Weighting a Domain Wall

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Weighting a Domain Wall

• Journal Club
• February 15 2005
• Current-Induced resonance and mass determination
  of a single magnetic domain wall, Nature 432, 203
  (2004)
• Elji Saitoh, Hideki Miyajima, Takehiro Yamaoka
  and Gen Tatara

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Motivation

• Fundammental Phyics interaction between currents
  and Domain Walls
• Great Experiment
• Opens INTERESTING QUESTIONS (Related to our
  future work)
• Related to some of my recent work
• JFR, M. Braun, A.S. Núñez, AH. MacDonald Phys.
  Rev. B 2004
• J. J. Palacios, D. Jacob, JFR, cond-mat/2004
• L. Brey, C. Tejedor, JFR, APL 2004

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What is a Domain Wall (DW)
Ferromagnetic Ground State. Good for local
EXCHANGE. BAD for Magnetostatics
Ferromagnetic DOMAIN EXCHANGE ok except in the
WALL GOOD for Magnetostatics
DOMAIN and GROUND STATE ARE TOPOLOGICALLY
DIFFERENT
DOMAIN WALL
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DW Thick or Thin
COMPETION between EXCHANGE and anisotropic
interactions
Exchange favors thick DW Anis. Int. Favors thin
DW
Thick DW
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Domain Wall Motion
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Domain Wall Motion
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Domain Wall Motion
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The Experiment
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Justification of
x
y
Clockwise
?
Anti- Clockwise
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LATER

• Why a DW can be considered a particle with mass?
• What is a magnetic charge?

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MagneticForceMicroscopy
Resistance vs a.c. frequency
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Resistance vs a.c. frequency
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mDW(6.55- 0.06 ) 10-23 Kg
                                                
                          ,
Is spin current f frequency m DW mass, ? DW
relaxation time
n conduction electron density RDW DW
resistance I total current
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DW From Field to Particle
M,x, F(x)

• PAPERS
• S. Takagi and G. Tatara, Phys. Rev. B 54, 9920
  (1996).
• H-B. Braun and D. Loss, Phys. Rev. B 53, 3237
  (1996)
• P. C. E. Stamp, Phys. Rev. Lett. 66, 2802 (1991).
  
• E. M. Chudnovsky, O. Iglesias, and P. C. E.
  Stamp, Phys. Rev. B 46, 5392 (1992). .

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DW From Field to Particle
Classical Lagrangian of a Field
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DW mass
Magnetic Charge
Magnetic Energy
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Magnetostatics
Magnetic Charge
Polarization Charge
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DW theory
EXCHANGE
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