Numerical Analysis on Cross-Track Characteristics for Tracks Recorded with Microwave Assistance

Abstract

Several methods including energy assisted magnetic recording schemes have been proposed for solving the writability problems in magnetic recording. In these recording schemes, microwave-assisted magnetic recording[1] has recently attracted much attention for future ultra-high density recording. The effects of microwave assistance for the magnetization reversals closely relate with magnetic resonance phenomena which is strongly affected by damping constant of recording layer. In this study, recording performance was numerically estimated using micromagnetic simulations through signal to noise ratios (SNR) assuming an exchange-coupled composite (ECC) structured medium and cross-track SNRs were profiled. A 30-nm-track-wide asymmetric structured recording head with a spin torque oscillator designed for shingled magnetic recording was employed for recording simulation and a 17-nm-track-wide MR sensor was assumed in the reading processes. $H_{\text{k}}$ and $M_{\text{s}}$ for the soft section of the ECC medium are 17.5 kOe and 850 emu/cc, and those for the hard section are 80 kOe and 650 emu/cc. The damping constant of the hard section is set to 0.2. Figure 1 shows cross-track profile of the SNRs as a function of damping constant of the soft section. Microwave frequencies have been preliminary optimized for corresponding damping constant. Asymmetric profiles come from the asymmetric head field distributions and the highest SNRs are obtained at around +5 nm in the off-track position for any damping constants. The result also shows the highest SNRs tend to slightly increase with the damping constant of the soft section.