Magnetic head slider

Figure 12 A magnetic head slider flying over a disk surface (slider located on the position 1.25 in. from the disk center rotating in 7600 rpm) compared with an aircraft flying in 560 mile/h over ground with a close physical spacing.

In many cases of traditional tribology, friction and wear are regarded as the results of surface failure of bulk materials, the solid surface has severe wear loss under high load. Therefore, the mechanical properties of bulk material are important in traditional friction and wear. However, in microscale friction and wear, the applied load on the interactional surface is light and the contact area is also under millimeter or even micrometer scale, such as the slider of the magnetic head whose mass is less than 10 mg and the size is in micrometer scale. Under this situation, the physical and chemical properties of the interactional surface are more important than the mechanical properties of bulk material. Figure 1 shows the general differences between macro and micro scale friction and wear. 

Fig. 4—The number of CF+ at different positions of the slider surface, (a) air bearing surface (ABS) of magnetic head, (b) CF numbers on different positions of ABS.

Partially fluorinated X-IP has been used for a number of years as an additive in the inert lubricant PFPE film on the surface of a magnetic hard disk to enhance start/stop durability of PFPE lubricants [29,30]. Recently it has been used as a vapor lubricated film on the surface of the disks [31 ]. In order to avoid the PFPE being catalyzed to decomposition by the slider material AI2O3 (refer to Section 3.4), XI -P was also examined as a protective film on the surface of the magnetic heads [25,32]. The results of CSS tests indicate that the thermal stability of the lubricant was greatly improved in the presence of X-1P, and the thickness of X-1P film on the slider surface has an important influence on HDD lubrication properties. 

Luo et al. [1,153] used a slurry containing ultra-fine diamond (UFD) powders to polish the surface of HDD sliders. The powders are from 3 nm to 18 nm in diameter and 90 % around 5 nm. They are crystal and sphere-like [154]. The pH value of the slurry is kept in the range from 6.0 to 7.5 in order to avoid the corrosion of read-write heads, especially pole areas. A surface-active agent is added into the slurry to decrease the surface tension of the slurry to 22.5 Dyn/cm, and make it spread on the polish plate equably. An anti-electrostatic solvent is also added to the slurry to avoid the magnetoresistance (MR) head being destroyed by electrostatic discharge. The anion concentration of the slurry is strictly controlled in ppb level so as to avoid the erosion of magnetic heads as shown in Table 5. The concentration of UFDs in the slurry is 0.4 wt %. 

Localization of both the write fields and read head sensitivity is achieved by positioning both the write head and read head sensor in very close proximity of the disk surface. The heads are bonded to the rear end of a slider that skims across the disk surface on a thin layer of air entrained by the rotating disk. Thus, the operation of a disk drive reqnires a delicate balance of mechanical, electrical, and magnetic properties, with all three optimized for both economy and performance. 

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