Ultrafast Demagnetisation at 20

Program Description

First discovered in 1996, ultrafast demagnetisation has sparked a wide variety of research in magnetism on the femtosecond timescale. The effect observed was that the elemental ferromagnet nickel demagnetises by a considerable amount (>30%) upon excitation by an ultrashort IR laser pulse. This result was seminal because it suggested the possibility of controlling magnetisation many orders of magnitude faster than the damped-precession techniques used in standard magnetic data storage. This talk will sketch some of the developments in experiment and theory since then, before discussing a current result on ultrafast switching. Finally, we will go full circle and come back to the current status of our understanding of ultrafast demagnetisation in the elemental ferromagnets iron and nickel. Despite the experimental progress in the last 20 years and studies of more complex magnetic materials, the explanation of the original effect has still not been settled. In a sneak preview of our upcoming experiment at XPP (LCLS), a possible new piece of the puzzle will be discussed.