized element (e. g., five microns in diameter) is used to form depressions 130. During the second stage, larger diameter beads (e. g., 20 micron diameter) are used to smooth the texture somewhat by blunting peaks 132 between adjacent depressions. The larger diameter, second stage peening elements preferably are propelled at a substantially lower velocity than the smaller diameter particles, or alternatively are composed of a substantially softer material.

Figure 10 is a profile of a substrate surface 134, in particular within a contact zone, treated according to a two-stage peening process, in which the larger diameter beads are employed during the first stage, thus to form primary depressions 136 that determine the surface roughness of the contact zone. During the second stage, smaller diameter beads are used to form secondary depressions 138, mainly to accomplish further work hardening of the substrate surface.

Figure 11 illustrates the profile of a substrate surface 140 treated with non-circular peening elements, e. g., particles of sodium bicarbonate or other crystalline materials. Even when such peening elements are provided at a substantially uniform size, the resulting depressions 142 lack the uniformity of depressions produced by spherical elements, with the depth and shape of each depression depending in part on the orientation of the crystalline particle at the point of impact.

In addition, irregular elements such as fragments can be utilized to produce deep, crevice-like or ravine-like depressions useful for retaining liquid lubricant throughout the contact zone. Figure 12 illustrates the profile of a substrate surface 144 including a contact zone 146 and a data zone 148, both of which have been treated by peening. More particularly, data zone 148 has been treated with peening elements in the micron range, primarily to work harden the surface. Texture zone 146 is formed in two stages, including the formation of primary depressions 150 with larger diameter spherical particles, followed by a stage employing substantially smaller crystalline particles or fragments, to further work harden the surface and form lubricant-retaining crevices 152. In lieu of the two stage process, a mixture of the spherical particles and the crystalline fragments could be employed.

Thus in accordance with the present invention, surfaces of nonmagnetic substrates are textured and work hardened simultaneously, resulting in magnetic media with controlled textures that reduce friction and stiction, and exhibit improved hardness and resistance to wear. The desired contact zone texture is achieved by forming inwardly projected depressions rather than outwardly projected nodules, enabling reduced slider flying heights by virtually eliminating the risk of impact of a low flying slider against contact zone features as it is moved radially inward with respect to the disc. Magnetic data can be stored at greater density throughout the data storage zone, including along tracks adjacent to the contact zone, resulting in media with enhanced storage capacities. Mixtures of peening elements, or multiple stage peening, can be employed to form textures with unique, specialized topographies.