Engineering all-optical magnetic recording
Heat-assisted magnetic recording (HAMR), the process of heating the magnetic medium to enhance its magnetic properties while writing is a promising but technically difficult solution. Scientists studied all-optical magnetisation switching in nano-structured materials to improve the recording density. With EU funding, the project OP2M (Optical probe and manipulation of magnetization at the nanometer scale) brought together world-class scientists from Europe and the United States. The scientists used ultrashort laser pulses to probe and manipulate magnetisation at very small spatial scales and very fast temporal scales. Femtosecond laser pulses can reverse magnetisation 1 000-10 000 times faster than magnetic fields or spin-polarised current pulses, and is reportedly a highly energy-efficient process. Therefore, research work focused on ultrafast magnetisation dynamics on the nanoscale and all-optical magnetisation switching. The OP2M project's ultimate goal was to engineer materials for all-optical magnetisation switching with no applied magnetic field. Project scientists demonstrated that all-optical magnetisation switching can be achieved in more than just a few rare earth transition-metal alloys. The OP2M team showed the phenomenon in a variety of materials including alloys, multi-layers and synthetic ferromagnets. A major breakthrough was all-optical magnetisation switching achieved for the first time in a rare-earth-free heterostructured system. Specifically, more than 30 different alloys have been grown by sputtering heavy rare earth elements and transition metals on a glass and tantalum (Ta) substrate. To demonstrate that the phenomenon is not unique to rare earth-based materials, they also fabricated synthetic ferromagnetic heterostructures. OP2M project results have significantly increased our understanding of the underlying mechanisms involved in all-optical magnetisation switching. More importantly, this new knowledge is expected to facilitate the engineering of materials that can be magnetically switched by all-optical means using well-established thin-film techniques. This project has shaped a new role for HAMR in future magnetic memory devices.
Keywords
Magnetic memory devices, heat-assisted magnetic recording, all-optical magnetisation switching, nano-structured materials, rare earth