05-04-2010, 10:56 AM
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Introduction to Spintronics
Electron has : Mass Charge Spin Spintronics=spin based electronics information is carried by spin not by
charge ferromagnetic metallic alloy based devices transport in fm materials is spin polarized
Introduction
Conventional electronic devices ignore the spin property
As electronic devices become smaller, quantum properties of the wavelike nature of electrons are no longer
negligible.
Adding the spin degree of freedom provides new effects, new capabilities and new functionalities
Information is stored into spin as one of two possible orientations
Advantages of spintronics
Non-volatile memory
performance improves with smaller devices
Low power consumption
Spintronics does not require unique and specialised semiconductors
Dissipation less transmission
Switching time is very less
compared to normal RAM chips, spintronic RAM chips will:
“ increase storage densities by a factor of three
“ have faster switching and rewritability rates smaller
Phases in Spintronics
SPIN INJECTION
SPIN TRANSFER
SPIN DETECTION
Spin injection
Using a ferromagnetic electrode
effective fields caused by spin-orbit interaction.
a vacuum tunnel barrier could be used to effectively inject spins into a semiconductor
back biased Fe/AlGaAs Schottky diode has been reported to yield a spin injection efficiency of 30%
By hot electrons
Spin Transfer
Current passed through a magnetic field becomes spin polarized
This flipping of magnetic spins applies a relatively large torque to the magnetization within the external
magnet
This torque will pump energy to the magnet causing its magnetic moment to precess
If damping force is too small, the current spin momentum will transfer to the nanomagnet, causing the
magnetization to flip
Spin detection
Optical detection techniques using magnetic resonance force microscopy
Electrical sensing techniques-through quantum dots and quantum point contact
SPIN RELAXATION
Leads to spin equilibration
T1-Spin-lattice relaxation time
T2-Spin-spin relaxation time
Neccesary condition 2T1>=T2.
Application GMR(Giant magnetoresistance)
Discovered in 1988 France
a multilayer GMR consists of two or more ferromagnetic layers separated by a very thin (about 1 nm) non-
ferromagnetic spacer (e.g. Fe/Cr/Fe)
When the magnetization of the two outside layers is aligned, resistance is low
Conversely when magnetization vectors are antiparallel, high R
Spin Valve
Simplest and most successful spintronic device
Used in HDD to read information in the form of small magnetic fields above the disk surface
Tunnel Magnetoresistance
Tunnel Magnetoresistive effect combines the two spin channels in the ferromagnetic materials and the quantum
tunnel effect
TMR junctions have resistance ratio of about 70%
MgO barrier junctions have produced 230% MR
MRAM
MRAM uses magnetic storage elements
Tunnel junctions are used to read the information stored in MRAM
MRAM
Attempts were made to control bit writing by using relatively large currents to produce fields
This proves unpractical at nanoscale level
MRAM
The spin transfer mechanism can be used to write to the magnetic memory cells
Currents are about the same as read currents, requiring much less energy
MRAM
MRAM promises:
Density of DRAM
Speed of SRAM
Non-volatility like flash
Spin Transistor
Ideal use of MRAM would utilize control of the spin channels of the current
Spin transistors would allow control of the spin current in the same manner that conventional transistors can
switch charge currents
Using arrays of these spin transistors, MRAM will combine storage, detection, logic and communication
capabilities on a single chip
This will remove the distinction between working memory and storage, combining functionality of many devices
into one
Datta Das Spin Transistor
The Datta Das Spin Transistor was first spin device proposed for metal-oxide geometry, 1989
Emitter and collector are ferromagnetic with parallel magnetizations
The gate provides magnetic field
Current is modulated by the degree of precession in electron spin
Current Research
Ferromagnetic transition temperature in excess of 100 K
Spin injection from ferromagnetic to non-magnetic semiconductors and long spin-coherence times in
semiconductors.
Ferromagnetism in Mn doped group IV semiconductors.
Room temperature ferromagnetism
Large magnetoresistance in ferromagnetic semiconductor tunnel junctions.
Future Outlook
High capacity hard drives
Magnetic RAM chips
Spin FET using quantum tunneling
Quantum computers
limitations
Controlling spin for long distances
Difficult to INJECT and MEASURE spin.
Interfernce of fields with nearest elements
Control of spin in silicon is difficult
please read
http://studentbank.in/report-spintronics--984
http://studentbank.in/report-presentatio...ics-theory
http://studentbank.in/report-spintronics
http://studentbank.in/report-relativisti...ics-theory
for getting more about seminar information of spintronics theory
Introduction to Spintronics
Electron has : Mass Charge Spin Spintronics=spin based electronics information is carried by spin not by
charge ferromagnetic metallic alloy based devices transport in fm materials is spin polarized
Introduction
Conventional electronic devices ignore the spin property
As electronic devices become smaller, quantum properties of the wavelike nature of electrons are no longer
negligible.
Adding the spin degree of freedom provides new effects, new capabilities and new functionalities
Information is stored into spin as one of two possible orientations
Advantages of spintronics
Non-volatile memory
performance improves with smaller devices
Low power consumption
Spintronics does not require unique and specialised semiconductors
Dissipation less transmission
Switching time is very less
compared to normal RAM chips, spintronic RAM chips will:
“ increase storage densities by a factor of three
“ have faster switching and rewritability rates smaller
Phases in Spintronics
SPIN INJECTION
SPIN TRANSFER
SPIN DETECTION
Spin injection
Using a ferromagnetic electrode
effective fields caused by spin-orbit interaction.
a vacuum tunnel barrier could be used to effectively inject spins into a semiconductor
back biased Fe/AlGaAs Schottky diode has been reported to yield a spin injection efficiency of 30%
By hot electrons
Spin Transfer
Current passed through a magnetic field becomes spin polarized
This flipping of magnetic spins applies a relatively large torque to the magnetization within the external
magnet
This torque will pump energy to the magnet causing its magnetic moment to precess
If damping force is too small, the current spin momentum will transfer to the nanomagnet, causing the
magnetization to flip
Spin detection
Optical detection techniques using magnetic resonance force microscopy
Electrical sensing techniques-through quantum dots and quantum point contact
SPIN RELAXATION
Leads to spin equilibration
T1-Spin-lattice relaxation time
T2-Spin-spin relaxation time
Neccesary condition 2T1>=T2.
Application GMR(Giant magnetoresistance)
Discovered in 1988 France
a multilayer GMR consists of two or more ferromagnetic layers separated by a very thin (about 1 nm) non-
ferromagnetic spacer (e.g. Fe/Cr/Fe)
When the magnetization of the two outside layers is aligned, resistance is low
Conversely when magnetization vectors are antiparallel, high R
Spin Valve
Simplest and most successful spintronic device
Used in HDD to read information in the form of small magnetic fields above the disk surface
Tunnel Magnetoresistance
Tunnel Magnetoresistive effect combines the two spin channels in the ferromagnetic materials and the quantum
tunnel effect
TMR junctions have resistance ratio of about 70%
MgO barrier junctions have produced 230% MR
MRAM
MRAM uses magnetic storage elements
Tunnel junctions are used to read the information stored in MRAM
MRAM
Attempts were made to control bit writing by using relatively large currents to produce fields
This proves unpractical at nanoscale level
MRAM
The spin transfer mechanism can be used to write to the magnetic memory cells
Currents are about the same as read currents, requiring much less energy
MRAM
MRAM promises:
Density of DRAM
Speed of SRAM
Non-volatility like flash
Spin Transistor
Ideal use of MRAM would utilize control of the spin channels of the current
Spin transistors would allow control of the spin current in the same manner that conventional transistors can
switch charge currents
Using arrays of these spin transistors, MRAM will combine storage, detection, logic and communication
capabilities on a single chip
This will remove the distinction between working memory and storage, combining functionality of many devices
into one
Datta Das Spin Transistor
The Datta Das Spin Transistor was first spin device proposed for metal-oxide geometry, 1989
Emitter and collector are ferromagnetic with parallel magnetizations
The gate provides magnetic field
Current is modulated by the degree of precession in electron spin
Current Research
Ferromagnetic transition temperature in excess of 100 K
Spin injection from ferromagnetic to non-magnetic semiconductors and long spin-coherence times in
semiconductors.
Ferromagnetism in Mn doped group IV semiconductors.
Room temperature ferromagnetism
Large magnetoresistance in ferromagnetic semiconductor tunnel junctions.
Future Outlook
High capacity hard drives
Magnetic RAM chips
Spin FET using quantum tunneling
Quantum computers
limitations
Controlling spin for long distances
Difficult to INJECT and MEASURE spin.
Interfernce of fields with nearest elements
Control of spin in silicon is difficult
please read
http://studentbank.in/report-spintronics--984
http://studentbank.in/report-presentatio...ics-theory
http://studentbank.in/report-spintronics
http://studentbank.in/report-relativisti...ics-theory
for getting more about seminar information of spintronics theory
