Experimental Study of Head-Disk Interface in Heat-Assisted Magnetic Recording

Abstract

Heat-assisted magnetic recording (HAMR) has been proposed to achieve magnetic recording density. In HAMR systems, a laser is used to locally heat the magnetic disk to the Curie temperature, which is ~ 400°C-600°C, to assist in the data writing process. The high temperature working condition is a great challenge for the head-disk interface. Lubricant can be depleted by evaporation or decomposition. The protective carbon overcoat can be graphitized and oxidized. The surface quality, such as its roughness, can be changed as well. The near field transducer (NFT) structure is also vulnerable under the large number of heating cycles. All of those effects of the heating will present challenges for the reliability of the HAMR performance. In this paper, an experimental HAMR platform is introduced. The free space laser exposure of the media is calibrated based on the magnetization decay of special data tracks. Lubricant loss is determined from the optical surface analyzer. The lubricant changes as a function of different thermal load cycles are investigated as well. The disk topography is measured by an atomic force microscope after the mobile lubricant is removed. The hard overcoat's topography dependence on the laser exposure conditions is also studied. With regard to the media disk, we establish three distinct laser power thresholds for lubricant loss, disk surface degradation, and magnetization decay. As the laser power increases, the lubricant starts to change first before the magnetization starts to decay, indicating that lubricant could be the most vulnerable component to the laser heating in HAMR systems. Then, the disk overcoat's surface changes, becoming rougher after the magnetization starts to decay. Furthermore, the lubricant degradation is more serious under cyclic loading conditions. With regard to the transducer, the metal film of the NFT gets removed due to high energy laser ablation, and then the NFT loses its capability to focus the light, as required for HAMR systems.