Magnetic recording on co-alloy perpendicular multilayers
Ho, Kuok San
Lairson, Bruce M.
Doctor of Philosophy thesis
Perpendicular recording has the potential to achieve high-density data storage. As the linear density approaches to the superparamagnetic limit, traditional longitudinal recording may give way to perpendicular recording. This study investigated the possibility of using perpendicular multilayers as an alternative magnetic storage medium. Various cobalt based perpendicular multilayers were deposited. The macro-magnetic properties of the thin films were characterized using switching ratio and $\rm\delta M$ curves. The experimental measurements were correlated with the read/write recording tests. Medium noise analysis on perpendicular multilayers was performed in both time-domain and frequency-domain. The time-domain eigenvector expansion technique was adopted and extended for use in perpendicular recording. In addition, recording non-linearities from perpendicular multilayers have been measured by using pseudo-random binary sequence and the third harmonic ratio measurement. The readback non-linearity of MR head was characterized using a polynomial equation. Both the NLTS and partial erasure measurements show advantages for perpendicular recording compared to longitudinal. Finally, by constructing transformation filters, we demonstrated magnetic recording on perpendicular media via conventional longitudinal channels. A linear recording density of 204 kbpi has been obtained in a peak detection channel while a linear density of 350 kbpi was demonstrated on a partial response maximum likelihood (PRML) channel.