Spacing Control in Heat-Assisted Magnetic Recording

The spacing between the flying head and the rapidly rotating disk in hard disk drives continues to decrease in order to grow the areal density. In heat-assisted magnetic recording (HAMR), the spacing control complexity is compounded by the additional protrusion resulting from the laser heating. Compared to the writer induced and thermal fly-height control protrusion, the near-field transducer (NFT) protrusion is a faster and more local protrusion that requires new HAMR-specific spacing control techniques. In this paper, we will review the simulation and experimental studies which shed light on both the steady-state and transient characteristics of the NFT protrusion. Simulation analysis reveals the scale of the protrusion and its effects on spacing control. Experimentally, we have demonstrated a novel technique to characterize the NFT protrusion and assist in setting the spacing for each HAMR head. Based upon the knowledge gleaned from characterization, compensation schemes have been developed. Some of the schemes have already been successfully demonstrated.