BES - SLAC Group/Department Public Websites - Stanford University

FYO7 SLAC S CIENCE AND T ECHNOLOGY S ELF E VALUATION
development in magnetism and has been observed in resistance measurements. So far, however, the
nanoscale magnetization distribution during the switching process has remained hidden. We imaged
for the first time, the magnetic switching process using advanced pump-probe x-ray microscopy. We
observe that the switching process is initiated and determined by the lateral motion of a magnetic
vortex driven by the spin current. Motion pictures with 200 picosecond time resolution show that the
switching process is based on the motion of a magnetic vortex, leading to C-like patterns which may
decay later into a uniform magnetic state. Our measurements show the fundamental role played by
the curled Oersted field which necessarily accompanies the spin injection current.
Resonant X-ray Scattering: We plan to explore the nonperturbative x-ray probe limits in solids
using resonant soft x-ray scattering to determine the complex refractive index as a function of x-ray
pulse fluence. The resonant aspect of the x-ray scattering combines the structural with the electronic
and magnetic information of the system. The latter makes this technique highly sensitive to changes
in the electronic structure. The electronic structure responds to the excitation of core electrons and
the successive secondary processes on the time scales of the x-ray pulse duration (femtosecond
regime). We will investigate the earliest stages of radiation chemistry in liquids (primarily water),
extending from a few femtoseconds to many picoseconds. Prior pulsed electron beam studies of
radiolysis have not covered this temporal range, and the fs optical laser studies cannot produce the
electron cascade fundamental to the interaction of EUV/soft x-ray radiation in water.
Catalysis: The microscopic understanding of heterogeneous catalysis requires a detailed
understanding of the dynamics of elementary processes at surfaces including adsorption, formation of
different intermediates, and desorption, which can be stimulated by laser pumping and then probed
with XES or X-ray Photoelectron Spectroscopy (XPS) using FEL soft x-ray pulses. During the
reaction there are important charge and energy transfers between the different adsorbates and the
catalytic substrates that determine many of the important steps. Ultrafast pump (optical lasers) and
probe (FEL-XES, XPS) experiments can be used to identify short lived reaction intermediates,
inaccessible to a more conventional and static XES and XPS. From detailed knowledge of the
electronic structure, how the electrons flowed between the substrate and reactants can be derived and
related to changes in the nuclear coordinates.
Collaborations
PULSE has a very large number of active collaborations.
PULSE contributor: Y. Acremann;
Title: Magnetic Imaging;
Collaboration partners and institutions: Olaf Henrik, Hitachi, Steffan Eisebitt, DESY
PULSE contributor: A. R. Nielsson;
Collaboration partners and institutions: Prof. Lars G.M Pettersson, Stockholm University,
Sweden; Dr. Michael Odelius, Stockholm University, Sweden, Prof. Lars Ojamäe,
Linköping University, Sweden; Prof. Shik Shin, Tokyo University, Japan, Dr. Yoshi
Harada, Spring 8, Japan; Dr. Osamu Takahashi, Hiroshima University, Japan
PULSE contributors: Y. Acremann, H.C. Siegmann, J. Stöhr;
Title: Transformation of a Metal into an Insulator: Breakdown of Ohm’s Law in High
Electric Fields;
Collaboration partners and institutions: S. J. Gamble, Mark H. Burkhardt, SLAC, Stanford
University, and Department of Applied Physics, Stanford University,; Walter A. Harrison,
Department of Applied Physics,; A.B. Kashuba, Landau Institute for Theoretical Physics;
Rolf Allenspach, IBM Research, Zurich Research Laboratory; Stuart S. P. Parkin, IBM
Almaden Research Center.
PULSE contributors: Y. Acremann, H.C. Siegmann, J. Stöhr;
Title: Ultrafast High Resolution Magnetic Microscopy;
Collaboration partners and institutions: J. Katine, M.J. Ceary, Hitachi Global Storage, San
Jose; T. Tylisczczak, ALB Berkeley
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