Workshop on Ultrafast Dynamics in Strongly Correlated Systems

Non-equilibrium electron and spin dynamics in magnetically ordered films probed by fs x-ray pulses

6 Apr 2011, 10:50

20m

ETH Zurich, Campus Science City, HIT Building

Talk Magnetism II

Speaker

Christian Stamm (Helmholtz-Zentrum Berlin für Materialien und Energie)

Description

Investigations of fs laser excited non-equilibrium states are performed using soft x-ray pulses with 100 fs duration from the BESSY II femtoslicing facility. Time-resolved x-ray absorption spectroscopy (XAS), x-ray magnetic circular dichroism (XMCD), and recently resonant x-ray diffraction enable detailed measurements of the dynamic properties of magnetically ordered systems. Tuning the x-ray energy to individual absorption edges we study the laser induced changes of the valence electrons by XAS. Circularly polarized x-rays are used in XMCD measurements to follow the sub-picosecond quenching of spin and orbital angular momentum through a sum rule analysis. In Ni we found a transient increase of the spin-orbit coupling just after laser excitation, which persists during the demagnetization process. An element-resolved measurement of the magnetization dynamics in NiFe results in two different time scales for the Ni and Fe spins, demonstrating the strong influence of the laser-induced non-equilibrium state onto the exchange interaction.