R&D: Performance Improvement of Dual STO Reading With AM–FM Combined Detection for 3D Magnetic Recording

IEEE Transactions on Magnetics has published an article written by Y. Nakamura, M. Nishikawa, and Y. Okamoto, Graduate School of Science and Engineering, Ehime University, Matsuyama, Japan.

Abstract: “3-D magnetic recording using microwave-assisted magnetic recording (MAMR) and a spin-torque oscillator (STO) for reading has been proposed as a candidate for prospective recording technologies. In 3-D magnetic recording using STO as a reading, the temporal magnetization dynamics of the STO has the fluctuations for frequency and amplitude which depend on the recorded pattern. In our previous work, we have constructed the STO signal model considering both amplitude and frequency fluctuations to develop a combined signal processing using the amplitude and frequency fluctuation detections. We have applied the STO signal model to the low-density parity-check (LDPC) coding and iterative decoding system with the individual detectors for amplitude modulation (AM) and frequency modulation (FM). Furthermore, we have reported that the dual STO reading system with only AM detection provides the improvement of the bit error rate (BER) performance. In this study, we propose the dual STO reading system with AM–FM combined detection in the hope that the finite impulse response (FIR) filter output distribution will be easier to detect with the decoder. We evaluate the BER performances of the proposed system for carrier-to-noise ratio (CNR S) of the system noise under an areal recording density of 1 Tbits/in² specification with bit-pattern medium stricture by computer simulation. The results show that the FIR filter output distribution for our proposed dual STO reading system at an FM detector output has become sharper, and the proposed system achieves the ‘No errors’ with CNR Sless by about 3.5 dB than the single STO reading system.“