Ultrafast Magnetization Dynamics of CoFe Alloys*

Understanding the ultrafast magnetization dynamics in a metal after laser heating is critical for many engineering applications, including nanoscale thermal engineering, photocatalysis, and spintronics. Despite the topic’s importance, and decades of study, fundamental questions about ultrafast magnetization dynamics remain unanswered.  In this talk, I discuss my group’s experimental work to answer the following question. Can we control ultrafast magnetization dynamics in metal alloys by using the effect of alloy composition on electronic band structure to control the strength of quasi-particle interactions? We performed a series of pump/probe experiments on Co_1-xFe_x alloys of their ultrafast magnetization dynamics, Gilbert damping, thermal conductivity, and more. We find the ultrafast magnetization dynamics in these alloys depends strongly on composition. Alloy compositions with weak electron-phonon interaction strengths are also observed to have distinct ultrafast dynamics and low Gilbert damping parameters. I conclude my talk by discussing the implications of our findings for ultrafast magnetic switching and THz spintronics.