Giant Magnetoresistance(GMR) & Spintronics
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Transcript of Giant Magnetoresistance(GMR) & Spintronics
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GIANT MAGNETORESISTANCE
& APPLICATIONS
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ContentsIntroduction
Ferro magnetic materials
Spintronics Spin dependent conduction
Effect of Impurities
Interlayer Coupling
GMR
Schematics of Multilayer
Evidence of GMR
Tunnel Magnetoresistance
Application
Spin Valve
MRAM
Spin transistor
Future Works
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To begin we have to go back to 1857
In 1857 Scottish scientist William Thomson, who later becomes Lord Kelvin, discovers that the application of external magnetic field to a nickel (Ni) wire increases its electric resistance.
Names the Phenomenon 'Magneto-resistance'
The resistance was not lowered by more than 5%
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Remember Hall Effect!
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Ferromagnetic materials
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Spintronics
The idea in quantum physics that electrons have both Charge and spin.
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Spin Dependent Conduction in Ferromagnetic Materials
ρ↓
ρ↑Mott's Two Current model
Mott, Proc.Roy.Soc A153, 1936Fert et al, PRL 21, 1190, 1968
α=ρ↑ρ↓
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Effects of Impurities
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Interlayer Coupling
Transport of spin along the interfaces results in torque acting on the magnetization which is due to the fact that majority and minority electrons have different reflection coefficients at the interfaces. The torque alignes the magnetization according to the associated ratio of reflection coefficients
P.Grünberg, R.Schreiber, Y.Pang, M.B.Brodsky and H.Sowers, Phys. Rev.Lett. 57, 2442 (1986)
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Image courtsey nobelprize.org
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Schematic of Magnetic MultilayerFeFe
Cr
Formed using the Molecular beam epitaxial growth
Fe/Cr/Fe trilayer used by P. Grünberg
Fe/Cr/Fe multilayer used by A. Fert
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First Evidence of GMR
A. Fert and I.A. Campbell, “Two-current conduction in nickel” Phys. Rev. Lett. 21, 1190 (1968)G. Binasch, P. Grünberg, “Enhanced magnetoresistance in layered magnetic structures ”, Phys. Rev. B 39, (1989)
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Tunnel Magnetoresistance
Moodera et al, Miyasaki et al, 1995CoFe/AlO /Co, MR~30% - 40%
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Applications
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Read head of Magnetic Hard drive
Spin Valve Sensors
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CPP and CIP Geometry
Source: Seagate
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MRAM
Advantages:Low switching timeHigh data storage spaceLow power requiredNon-Volatile
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Spin transistorInitial design by Datta Das et. al. Improved by Mark Johnson
Datta, S and B. Das (1990). "Electronic analog of the electrooptic modulator"
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Future Works
Magnetic Switching transistors and Microwave Generation By Spin Transfer
Next generation of MRAM with precise addressing and low power requirement
Self synchronous Spin Transfer Oscillators(STO) with frequency control using Dc tuning
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Integration of Spintronics with semiconductors hybrid structures associating ferromagnetic metals with
nonmagnetic semiconductors. eg. Spin led, Spin solar cell fabrication of ferromagnetic semiconductors. Ga 1-x Mn x
As
In Bio-Medical Research
Future Works (Contd.)