Magnetic Layers for Perpendicular Recording Media

Hard disk drives (HDDs) are recently being incorporated into video recorders, car navigation devices, family game machines, etc., as devices (AV-HDDs) to store digital AV (audio-visual) information such as movies and television programs. Because the AV-HDD has the features of large capacity, high speed and low cost, it is suitable for long-time recording, high-speed random access and multi-channel simultaneous recording and playback. The demand for AV-HDDs is anticipated to increase rapidly in the near future. In response to demands from this new market growing at a rate of 100 % per year, it is necessary to further increase the recording density, which is now at a level of 30 Gbits/in2 in mass production. Present HDDs utilize a longitudinal magnetic recording system in which the recorded magnetization is aligned in the film plane. If we increase the recording density of this system, the recorded magnetization becomes unstable due to the thermal energy at room temperature, thus creating the problem of thermal agitation of magnetization. Recently, a new recording system suitable for ultra-high density recording, i.e. a perpendicular magnetic recording system, has been attracting considerable attention, and this new system provides greater stability of the recorded magnetization as the recording density increases. Figure 1 is a schematic drawing showing the general layer structures and recorded magnetization for perpendicular magnetic recording media. Successive layers are stacked on the substrate in the order of soft magnetic underlayer, non-magnetic interlayer and magnetic recording layer for the storage. Because the recorded magnetization is aligned vertically, as opposed to longitudinally, the film structure and magnetic properties are quite different from those of the longitudinal magnetic recording media. To realize perpendicular magnetic recording media, it is essential to redevelop and redesign the film structure, thin film material and processing techniques. Of this group, the development of a high performance magnetic recording layer that retains the recorded magnetization is most important. Figure 2 shows several materials that may be used as the thin film material for magnetic recording layer such as CoCrPt alloy film, Co/X multilayer, amorphous film and FePt ordered lattice alloy film, depending on the applicable areal recording density. These materials each have their own characteristic microstructure, physical properties and, particularly, perpendicular magnetic anisotropy energy Ku. The material most suitable for the areal recoding density to be applied must be selected for the development of the magnetic recording layer. From early on, Fuji Electric started the development of perpendicular magnetic recording media to realize the next generation ultra-high density recording media and also initiated active joint research with