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Magnetization Dynamics: Nanosecond Magnetization Reversal

Magnetization Dynamics: Nanosecond Magnetization Reversal. J.-J. BOUZAGLOU. Outline. General concept Giant MagnetoResistance Magnetic Interactions Theoretical Magnetization dynamics Landau- Lifschitz -Gilbert Equation Spin Torque Effect Sample Structure Experimental Results

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Magnetization Dynamics: Nanosecond Magnetization Reversal

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  1. Magnetization Dynamics: Nanosecond Magnetization Reversal J.-J. BOUZAGLOU

  2. Outline • General concept • Giant MagnetoResistance • Magnetic Interactions • Theoretical Magnetization dynamics • Landau-Lifschitz-Gilbert Equation • Spin Torque Effect • Sample Structure • Experimental Results • DC Measurements • Pulse Measurements • Simulation

  3. Giant Magneto-Resistance (GMR) Discovered in 1988 Nobel Prize in 2007 λ =Mean free path Spin diffusion length Order of λ Scattering depend on the spin orbital

  4. Magnetic interactions (1/2) • Zeeman interaction • Exchange interaction • Magnetocristalline anisotropy • Shape anisotropy θ

  5. Magnetic interactions (2/2) • Energy • Effective Field • Torque

  6. Landau-Lifschitz-Gilbert Equation H • Newton second law • Field Torque • Precession • Damping Torque • Dissipation • Effective Field m

  7. soft layer Fixed layer Spin Torque H m Current induced magnetization reversal : Spin Torque term in LLG equation

  8. Sample Structure

  9. DC Measurements Hysteresis

  10. Current Sweep

  11. Phase diagrams Sample 24-19 ,100x100nm

  12. Phase diagrams Sample 29-19 ,100x100nm

  13. Pulse Diagrams

  14. Theoretical Fitting of Boundaries

  15. Extrapolated Critical Amplitude P->AP

  16. Extrapolated Critical Amplitude AP->P

  17. Theoretical Parameters

  18. Theoretical Parameters

  19. Dynamic Parameter P->AP

  20. Dynamic Parameter AP->P

  21. Theoretical Parameters

  22. Theoretical Parameters

  23. Simulation Sample 29-19 AP->P • Saturation Magnetization:Ms=713000 A/m • Volume: Thickness=1.6nmSurface=1e-14 m2 • Anisotropy axis: the easy axis is assumed to be along the direction perpendicular to the film plane. • Anisotropy constant: K=4.05 J/m3 • Damping parameter: Alpha=0.136 • Polarization of the current: P=0.164

  24. Pulse Boundaries

  25. Critical Amplitude

  26. Dynamic Parameter

  27. Conclusion • Ultrafast 200ps switching • Well defined switching boundary • Switching speed scales with I-Ic • Magnetic field strongly affects speed • Dispersion in extracted parameters show the limits of macrospin modeling=>Domain walls

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