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Gmr
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- 2. The Nobel Prizein Physics 2007The Nobel Prize in Physics 2007 Peter Grünberg “GMR can be considered one of the first real applications of the promising field of nanotechnology ” - Nobel committe Albert Fert
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- 4. Magnetic Forces Mathematically, FB= qv x B |FB| = |qv| |B| sin θ ( θ is angle between v and B) direction given by right-hand rule
- 5. Magnetic field pointinginto page (screen) Current-Carrying Wire Direction of velocity v of electrons Direction of force on conduction electrons
- 6. Magnetoresistance - MR Electrons - moving charges Effect of external magnetic field perpendicular to the flow Force due to field pushes electrons off track
- 7. Concept Behind GMR •GMR is a completely different effect from Magnetoresistance (MR) • MR is the regular “Lorenz” force on charges moving in a magnetic field • GMR exploits spin-dependent scattering
- 8. Spins and Scattering An electron moving into a magnetized region will exhibit spin-dependent scattering Scattering depends on direction of spin GMR is due to intrinsic rotation of the electron that induces a magnetic moment – the quantum mechanical property called spin
- 9. Resistance and magnetization Thestraighter the path of the electrons, the greater the conductance of the material. Electric resistance is due to electrons diverging from their straight path when they scatter on irregularities and impurities in the material.
- 10. Electron and itsspin •Two types of spin, spin up and spin down •Spin up exhibited by majority of electrons in ferromagnetic materials •Spin down exhibited by small amount of electrons •Spin up ultimately results in reduction in resistance, while spin down increases the resistance •Under the influence of external magnetic field most of the electrons will be showing spin up so that R reduces
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- 12. GMR Material No ExternalMagenetic field Resistance High External Magenetic field present Resistance low
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- 14. TMR from GMR Thetunnelling process dependent on the available electron states in the ferromagnetic materials Ni–SiO2films Fe/MgO/Fe
- 15. Merits • Dramatic Decreasein Price per GB of storage
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- 17. Limitations GMR applications arelimited to certain specific applications
- 18. GMR in HDDTechnology
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- 22. Outcomes of GMR •Discovery of GMR opened the door to a new field of science, magnetoelectronics (or spintronics) • CMR - Colossal MagnetoResistance, thousand-fold magnetoresistance in La–Ca– Mn–O • Magnetoelectronics & Nanotechnology.
- 23. SummarySummary • GMR effectswas discovered by A. FertA. Fert and P.P. GrünbergGrünberg independently. • GMR shows large magnetoresistance. – GMR ~50 % > MR ~ a few % • The greatest contribution of GMR is the sensitive reading head for HDD.
- 24. References • J.A. Katine,F.J. Albert, and R.A. Buhrman, “Current-Driven Magnetization Reversal and Spin-Wave Excitations in Co/Cu/Co Pillars” • www.isoloop.com • www.ieee.org • https://buffy.eecs.berkeley.edu/PHP/resabs
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