All-Optical Control of Magnetization in various Ferromagnetic Structures*

Until recently, the only class of material that demonstrated all-optical switching (AOS) is a narrow range of rare-earth (RE) and transition-metal (TM) alloy compositions. However, recent experimental investigations have broadened the choice of materials for AOS and showed that optical control of magnetization is a much more general phenomenon. These materials include wide variety of ferrimagnetic RE-TM alloys, RE-free synthetic ferrimagnets and, moreover, ferromagnetic thin films, multi-layers and even their granular films. By employing a magnetization sensitive microscopy technique we investigated the AOS in various ferromagnetic materials like Co/Pt multi-layers as a function of material composition, structure, laser pulse fluence, and multi-layer thickness and also in FePt granular thin films, as a function of grain sizes. Our results show the optimal material conditions in ferromagnets and highlight pathways for reducing possible energy consumption for the AOS in these materials. Moreover, our time-resolved pump-probe measurements on CoPt thin films and their multi-layers reveal the ultrafast magnetization response to the 100 fs laser pulses and its role in AOS.