High data rate degradation and medium thermal stability in ultra-high density magnetic recording.

摘要

In this dissertation, two major issues in the ultra-high density magnetic recording, the high data rate degradation and the medium thermal stability have been investigated. The high linear density together with the increasing rotational speed makes the high recording data rate inevitable. However, it has been found that the recording performance degrades at high data rates. While in order to maintain a sufficient signal-to-noise ratio (SNR) at high areal density, the grain size in the magnetic layer needs to be reduced, the small grain volume makes the magnetization data pattern in the media become unstable under thermal agitation and affect the lifetime of storage dramatically.;By directly measuring the recording bubble footprint, the dynamic recording process was first characterized. In the light of the dynamic recording process, a complete understanding of the overwrite degradation in high speed recording has been obtained. Correlating with the nonlinear head response, the recording degradations at high data rate have been systematically investigated. By comparing the recording characteristics using different drive current waveforms, the effects of the field rise time and the head saturation have been understood.;A novel spin-stand based technique has been developed to characterize the thermal stability of recording media. The statistics of effective energy barrier distribution have been obtained by directly measuring the remanent magnetization decay in a short time scale by applying proper reverse fields. The results also indicate that magnetic interactions have significant impact on energy barrier distribution and the magnetization decay process. To study the effect of magnetic interactions on the media thermal stability, a statistical model, which takes into account the magnetic interactions, has been developed. The effective energy barrier has been found to be reduced by the presence of interactions. Increasing the exchange coupling helps to improve the thermal stability of the recording medium. A non-zero weak exchange coupling may be desirable considering both medium SNR and thermal stability. The impacts of the medium orientation and the grain size distribution have also been studied.