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Perpendicular recording is one of the technology candidates to extend the areal density growth trend with the superior thermal stability and the high recording resolution. As we have experienced with longitudinal recording, noise originating from perpendicular recording also has a strong impact on the channel performance. In this study, the noise characteristics of the readout waveforms of a tri-layer perpendicular media and single-pole write/MR read heads were investigated using precise time-domain analysis. Waveform fluctuations were obtained by subtracting the ensemble-averaged signal from each measured noise-contaminated waveform. The time-domain analysis makes clear the dominant type of transition-related noise such as transition jitter, pulse breathing or dc noise, etc. It was revealed that the noise from perpendicularly recording medium concentrates at the center of written transitions. The dominant transition noise source was found to be the transition position jitter. The level of transition jitter of the perpendicular media used in this study was found to be comparable to that of 5 Gbpsi class longitudinal media. MFM measurements revealed that magnetization fluctuates in large size of about 80 nm, which results in the fluctuation of the transition centerline. Reducing transition jitter should be the focus of developing future high performance perpendicular recording media.

FeAlSi multi-layered structure successfully reduced the noise compared with a mono-layered film. Optical surface analyzer also revealed that the films did not show any clear magnetic domains of spike noise source in the whole disk. TEM image of low noise film showed wide grain boundaries between 200 to 500 nm diameter FeAlSi grain clusters. The coercivities of films were significantly reduced when they were laminated. Along with the cluster isolation effect, the interlayer magnetic coupling of the multi-layered FeAlSi films also effectively reduce the noise. Double-layered perpendicular medium with a CoPtCrO recording layer and a multi-layered FeAlSi soft under-layer showed 25.8 dB SNR at 400 kBPI and 0.36 m read truck width, and 2.5 10 7 BER on a spin stand was achieved.

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