Theoretical considerations for extremely high-density perpendicular recording

Recording media experience the superparamagnetic effect as a fundamental limit. To achieve a maximum signal-to-noise ratio, SNR, the grains in the media need to be as small as possible. Very small grains are susceptible to thermal instabilities if the magnetic energy that resists magnetization reversal, is too small when compared to the thermal energy. Within the constraint of thermal stability and write-ability, the SNR of longitudinal media can no longer be advanced significantly. These difficulties have prompted a renewed interest in perpendicular recording. Perpendicular recording faces the same fundamental problem: the generation of SNR under the constraint of adequate write-ability and thermal stability. The most promising design of a perpendicular recording system uses a magnetically soft underlayer (SUL), which enhances the recording field. A proper analysis of the two recording modes, longitudinal and perpendicular recording with a pole head, is very complex and has been attempted recently. The analysis has shown that the recording potential of the two modes is roughly similar, although it has to be remarked that perpendicular recording media are more exchange tolerant than longitudinal media and hence it may be conjectured that more of the recording potential can be achieved in practice. To accomplish extremely high-density recording, it is therefore required to achieve a high recording field together with a more favorable recording geometry.