Ultrafast Magnetism on Elemental Time and Length Scales

Objectives:

  1. Revealing the ultimate speed at which magnetic order can be manipulated and eventually controlled.
  2. Obtain novel and fundamental knowledge about the microscopic processes responsible for magnetization dynamics on elementary length- and time-scales.
  3. Develop novel approaches for femtosecond laser control of magnetism.

In order to achieve these goals we employ the unique capabilities of the femtosecond slicing source at BESSY II Berlin – delivering femtosecond soft X-ray pulses with variable light polarization (see link Femtoslicing) – which provides the required element-specific information with femtosecond time resolution. In particular, we use time-resolved XMCD as a probing tool to obtain quantitative information on ultrafast dynamics of the spin and orbital magnetic moments as well as on the transient dynamics of the spin-orbit coupling and of the exchange interaction – the key ingredients governing the magnetic order. To monitor the elementary length scales pertinent to magnetization dynamics in highly non-equilibrium states i.e. comparable with the exchange length of 10 nm and below, we use X-ray scattering techniques at the synchrotron light sources and other large-scale facilities like the free-electron laser in Stanford (LCLS). It is important to note that the employed soft X-ray photon energy range cover the elemental absorption edges of the 3d transition metals (Fe, Co, Ni) as well as of the 4f elements (Gd, Tb, Dy etc), these being (among) the most relevant elements for magnetism.