R&D: Two Articles on HAMR Technologies

R&D: Measured and Modeled Responses for HAMR Up to Ultra-high Areal Densities

Examine the behavior of readback waveforms as such extreme densities are approached

IEEE Transactions on Magnetics has published an article written by Roger Wood, Jonas Goode, Rick Galbraith, and Amirhossein Sayyafan, Western Digital Corporation, Irvine, California, USA

Abstract: “While current magnetic recording components are still far from able to support user areal densities of 10 Terabits per square inch (Tbit/in²), it is nevertheless instructive to examine the behavior of readback waveforms as such extreme densities are approached. Waveforms from a contemporary shingled Heat Assisted Magnetic Recording (HAMR) drive are captured and separated into linear and nonlinear signal components, inter-track interference, signal-dependent media noise, and head/electronic noise. These are tracked and compared with modeled behavior as the raw areal-density seen at the disk surface is gradually increased. The modeled signal and noise are based on the reader response being approximated as the difference of two two-dimensional Gaussians. The raw areal-density measurements range all the way from 1.5 Tbit/in² to 12 Tbit/in². At the extreme of 12 Tbit/in², the signal is still clearly identifiable and is well behaved with minimal distortion. It is however completely overwhelmed by high levels of stationary media noise and, to a lesser extent, inter-track interference and then head/electronic noise.“

R&D: Impact of Media In-plane Grains on HAMR Performance and THMap Metrics

Work establishes the performance impact of in-plane grains and highlights the need to carefully control the fabrication process to reduce their presence.

IEEE Transactions on Magnetics has published an article written by Niranjan A. Natekar, Pierre-Olivier Jubert, Terry Olson, Alexander Goncharov, Richard M. Brockie, and Kiwamu Tanahashi, Western Digital Corporation, San Jose, CA, USA.

Abstract: “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.“