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A*STAR Singapore - Data Storage - Seed first, heat latter for better writing

DCN Corp® - A seed-then-heat-sink technique for heat-assisted magnetic recording media promises high signal-to-noise ratios.  Credit - © stevanovicigor/iStock/Thinkstock.A new technique for heat-assisted magnetic recording media promises improved writeability for next-generation hard drives

Heat assisted magnetic recording (HAMR) is a new process that realises the three goals of magnetic recording - readability, writeability and stability.  A*STAR researchers have now succeeded in improving such writeability by employing a thermal design that permits a higher density recording. [1]

HAMR magnetically records data using a laser to locally heat the area being written.  Careful control of the thermal spot size on the medium and the thermal gradient using writing allows more information to be written in a smaller area.  The recording medium's thermal profile is influenced by its physical and chemical properties, such as its optical characteristics, microstructure and layer structure, which impact the recording performance and density.

Jiang Feng Hu and his group from A*STAR Data Storage Institute wish to better control the thermal profile.  The three layers making up the writer layer - the heat-sink layer, underlayer and top layer - must support high thermal gradients.  In addition, the top layer should be crystalline with controllable microstructural features.  An L10-orderd iron-platinum alloy film is a popular top as it exhibits a high magnetic anisotropy.

However, being able to choose a suitable heat-sink layer is challenging.  For example, Copper (Cu) based materials are attractive due to their high thermal conductivity, but a mis-match between the structures of the crystalline layer and the underlying magnesium oxide limits the growth of the L10 phase.  Although this mis-match can be corrected by inserting a layer between the heat sink and the underlayer, doing so reduces the thermal performance of HAMR media, so as explained by Hu - "This will produce a smaller thermal gradient and media signal-to-noise ratio (SNR),"  This is classed as being problematic as a high SNR is a critical measure of recording-media performance.

Hu's team focused on a technical solution called the 'seed-then-heat-sink approach' and corresponding media design.  As this design does not require an additional layer, it attains a large thermal gradient and a higher media SNR.  A textured Copper Nitride (Cu3N) film is used as a seed layer to induce an orientation of Magnesium Oxide (MgO) that promotes L10-ordered Iron-Platinum (Fe-Pt) film growth.  The resultant deposition of the Fe-Pt alloy film, as a high temperature process, decomposes Cu3N into Cu, which provides a suitable heat-sink layer.

Hu stated how this approach enables a large thermal gradient during the writing process - "This large thermal gradient is critical to the Fe-Pt based medium for HAMR application, especially for HAMR media with smaller grains to support the ultrahigh areal density that HAMR technology is targeting," Original article available here

The above A*STAR milestone highlights the reduction in steps gained from nano-scale dip coating.  Plus the ability to homogenously dip coat at Room Temperature and Pressure should enable for substantive mass manufacturing savings.  Going forward, if you and/or your colleagues are interested in making the above hypothesis reality - please ensure to contact the company as soon as practicably possible.

[1] Hu, J. F., Jian, Z. S., Tie, J. Z., Cher, K. M., Bao, X. X., et al. HAMR medium structure design and its process for excellent thermal performance. IEEE Transactions on Magnetics 50, 3201106 (2014). Journal citation available here