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Chappert - L'Electronique de Spin Claude CHAPPERT CNRS...

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L'Electronique de Spin Claude CHAPPERT, CNRS Département "Nanospintronique" Institut d'Electronique Fondamentale Université Paris Sud, Orsay, FRANCE [email protected]
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NTC2 - MESUREXPO 2006 2 Back to the basics Electrons carry a charge Î electronics e - l m ρ s m ρ atomic magnetic moments Î magnetic storage and a spin Î magnetism
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NTC2 - MESUREXPO 2006 3 From spin to magnetic storage basic energies in magnetism Exchange interaction quantum effect "magnetization" M in ferromagnets = magnetic moment per unit volume Magnetic anisotropy energy quantum relativistic effect tends to keep the spins parallel total energy changes with the orientation of M -90° 90° 180° 270° V K E = magnetic storage of binary information "0" "1" V M = µ ρ
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NTC2 - MESUREXPO 2006 4 The principle of magnetic storage I writing a "bit" magnetic track on a rotating disk microcoil ~ 120 atoms! abrupt magnetic "wall" ~500 atoms
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5 The first step of spin electronics 1988 : GMR discovered simultaneously by Fert et al . (Orsay) and Grünberg et al . (Jülich) 1988: The giant magnetoresistance (GMR) in magnetic multilayers ~ 80% Fe/Cr multilayers Fe Cr Fe R/R(H=0)
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6 The foundation of spin electronics "spin flip" scattering event <> : mean free path λ relaxation time τ spin diffusion length = sf sf τ λ λ 0 : spin mean free path sf sf l λ λ weak spin flip scattering rate (l sf >> λ ) Î "two channels" conduction model R R N. Mott, Adv. Phys 13, 325 (1964) electrons traveling inside conductors normal metals or R R R ferromagnetic metals: spin dependent λ
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7 Giant magnetoresistance in multilayers I parallel configuration antiparallel configuration R P < R AP / F F NM . .
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