SPINTRONICS · Spintronics emerged from discoveries in the 1980s • In 1985 Johnson and Silsbee...
Transcript of SPINTRONICS · Spintronics emerged from discoveries in the 1980s • In 1985 Johnson and Silsbee...
SPINTRONICS
PRESENTING BY,
KRISHNAKUMAR.V
ROLL NO:14027176
GUIDE:ASST.PROFFTHOMAS FELIX
OUTLINE
• HISTORY
• WHAT IS SPINTRONICS?
• WHY SPINTRONICS?
• THEORY OF SPINTRONICS
• ELECTRON SPIN MANIPULATION
• GIANT MAGNETORESISTANCE
• MAGNETIC TUNNEL JUNCTION
• MRAM AND STT-MRAM
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HISTORY
• Spintronics emerged from discoveries in the 1980s
• In 1985 Johnson and Silsbee proposed observation of spin-polarized electron
injection.
• Discovery of giant magnetoresistance in 1988 by Albert Fert et al. and Peter
Grünberg et al.
• Theoretical application of spintronics begins by by Datta and Das in 1990.
• In 2017 February Massachusetts Institute of Technology introduced behavior
of Spintronics with ferromagnetic and antiferromagnetic substances..
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WHAT IS SPINTRONICS ?
• It is the study of the intrinsic spin of
the electron and its associated magnetic
moment
• It utilizes the bizarre property of spin of
electron
• Intrinsic angular property of electron is the
spin.
• It has two arbitrary orientations ±ℎ
2where h
is the plank’s constant.
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WHY SPINTRONICS?
• MOORE’S LAW
No: of Transistors doubles in every 18 months
• Complex chip design and power loss
• Information is not carried by electron charge but by it’s spin
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MOORE’S LAW• The number of transistors per square inch on integrated circuits had doubled every
year since their invention.
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ELECTRONICS VS SPINTRONICS
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THEORY OF ELECTRON SPIN
• The spin of the electron is an intrinsic angular momentum that is separate
from the angular momentum due to its orbital motion
• The magnitude of the projection of the electron's spin along an arbitrary axis
is h/2.
• Implying that the electron acts as a Fermion by the spin-statistics theorem.
• Fermion is any subatomic particle characterized by Fermi–Dirac statistics.
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SPIN–STATISTICS THEOREM
• Spin statistics theorem relates the intrinsic spin of a particle (angular
momentum not due to the orbital motion) to the particle statistics it obeys.
• The wave function of a system of identical integer-spin particles has the same
value when the positions of any two particles are swapped. Particles with wave
functions symmetric under exchange are called bosons.
• The wave function of a system of identical half-integer spin particles changes sign
when two particles are swapped. Particles with wave
functions antisymmetric under exchange are called fermions.
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• Spin of many electrons can act together to affect magnetic and electric property
of a material.
• A spintronic device requires generation or manipulation of a spin-polarized
population of electrons.
• Spin polarization can be achieved either through creating an equilibrium energy
split between spin up and spin down
• When a material is put in a large magnetic field (by Zeeman effect), the
exchange energy present in a ferromagnet forcing the system out of equilibrium.
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ZEEMEN EFFECT
• When an external magnetic field is applied, sharp spectral lines split into multiple
closely spaced lines.
• This splitting is attributed to the interaction between the magnetic field and
the magnetic dipole moment.
• The effect is due to the distortion of the electron orbitals because of the magnetic
field.
• Effect of a magnetic field is to separate the number of states into different energy
levels.
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SPIN TRANSFER TORQUE
• Spin-transfer torque is an effect in which the orientation of a magnetic layer in
a magnetic tunnel junction or spin valve can be modified using a spin-polarized
current.
• By passing a current through a thick magnetic layer ,which one can produce a
spin-polarized current.
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MANIPULATION OF ELECTRON SPIN
• Manipulation of electron spin can be achieved by
a) Quantum based electron spin manipulation
b) Mechanical Oscillator
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QUANTUM BASED ELECTRON SPIN
MANIPULATION
• Spin has to be measured before and after an
attempt to manipulate its quantum state.
• Two separate lasers are fired at the quantum
dot one tuned to excite the “up” spin state,
the other to excite the “down” state.
• These interfered with each other
destructively, preventing any fluorescence at
all and creating a so-called “dark state”.
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ELECTRON SPIN MANIPULATION
USING MECHANICAL OSCILLATOR
• Introduced by MIT Plasma Science and Fusion Center.
• It’s a new way to control electron spins without a
magnetic field.
• A transducer moving at extremely high frequency can
drive the transitions of electron spins. This
phenomenon is named as spin resonance
• An oscillator is used to "shake" the lattice to directly
flip the spins.
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SPIN POLARISATION
• Spin polarization is the degree to which the spin is aligned with a given
direction.
• This property may pertain to the spin, hence to the magnetic moment,
of conduction electrons in ferromagnetic metals.
• This property give rise to giving rise to spin-polarized currents.
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EFFECTS OF SPINTRONICS IN TECHNOLOGY
• GIANT MAGNETRORESISTANCE (GMR)
• MAGNETIC TUNNEL JUNCTION (MTJ)
• SPIN TRANSFER TORQUE
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GIANT MAGNETORESISTANCE (GMR)
• The simplest method of generating a spin polarized current is to inject the
current through a ferromagnetic material.
• The most common application of this effect is a giant magnetoresistance (GMR)
device.
• A typical GMR device consists of at least two layers
• When the two magnetization vectors
of the ferromagnetic layers are aligned, then an electrical current will flow freely
• GMR multilayer structures are also used in Magnetoresistive random-access
memory (MRAM) as cells that store one bit of information.
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HANLE EFFECT
• The Hanle effect is a reduction in the polarization of light when the atoms
emitting the light are subject to a magnetic field in a particular direction, and
when they have themselves been excited by polarized light.
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MAGNETIC TUNNEL JUNCTION
• This is a component consisting of
two ferrimagnets separated by a thin insulator.
• magnetic tunnel junctions (MTJs) have played a
central role in spintronic devices such as read heads
of hard disk drives and nonvolatile magnetoresistive
random access memories (MRAMs).
• The read-heads of modern hard disk drives work on
the basis of magnetic tunnel junctions.
• TMR, or more specifically the magnetic tunnel
junction, is also the basis of MRAM.
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MAGNETORESISTIVE RAM
• Application of Magnetic tunnel junction
• MRAM (Magnetoresistive Random Access Memory) uses electron spin to
store data.
• Memory cells are integrated on an integrated circuit chip
• MRAM is designed with potentially higher density
• MRAM uses spin-dependent tunnel junction memory cells and magnetic row
and column to write lines.
• It is currently in production by Everspin, and other companies including Global
Foundries and Samsung have announced product plans.
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• Magnetic films are separated by thin
copper layers.
• Alternating magnetic fields are with
different thickness
• A magnetic field is created when bit
current is passed.
• Magnetic fields tend to magnetize these
magnetic films
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MRAM WRITING PROCESS
• Currents are applied in both lines. Thus two magnetic fields are produced.
• Both fields are necessary to reverse the free layer magnetization
• When currents are removed returns to same configuration
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MRAM READING PROCESS
• Measurement of bit cell resistance by
applying current in the bit line.
• Comparison with a reference value
mid-way between the bit high and low
resistance values.
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SPIN TRANSFER TORQUE MAGNETIC
RAM
• Application of Magnetic tunnel junction
• STT-MRAM is an advanced type of MRAM
device.
• STT-MRAM enables higher densities, low
power consumption and reduced cost compared
to regular (so-called Toggle MRAM) devices.
• The ability to scale the STT-MRAM chips to
achieve higher densities at a lower cost.
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• In STT-MRAM the spin of the electrons
is flipped using a spin-polarized current.
• This effect is achieved in a magnetic
tunnel junction (MTJ) or a spin-valve.
• STT-MRAM devices use STT tunnel
junctions (STT-MTJ).
• A spin-polarized current is created by
passing a current though a thin magnetic
layer.
• This current is then directed into a thinner
magnetic layer which transfers the
angular momentum to the thin layer
which changes its spin.
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CONCLUSION
• Spin property of electrons are yet to be mastered
• Researchers and Scientists are taking keen interest
• Universities and electronic industries collaborating
• Span of last two decade major milestones
• It holds vast opportunities for physics and material engineering.
• Last year PTB, Germany have achieved a (2GBit/s) write cycle
• Potential of the field is colossal and continuous development is required
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REFERENCES
1) Swaroop Ghosh,Anirudh Iyengar,Seyedhamidreza Motaman,Rekha
Govindaraj,Jae-Won Jang,Jinil Chung,Jongsun Park,Xin Li,Rajiv Joshi
and Dinesh Somasekhar, “Overview of Circuits, Systems, and
Applications of Spintronics”, IEEE Journal on Emerging and Selected
topics in circuits and Systems,vol:6,no:3,September 2016.
2) Professor Liu(2017);” Spintronics with ferromagnetic and
antiferromagnetic materials” Physical Review Letters. 146603,July 2016.
3) Wolf, S. A.; Chtchelkanova, A. Y.; Treger, D. M. (2006). "Spintronics—A
retrospective and perspective". IBM Journal of Research and
Development.
4) Behin-Aein, B.; Datta, D.; Salahuddin, S.; Datta, S. (2010). "Proposal for
an all-spin logic device with built-in memory". Nature Nanotechnology.
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