Magnetic recording has been the dominant recording technology for information storage since the invention of the computer. Currently, 1-Gbit/in. longitudinal magnetic recording (LMR) systems have been realized and densities of 10 Gbit/in., having bit areas less than 0.1 μm, are being developed. To reach this goal, a drastic scaling down of the track pitch, bit-cell length, head gap, medium thickness, and head-medium spacing is required. If this trend of increasing densities continues, an areal density of more than 300 Gbit/in. is predicted in the 21st century, based on computer simulation using the perpendicular magnetic recording (PMR) mode instead of the current LMR scheme. Magnetic-recording technologies and related materials have already been discussed in another issue of the MRS Bulletin, and hence in this paper, we concentrate on Co-Cr-X material used as a medium for PMR.The PMR mode has been studied since 1975 and at present, Co-Cr-X (e.g., X = Ta) films with perpendicular anisotropy are the most promising media material. In general, such media should have the following properties: easy axis of magnetization perpendicular to the film plane, suitable coercivity (Hc) and remanent magnetization (Mr) for storing the information and reading it at a high signal-to-noise (S/N) level, uniform columnar size with a small diameter, magnetically uncoupled columns having a magnetization reversal based on rotation instead of a domain-wall motion, chemical stability under various environmental conditions, and a small surface roughness. In order to achieve the desired magnetic anisotropy and coercivity, a columnar morphology (small diameter) with an hep [0001] texture and exchange-decoupled, columnar boundaries—to create a magnetic microstructure for single domain switching columns with high coercivity—should be obtained. An overview of the preparation, microstructure, and magnetic properties of Co-Cr thin films is given in Reference 8. Depending on the deposition parameters, a so-called initial layer (with an in-plane magnetization) can be present.
Technologies for Image Information Storage. Bit Density Dependence of NLTS in Perpendicular Magnetic Recording.
