Tribological issues in perpendicular recording media

As the hard disk drive industry is transitioning from longitudinal (LMR) to perpendicular (PMR) recording, a new set ofreliability challenges had to be overcome. In particular, the magnetic media structure, which relies on well-segregated grains of6–10 nm diameter, can exhibit a rough structure, with peak-to-mean amplitude of 3–6 nm. In this paper, we will discuss how thistopography could affect the overall reliability of the head–disk interface. In the first part, we will illustrate the loss of adequatecoverage from the overcoat on PMR media, compared to the smoother LMR media, and we will attempt to quantify thetopography in terms of its deviation from a Gaussian height distribution. Particular emphasis will be given to surface outliers andtheir removal during the burnishing process. The second part will be devoted to the lubricant preferential migration to the grainboundaries, driven by surface tension. It will be shown by an EELS line scan that the lubricant film is indeed thicker in the valleysbetween the grains, in agreement with surface tension driven redistribution. Finally, we will demonstrate that the TouchdownHeight (TDH) of a PMR disk is 0.5 nm higher than its LMR counterpart, owing to its enhanced nano-roughness. Oncerecognized, these challenges can be overcome through a careful and thorough optimization of the various processing parameters,eventually leading to an overall reliability level equal or better than LMR media.KEY WORDS: magnetic data storage, magnetic data disks, nanotribology, corrosion