Ultrahigh density recording: Heat assisted or temperature assisted Magnetic Recording

Heat assisted magnetic recording (HAMR, Seagate acronym) or temperature assisted recording (TAR, Hitachi acronym) involves localized thermal heating of the media before the writing process. It is well known that the magnetic properties such as coercivity, saturation magnetization, magnetic anisotropy, and anisotropy field decreases with increasing temperature above room temperature for a ferromagnetic material. Particularly, the magnetic anisotropy constant decreases with increasing temperature at a faster rate than the magnetization. This leads to a reduction in the anisotropy field and coercivity with increasing temperature, as shown in Figure 40.3. Figure 40.4 depicts the writing scheme of the HAMR/TAR. Since the temperature raise in the materials decreases the magnetic parameters, the general idea is to heat the localized zone of the medium using a laser spot during the writing process such that the coercivity of the medium comes down to level of head fields. After the writing process and when the materials come back to room temperature, the material presents high anisotropy values and correspondingly, large thermal stability. This would allow increasing the recording capability by the factor of 100, i.e., the areal density of above 50 Terabits/inch² . Although the HAMR technology has ability to write high anisotropy materials, this technology requires number of novel components, such as controlling Curie temperature in medium, light delivery system, the thermomagnetic writer, a robust head disk interface, and high anisotropy media with proper thermal design. Also, designing these components into a high performance data storage system requires system level optimization. Hence, this technology poses a number of technical challenges that must first be addressed before the industrialization.

Figure 40.4: Schematic picture of the HAMR/TAR writing.