Impact of Media In-Plane Grains on HAMR Performance and THMap Metrics

An important source of noise in the Heat Assisted Magnetic Recording (HAMR) medium results from structure or magnetic defects of the FePt grains. One source of media noise is the in-plane grains with easy axes pointing in-plane instead of out-of-plane. While the presence of these grains has been established in literature through experiments, there is a lack of understanding of how these grains can impact the HAMR performance and THMap metrics. In this modeling study, we focus on the impact of in-plane grains first on the HAMR performance, by varying their proportion throughout the media and capturing the pre-channel and post-channel performance parameters. We extend this analysis using the THMap process to understand the effect of in-plane grains on magnetization mean, variance and the readback signal mean, variance. We also compare the signal, noise, low frequency SNR (LF SNR) and jitter captured through micromagnetic simulations with values obtained from an analytical DC noise model. Finally, we use analysis with correlation length for magnetization to explain the relationship of the magnetostatic interactions between grains and signal variance as a function of in-plane grains. This work establishes the performance impact of in-plane grains and highlights the need to carefully control the fabrication process to reduce their presence.