Zero-State Insert Dual-Layer HAMR Media Recording

Abstract

Heat-assisted magnetic recording (HAMR) can support extremely high areal densities based on the thermal stability argument. However, significant challenges remain to reduce switching probability distribution (SPD) to improve media SNR. Exchange coupled composite (ECC)-type architectures, such as the designs employed in perpendicular media, are being explored for HAMR media and show potential promise at reducing SPD. In this article, we propose a new approach for the media design that consisting of an exchange decoupled dual-layer HAMR media architecture. In this design, a few net zero magnetization state grains form near the transition resulting in a transition noise reduction when a small difference in a <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$T_{\text {c}}$ </tex-math></inline-formula> of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\approx 5$ </tex-math></inline-formula> % was applied between the two layers. A geometric 2-D recording model was used to explore this dual-layer media design space and transition noise response. The significant transition noise reduction under the grain size limit condition is attributed to a negative correlation between noise from the top and bottom layers. This simple model was supplemented with micromagnetic recording simulations that verify stable zero-state grains are established near the transition during the recording process. The simulations confirm the significant transition noise reduction, but an increase in the dc noise was observed. Once the dc noise was addressed by increasing the applied field magnitude, a significant SNR gain of 1.4 dB was achieved compared with the equivalent single-layer media.