Enhanced Gilbert damping and role of metallic interfaces in large-angle spin precession

1
Enhanced Gilbert damping and role of metallic
interfaces in large-angle spin precession

• Christian Stamm, Ioan Tudosa, Frank King,
  Hans-Christof Siegmann, Joachim Stöhr
• Stanford Synchrotron Radiation Laboratory and
  Stanford Linear Accelerator Center, Stanford, USA
• Georg Woltersdorf and Bret Heinrich, Simon
  Fraser University, Burnaby, Canada
• Andreas Vaterlaus, Swiss Federal Institute of
  Technology, Zurich, Switzerland

Single Fe layer
Double Fe layer
Exciting the magnetization
Au 10 layers
Au 10 layers
Epitaxial growth on GaAs(001) FMR
characterization damping a 0.004 also measured
anisotropies MOKE hysteresis loop magnetized
in-plane 110 very soft! (HC 12 Oe)
Fe 15 layers
Fe 10 or 15 layers
constant current alignment parallel to
field pulsed current (5 ps) precessional
switching
GaAs
Au 40 layers
Fe 40 layers

• 4-fold wins over uniaxial
• easy-axis rotated 45
• pattern more complicated

GaAs
The magnetic field pulse
Magnetic imaging
SEMPA images
top layer 15 ML Fe huge pattern is consistent
with low anisotropy bottom layer 40 ML Fe
SEMPA images of M (SEM with Polarization
Analysis) one magnetic field pulse 10 ML Fe /
GaAs (001)
Generated by relativistic electron bunch at the
Final Focus Test Beam of the Stanford Linear
Accelerator
50 mm
M0
Peak field of 7.5 Tesla 10 mm away from center,
falling off with 1/R
1 mm
50 mm
50 mm
Relaxation
Dynamic motion of M
Conclusions
After field pulse damping causes dissipation of
energy during precession fit using LLG
equation anisitropies same as FMR but damping a
0.017 4x larger

• field pulse lifts M out of plane, deposits energy
  as demagnetizing field
• precession switches M
• relaxation by damping
• Landau-Lifshitz-Gilbert

in-plane M

• Strong, ultrashort field pulse excites
  magnetization precession and relaxation
• Ultrathin Fe layer damping 4x larger than in
  FMRpossibly due to spin-currents across
  interface into paramagnet (enhanced for
  large-angle precession)Tserkovnyak, Brataas,
  BauerPhys Rev Lett 88, 117601 and B 66, 060404
  (2002)
• Fe double layer complex patterndynamic exchange
  coupling via spin currents?Heinrich et al., Phys
  Rev Lett 90, 187601 (2003)

M
H
lines of constant (initial) torque MxH
(energy barrier for switching KU)