Perpendicular media signal and noise analysis by magnetic force microscopy on written transitions (abstract)

We have quantitatively analyzed the signal and noise properties of perpendicular media from magnetic force microscopy images of written transitions. Four sets of Pt/CoCrTa multilayer thin films were prepared under different sputtering conditions to yield virgin media domain sizes ranging from 50 to 5000 nm. The magnetic recording transitions on each disk were written in the frequency range from 2 to 30 MHz, which corresponds to recording densities from 20 to 300 kfci. We performed Fourier analysis on the written and unwritten areas of the media to obtain signal and noise spectra. The media noise and signal-to-noise ratios from these spectra are comparable with those from recording head read-back spectra. These spectra are indicative of the exchange coupling existing in the films and correlate with the synthesis conditions for the various media. By analyzing the unwritten areas in the sample disks, we also obtained the average virgin domain sizes for these four kinds of disks.