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1. Heaven’s Light is Our Guide
Rajshahi University of Engineering & Technology
Department of Physics
Presented by
Md. Faruk Hossain
Master of Philosophy (M. Phil.) Student
Department of Physics
Rajshahi University of Engineering & Technology
Rajshahi-6204, Bangladesh
Spintronics

2. Outline
 A Brief History
 Why Spintronics?
 What is Spintronics?
 Principle
 The Story Behind
 Advantages of Spin
 Giant Magnetoresistance
 GMR Structure
 Tunnel Magnetoresistance
 Magnetic Tunnel Junction
 Spintronics Devices
 MRAM, FET
 Conventional Electronics
vs Spintronics
 Where are we?
 Advantages
 Limitations
 Conclusion
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3. A Brief History
1920s: Spin concept
1988: Discovery of Giant Magnetoresistance
1991: Invention of Spin Valve by IBM
1994: Magnetic Tunnel Junction with large Magneto
resistance ratio.
1997: First GMR Hard disk Head introduced by IBM
2005: Commercialization of MTJ Read head
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4. Why Spintronics?
 Moore’s Law:
No. of Transistor doubles in every 18 months.
 Complexity:
Complex Chip Design & Power Loss
 Motivation:
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Spintronics –Information is carried not by electron
charge but by it’s spin. Spintronics could be more
revolutionary than any other nanotechnology.
The main purpose of development of spintronics and it’s
devices is to make memory more compact than today

5. What is Spintronics?
 Spintronics is the branch of science which deals with
spin dependent properties of an electron instead of its
charge dependent properties.
 It refers to the study of the role played by the electron
spin in solid state physics. Spin of electron can be
either -1/2 or +1/2.
 It promises new logic devices which enhances
functionality, high speed and reduced power
consumption.
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6. Principle
• Spintronics is based on the spin of electrons rather than its charge.
• Every electron exist in one of the 2 states-spin up and spin-down,
with spins either positive half or negative half.
• The two possible spin states represent ‘0’ and ‘1’ in logical
operations.
• The orientation of N-S axis depends on the particle’s axis of spin.
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7. Principle
• In ordinary materials, the up magnetic moments cancel the down
magnetic moment so no surplus moment piles up.
• Ferro-magnetic materials like iron, cobalt and nickel is needed for
designing of spin electronic devices. These have tiny regions called
domains in which an excess of electrons have spins with axis
pointing either up or down.
• The domains are randomly scattered and evenly divided between
majority-up and majority down.
• But, an externally applied magnetic field will line up the domains in
the direction of the field. This results in permanent magnet.
• The frequency and direction of rotation depends on the strength of
magnetic field and characteristics of the material.
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8. The Story Behind
• Spin Magnetism
• Ordinary materials
• Ferromagnetic materials
External magnetic field
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9. The Story Behind
 Ferromagnetic Materials’ Role
• Spin Polarizer
• Spin Filter
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10. Advantages of Spin
• Information is stored into spin as one of two possible
orientations
• Spin lifetime is relatively long, on the order of
nanoseconds
• Spin currents can be manipulated
• Spin devices may combine logic and storage functionality
eliminating the need for separate components
• Magnetic storage is nonvolatile
• Binary spin polarization offers the possibility of
applications as qubits in quantum computers
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11. Advantages of Spin
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12. Giant Magnetoresistance (GMR)
• In 1988, GMR discovery by Albert Fert (France) and Peter
Grünberg (Germany) (Nobel prize 2007) is accepted as
birth of spintronics
• A Giant Magneto Resistive device is made of at least two
ferromagnetic layers separated by a spacer layer
• When the magnetization of the two outside layers is
aligned, lowest resistance, conversely when magnetization
vectors are antiparallel, high R
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13. The electrical resistance depends on
the relative magnetic alignment of the ferromagnetic layers
19% for trilayers @RT
80% for multilayers @ RT
Ferromagnet
Metal
Ferromagnet
Electrical
resistance: RP < RAP
GMR 
RAP  RP
RP








R
R
R
R
R
R
GMR para
2
)
(
4
1
/
Giant Magnetoresistance (GMR)
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14. Spin-dependent scattering
1) Both electron spins
experience small resistance
in one layer and large
resistance in the other.
2) Up-spin electrons experience
small resistance, down-spin
electrons experience large
resistance.
)
(
2
1



 R
R
Rantpara






R
R
R
R
Rpara
2
Giant Magnetoresistance (GMR)
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15. GMR Structure
1.5% drop in resistance
reported
Nearly 50% drop in resistance
observed
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16. Tunnel Magnetoresistance (TMR)
• Tunnel Magnetoresistive (TMR) effect combines the two
spin channels in the ferromagnetic materials and the
quantum tunnel effect
• Tunnel magnetoresistance(TMR) is a magnetoresistive
effect that occurs in a magnetic tunnel junction(MTJ),
which is a component consisting of two ferromagnets
separated by a thin insulator.
• TMR junctions have resistance
ratio of about 70%
• MgO barrier junctions have
produced 230% MR
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17. Two conducting electrodes are separated by a thin
dielectric layer with a thickness ranging from a few
angstroms to a few nanometers.
The electron tunneling phenomenon arises from the wave
nature of the electrons.
Magnetic Tunnel Junction
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18. Magnetic Tunnel Junction
• MTJ
• Two layers of
ferromagnetic material
separated by an extremely
thin non-conductive barrier.
• Parallel -> Low resistance
• Anti-parallel -> High
resistance
Fixed
Layer
Free
Layer
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19. Spintronics Devices
• Metal-based spintronics devices
• Ready for commercial product
(successfully fabricated, good yield,
less process variation)
• Used as memory devices in MRAM
• Strong candidate for universal memory
• logic design
• Semiconductor-based spintronics
devices
• Build on semiconductor materials
• Extra degree of freedom
MTJ
Spin-FET
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20. MRAM
• MRAM uses magnetic storage elements instead of electric
used in conventional RAM
• Tunnel junctions are used to read the information stored in
Magnetoresistive Random Access Memory, typically a ‘0’
for zero point magnetization state and ‘1’ for antiparallel
state
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MRAM MRAM Chip

21. 21
FET
At zero gate voltage, electron preserves spin state in transport
channel (a) it enables current flow from source to drain.
of ferromagnetic layer
(b) this offers high
resistance to flow of
current. Therefore,
electron scattering
occurs at drain and no
current flow from
source to drain.
With applied gate voltage, electrons change their spin state
from parallel to anti parallel to the direction of magnetization
Dutta-Das field effect transistor

22. Concatenation meaning: spin electronics
 Conventional electronics: rely on charge property of electrons for application
 Spintronics: rely on either solely on the spin or spin plus charge for application
Conventional Electronics vs Spintronics
Electronic Devices Spintronic devices
1. Based on properties of charge of the
electron
1. Based on intrinsic property spin of
electron
2. Classical property 2. Quantum property
3. Controlled by an external electric
field in modern electronics
3. Controlled by external magnetic
field
4. Materials: conductors and
semiconductors
4. Materials: ferromagnetic materials
5. Based on the number of charges and
their energy
5. Two basic spin states; spin-up and
spin-down
6. Speed is limited and power
dissipation is high
6. Based on direction of spin and spin
coupling, high speed
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23. 23
Where are we?
Till now, spintronics is realized only in all-metallic systems for
applications in magnetic field sensing and non-volatile storage.
Metal-based spintronics devices
Semiconductor-based spintronics devices
We are here
Magnetic filed sensing
Non-volatile storage
Logic design?
Logic design
Quantum computation
….
Quantum dot storage

24. 24
Areal Density progression in HDDs
Where are we?

25. • Non-volatile memory
• Performance improves with smaller devices
• Low power consumption
• Spintronics does not require unique and specialised
semiconductors
• Dissipationless 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
• Promises a greater integration between the logic and
storage devices
Advantages
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26. Existing metal-based devices do not amplify signals,
whereas semiconductor based spintronic devices could in
principle provide amplification and serve, in general, as
multi-functional devices.
All the available ferromagnetic semiconductor materials
that can be used as spin injectors preserve their properties
only far below room temperature, because their Curie
temperatures (TC) are low.
Controlling spin for long distances.
Difficult to inject spin-polarized currents, or spin currents,
into a semiconductor.
Limitations
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27. 27
Conclusion
 Interest in spintronics arises, in part, from the looming
problem of exhausting the fundamental physical limits of
conventional electronics.
 The spin of the electron has attracted renewed interest
because it promises a wide variety of new devices that
combine logic, storage and sensor applications.
 Moreover, these "spintronic" devices might lead to
quantum computers and quantum communication based on
electronic solid-state devices, thus changing the
perspective of information technology in the 21st century.

28. References
1. Parkin S.S.P. Phys. Rev. Lett. 1991; 67: 3958
2. Pierce D.T. et al. Phys. Rev. B. 1994 ;49: 14564
3. Peplov M. Nature. 2015; 522: 268.
4. Day C. Physics Today. 2007; 60(12): 12.
5. Tsymbal EY, Pettifor DG. In Solid state physics. 2001; 56: 113-
237.
6. Binasch G, Grünberg P, Saurenbach F, Zinn W. Physical review B.
1989; 39(7): 4828.
7. Baibich MN, Broto JM, Fert A, Van Dau FN, Petroff F, Etienne P,
Creuzet G, Friederich A, Chazelas J. Physical review letters. 1988
; 61(21): 2472.
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29. THANK YOU VERY MUCH
FOR YOUR
KIND ATTENTION
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