Spins in Motion Photoemission

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Spins in MotionPhotoemission Electron
Transmission Through a Ferromagnetic Film

• Jürgen Henk, Peter Bose, Thomas Michael Patrick
  Bruno

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• Background Spintronics with Nanodevices
• Importance of spin-dependent electron scattering
  at interfaces in ultrathin magnetic films
• Microscopic probes From e-motion to spin motion
• Electron transmission through freestanding films
  (standard technique)
• Spin-polarized LEED

What is spin motion? Can we investigate it by
photoemission?
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Spin motion Scattering at a Magnetic Quantum Well
Incoming spins normal to the magnetization

• Two characteristic wavelengths
• Precession about 200 ML
• Multiple scattering about 4-5 ML
• Inelastic scattering Relaxation towards the
  magnetization

Inelastic
Elastic
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What about Photoelectron Spectroscopy?
2. Transmission through an Fe film
3. Spin-resolved detection
Idea
1. Excitation of Pd-core levels
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• Ingredients
• Source of spin-polarized electrons
• Spin-orbit coupling polarized light
• Source of spin-dependent scattering
• magnetic film
• Spin detector
• Mott or SPLEED detector

• Problem Small photoelectron escape depth ?
  restriction to ultrathin films
• A complete precession cannot be observed
• The relaxation limit cannot be reached
• The spin motion might be governed by the
  short-period oscillation

Results for Fe/Pd(001) Theoretical Experiments
Model Calculations
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Fe/Pd(001) Elastic Inelastic Scattering 17.5
eV kinetic energy Transmitted ESP vs Fe coverage
Ab initio results confirmed by the quantum-well
model
Inelastic P relaxes towards the magnetization
(increasing P_x)
Elastic P_x does not increase
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Model Calculation Effect of the Electronic
Structure Three-band nearly-free-electron model
with inelastic scattering at an interface
Reduced transmission in one spin channel ?
modulation of the transmitted ESP at the band gaps
Evanescent states
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Fe/Pd(001) Effect of the Electronic
Structure Variable kinetic energy Fe coverage
Band gap in Fe
Few transmission channels ? monotonous behavior
Several transmission channels ? complicated
behavior
Onset of efficient transmission channels
Band gap in Pd
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• Concluding Remarks
• Spin motion can be investigated by SPARPES
• Advantages
• Easy orientation of the incident spin
  polarization
• No preparation of free-standing films (used in
  transmission experiments)
• Shortcoming Restriction to ultrathin films
• Information
• on electronic structure
• Tool for investigating magnetic configurations?
  Possibly noncollinear?
• See cond-mat/0211163