Magnetization dynamics

Only x-rays combine sub-ns time resolution with sub 100nm spatial resolution!

Magnetism: The reservoirs

Electrons Phonons

Spin

The fundamental interactions The micromagnetic picture

fs to ps dynamics Very complexTime scale: 100ps to years

The two dynamic regimes

E. Beaurepaire, et al.,

Phys. Rev. Lett. 76, 4250 (1996)

Ultrafast demagnetization Precession and damping

Time resolved MOKE

The sample

Direct observation of the precession

Y. Acremann et al., Science 290, p492 (2000)

Magnetic eigenmodes

Time Resolved Photo Emission Electron Microscope

Synchrotron radiation

Pump laser beam

Auston switch

Electron optics

Response to the magnetic field pulse

Observation x-raysMagnetic field pulse(~300 ps in the beginning )

10 m

Hidden Parameter in the Domain Structure

Choe et al., Science 304, 420 (2004).

Vortex at the domain wall crossing

Response to a fast field pulseH

slow

fast (<1ns)

The response to a fast pulse is determined by the precession of the magnetization, not by relaxation!

Vortex moves parallel or antiparallel to the applied field direction

As the vortex drags the domain wall, it determinesthe dynamics of the whole domain structure!.

H

•Spatial resolution: 30nm

•Temporal resolution: 70ps

•Elemental selectivity

•Magnetic contrast

Scanning transmission x-ray microscopy (STXM)

Imaging magnetism with x-rays:X-ray Magnetic Circular Dichroism (XMCD)

Core Valence excitation of electrons

Polarization dependent absorption of x-rays

Depends on: number of holes, spin and orbital moment

Transition Metal (e.g. Fe, Co, Ni)

Switching of the vortex core

Van Waeyenberge et al., Nature 444, 461 (2006).