Optimizing the Optical and Thermal Design of Heat-Assisted Magnetic Recording Media

Abstract

An optimization study of heat-assisted magnetic recording (HAMR) media optical and thermal designs is presented. A simplified stack with five component layers is used, which allows a systematic exploration of their optical and thermal properties parameter space. The optimum HAMR media design maximizes the downtrack temperature gradient at a set target write width and for a laser power limited by the near-field transducer (NFT) lifetime. Best absorption results are obtained for plasmonic-like underlayer/heat sink and a recording layer with low refractive index and low extinction coefficient. This combination of optical properties leads to the optimum confinement of the electromagnetic field between the NFT and the lower interface of the recording layer. The optimal optical design is not sensitive to the three NFT designs considered and to the thermal optimization. For the thermal properties optimization, weighted gradient and power are introduced that account for the variations of recording velocity across the disk surface in 7200 rpm hard disk drives. The ideal thermal design contains a strong heat sink with an optimal effective thermal conductance heff between the recording layer and the heat sink. Sufficient thermal anisotropy is required in the recording layer to minimize the lateral heat flow in that layer. The optimum heff also depend on disk velocity and in-plane thermal conductivity in the recording layer. This paper also present the quantitative comparisons of different optical and thermal tradeoffs/variations that might be necessary in practical HAMR media designs.