Achievement and expected issues in heat assisted magnetic recording

Abstract

The main goals in magnetic recording are the continuous increase of the areal recording density and the highest possible signal-to-noise ratio (SNR). The conventional magnetic recording has approached its physical limits. Further growth of the areal density is limited by the superparamagnetic effect and by the limited possibilities to further improve write heads design and pole materials in order to enhance the writing field. The perpendicular magnetic recording (PMR) with pole head and perpendicular media is the best alternative, especially to defer the superparamagnetic limit. PMR is also better situated to face the challenging design trilemma of magnetic recording: To increase the areal recording density, smaller grain volumes are needed, but to ensure the thermal stability of recorded information, the anisotropy should be increased accordingly; or, the increased anisotropy asks for higher writing fields, which are unavailable with the saturation magnetization of the magnetic materials of the current heads. Obviously, an alternative technology is needed to overcome the physical limit of conventional perpendicular recording (CPR). The most promising successor of CPR is the heat–assisted magnetic recording (HAMR), which is a multidisciplinary technology, a combination of magnetic and optical recording technology that proved experimentally areal densities of more than 1 Tb/in2 . HAMR allows the use of very smallgrain media, required for recording at ultra-high densities, with a larger magnetic anisotropy at room temperature, thus assuring a good thermal stability, while the local heating leads to a temporary magnetic softening of the medium. The realization of HAMR involved some challenges from both optical design and media properties. In the optical design the use of near-field transducers (NFT) represents an important advance. Regarding the media, a thermal design was used to produce the heating and cooling of the media within a very short time, about 1 ns, in order to achieve the desired data rate and generate a large thermal gradient for sharp bit edge definition. The structure of a HAMR system is briefly discussed, as well as the processes characterizing the writing process. A special attention is paid to the requirements for the materials needed for this type of recording: the granular L10-ordered FePt:X alloy sputtered on glass disk, the FePt-C and FePtC-Ag granular films and the bitpatterned media. Some important challenges of the HAMR technology are also summarized.