Analytical and micromagnetic-based modeling of quantization noise in MFM-based pulse-width-Modulation perpendicular recording

In this work, we present three magnetic force microscopy (MFM)-compatible pulse-width-modulation (PWM) coding scheme to be employed in scanning-probe storage devices. For each code, analytical models describing the code length utilization [CLU, i.e., non-return-to-zero (NRZ) code length to PWM code length ratio] and the signal-to-quantization noise ratio (SQNR) resulting from the granularity of the media are derived. To verify the models, a micromagnetic model was constructed. Using a proposed variable-length PWM coding scheme with 3 bits/symbol, 30-nm tip diameter, and a fractional step of 20% of the initial mark, a 82% increase in areal density over optimized regular NRZ single-bit coding is shown to be achievable (i.e., 1.26 Tb/in/sup 2/) with an SQNR of 17.2 dB and an overall SNR of 13.1 dB.