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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THANK YOU

FOR

YOUR ATTENTION

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