All-Optical Switching: A Path to Recording Technology Beyond HAMR

After 20 years of development, heat-assisted magnetic recording (HAMR) is now entering production. Given the timescale associated with HAMR development, it seems important to consider the possibilities for future replacement. HAMR is limited by the phenomenon of “backswitching” which, in the limited write fields available to the HAMR process, leads to a reduction of switching probability: a reduction which becomes more pronounced as the grain size continues to decrease. An interesting possibility for technology beyond HAMR is all-optical switching (AOS), which is a field-free option thereby removing the need for an inductively generated head field. Since the AOS is driven by exchange, the effective fields involved are extremely large and the backswitching is dramatically reduced leading to more reliable switching. We review the underlying physics of the backswitching in terms of a “quadrilemma” and show how this is overcome by AOS. We also outline recent processes designed to switch ferromagnets and the usage of combined AOS/spin torque to achieve deterministic rather than the toggle switching exhibited by ferrimagnets. The conclusion is that any materials’ design must ensure a sufficiently large effective field to overcome backswitching.