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Magnetization dynamics
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Only x-rays combine sub-ns time resolution with sub 100nm spatial resolution!
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Magnetism: The reservoirs
Electrons Phonons
Spin
The fundamental interactions The micromagnetic picture
fs to ps dynamics Very complexTime scale: 100ps to years
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The two dynamic regimes
E. Beaurepaire, et al.,
Phys. Rev. Lett. 76, 4250 (1996)
Ultrafast demagnetization Precession and damping
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Time resolved MOKE
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The sample
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Direct observation of the precession
Y. Acremann et al., Science 290, p492 (2000)
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Magnetic eigenmodes
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Time Resolved Photo Emission Electron Microscope
Synchrotron radiation
Pump laser beam
Auston switch
Electron optics
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Response to the magnetic field pulse
Observation x-raysMagnetic field pulse(~300 ps in the beginning )
10 m
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Hidden Parameter in the Domain Structure
Choe et al., Science 304, 420 (2004).
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Vortex at the domain wall crossing
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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!
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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
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•Spatial resolution: 30nm
•Temporal resolution: 70ps
•Elemental selectivity
•Magnetic contrast
Scanning transmission x-ray microscopy (STXM)
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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)
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Switching of the vortex core
Van Waeyenberge et al., Nature 444, 461 (2006).