Perpendicular Magnetic Recording Medium for a Density Beyond 1 Tera Bit/inch2

Abstract

Perpendicular magnetic recording was proposed by Professor S. Iwasaki in 1977 [1] as a scheme superior to that of longitudinal recording in terms of high density recording performances. The new HDD (hard disk drive) system of perpendicular recording was commercialized in 2005. The area recording density started at 133 Gbit/inch2 [2], which far surpassed the achieved density of the conventional HDD of longitudinal recording. In 2006, successful demonstrations of the highest density at around 350–420 Gbit/inch2 were announced, one after another, by HDD manufacturers [3]; no other new information storage technology superior to magnetic recording has been proposed as yet. Thus, perpendicular recording is expected to dominate over the existing information storage technology in the near future. Perpendicular magnetic recording (PMR) has the great advantages of a single pole high writeability of recording in the gap between the head and the medium soft under layer, a high recording resolution of anti-parallel magnetization transition with no demagnetizing field, and a high thermal stability with a rather thick recording layer, when compared with the longitudinal magnetic recording (LMR) used so far . These advantages in PMR and the lately diagnosed limitation of thermal stability of the LMR media accelerated the commercialization of PMR at around a density of over 100 Gbits/inch2,where the PMR media have a large-enough margin for the limit of thermal stability. Construction of the commercialized PMR system is based on the original principle of PMR, in which the combination of a single pole head and a composite medium with a soft magnetic back layer was essential. Presumably, however, as long as granular type media are used, even the PMR system would face thermal instability of the media or the restriction of writing by single pole heads when a high density over 1 Tera bits/inch2 is designed. The former issue can be answered by employing very high anisotropy energy materials such as Fe–Pt, Sm–Co, Fe–Nd–B, etc. But it means an extremely high switching field of such media; thus, the latter issue of head writeability would, in the final outcome, become very serious.