DW dynamics in nanostrips: motivationsDW dynamics in a disordered nanostrip
Domain wall dynamics in disordered magneticnanostrips
B. Van de Wiele1, L. Laurson2, G. Durin3,4
1Dep. of Electrical Energy, Systems and Automation, Ghent Univ., Belgium2Dep. of Appl. Physics, Aalto Univ., Finland
3ISI Foundation, Torino, Italy4INRIM, Torino, Italy
talk@Jems - Parma - Sept. 12, 2012
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DW dynamics in nanostrips: motivationsDW dynamics in a disordered nanostrip
Outline
1 DW dynamics in nanostrips: motivationsDW for spintronics devicesRole of disorder in DW dynamics
2 DW dynamics in a disordered nanostripLandau-Lifshitz (LL) equation on permalloy stripsDynamics under applied magnetic fieldsDynamics under spin-polarized currents
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DW dynamics in nanostrips: motivationsDW dynamics in a disordered nanostrip
DW for spintronics devicesRole of disorder in DW dynamics
Tame the stochastic nature of DW dynamics
Racetrack memory (2008) Magnetologic memory (2005)
DW oscillator (2008)
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DW dynamics in nanostrips: motivationsDW dynamics in a disordered nanostrip
DW for spintronics devicesRole of disorder in DW dynamics
Disorder as rough wire edges
Turbolent DW motion:no Walker breakdown
Main conclusion...Roughness should rather be engeneered than avoided
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DW dynamics in nanostrips: motivationsDW dynamics in a disordered nanostrip
DW for spintronics devicesRole of disorder in DW dynamics
Disorder as fluctuation of magnetization
Main conclusion...Effective damping increasing with disorder content.
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DW dynamics in nanostrips: motivationsDW dynamics in a disordered nanostrip
DW for spintronics devicesRole of disorder in DW dynamics
Disorder enhances stochasticity of DW motion
Main conclusion...Dynamic DW pinning enhances stochasticity
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DW dynamics in nanostrips: motivationsDW dynamics in a disordered nanostrip
Landau-Lifshitz (LL) equation on permalloy stripsDynamics under applied magnetic fieldsDynamics under spin-polarized currents
The LL equation with random non-magnetic voids
The LL equation with the spin-transfer torque terms,
∂M∂t
= − γ
1 + α2 M×Heff (1)
− αγ
Ms(1 + α2)M× (M×Heff )
−bj
M2s (1 + α2)
M× (M× (j · ∇)M)
−bj
Ms(1 + α2)(ξ − α)M× (j · ∇)M,
where Heff is the effective magnetic field, γ is the gyromagneticratio, α is the Gilbert damping constant, ξ is the degree ofnon-adiabaticity, j is the current density, andbj = PµB/(eMs(1 + ξ2)), with P the polarization, µB the Bohrmagneton and e the electron charge.
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DW dynamics in nanostrips: motivationsDW dynamics in a disordered nanostrip
Landau-Lifshitz (LL) equation on permalloy stripsDynamics under applied magnetic fieldsDynamics under spin-polarized currents
GPU-accelerated micromagnetic simulations
Mumax• Finite-difference discretization• Landau-Lifshitz formalism• Spin-transfer torque (Zhang-Li and Slonczewski)• Finite temperature• Space- and time-dependent input parameters• GPU speedup up to 100x compared to CPU• Optional periodic boundary conditions• Flexible Python input files• Cross-platform and Open Source
Visit url: http://code.google.com/p/mumax2/
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DW dynamics in nanostrips: motivationsDW dynamics in a disordered nanostrip
Landau-Lifshitz (LL) equation on permalloy stripsDynamics under applied magnetic fieldsDynamics under spin-polarized currents
Simulation of DW dynamics in Permalloy nanostrips
Simulation parametersMaterial• thickness = 10 nm, width = 100 nm• lenght = 3.2 µm (field), lenght = 6.4 µm (currents)
Disorder as a distribution of voids• Size: 3.125 x 3.125 x 10 nm3 (1 cell columns)• Densities: 3125, 6250, 9375, 12500 voids/µm2
V-shapedtransverse DW
anti-vortex DW(core up)
anti-vortex DWs(core down) 9 / 14
DW dynamics in nanostrips: motivationsDW dynamics in a disordered nanostrip
Landau-Lifshitz (LL) equation on permalloy stripsDynamics under applied magnetic fieldsDynamics under spin-polarized currents
Simulation of DW dynamics in Permalloy nanostrips
Simulation parametersMaterial• thickness = 10 nm, width = 100 nm• lenght = 3.2 µm (field), lenght = 6.4 µm (currents)
Disorder as a distribution of voids• Size: 3.125 x 3.125 x 10 nm3 (1 cell columns)• Densities: 3125, 6250, 9375, 12500 voids/µm2
V-shapedtransverse DW
anti-vortex DW(core up)
anti-vortex DWs(core down) 9 / 14
DW dynamics in nanostrips: motivationsDW dynamics in a disordered nanostrip
Landau-Lifshitz (LL) equation on permalloy stripsDynamics under applied magnetic fieldsDynamics under spin-polarized currents
Perfect vs disordered wires under magnetic fields
H
PERFECT DISORDERED
What’s new: Walker breakdown shifted,10 / 14
DW dynamics in nanostrips: motivationsDW dynamics in a disordered nanostrip
Landau-Lifshitz (LL) equation on permalloy stripsDynamics under applied magnetic fieldsDynamics under spin-polarized currents
Perfect vs disordered wires under magnetic fields
H
PERFECT DISORDERED
What’s new: Walker breakdown shifted,10 / 14
DW dynamics in nanostrips: motivationsDW dynamics in a disordered nanostrip
Landau-Lifshitz (LL) equation on permalloy stripsDynamics under applied magnetic fieldsDynamics under spin-polarized currents
Perfect vs disordered wires under magnetic fields
H
PERFECT DISORDERED
What’s new: Walker breakdown shifted, DW core pinning10 / 14
DW dynamics in nanostrips: motivationsDW dynamics in a disordered nanostrip
Landau-Lifshitz (LL) equation on permalloy stripsDynamics under applied magnetic fieldsDynamics under spin-polarized currents
DW velocity vs magnetic field
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DW dynamics in nanostrips: motivationsDW dynamics in a disordered nanostrip
Landau-Lifshitz (LL) equation on permalloy stripsDynamics under applied magnetic fieldsDynamics under spin-polarized currents
DW velocity vs magnetic field
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DW dynamics in nanostrips: motivationsDW dynamics in a disordered nanostrip
Landau-Lifshitz (LL) equation on permalloy stripsDynamics under applied magnetic fieldsDynamics under spin-polarized currents
Applied current, adiabatic ST, the results
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DW dynamics in nanostrips: motivationsDW dynamics in a disordered nanostrip
Landau-Lifshitz (LL) equation on permalloy stripsDynamics under applied magnetic fieldsDynamics under spin-polarized currents
Applied current, non-adiabatic ST, the results
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DW dynamics in nanostrips: motivationsDW dynamics in a disordered nanostrip
Landau-Lifshitz (LL) equation on permalloy stripsDynamics under applied magnetic fieldsDynamics under spin-polarized currents
Maps of contributions
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