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PAPER PRESENTATION

ON

SPINTRONICS

SUBMITTED TO:HI-TECH COLLEGE OF ENGINEERING

AND TECHNOLOGY

BYN.SIVALALITHA

ECE-1/4

B.PURNIMA

ECE-1/4

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CONTENTS

1.ABSTRACT

2.INTRODUCTION

3.METALS BASED SPINTRONIC

DEVICES

4.OTHER METALS BASED

SPINTRONICS DEVICES

4.1.APPLICATIONS

5.SEMICONDUCTOR-BASED

SPINTRONIC DEVICES

5.1.APPLICATIONS

6.SOME MORE APPLICATIONS

7.CONCLUSION

8.REFERENCES

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1. ABSTRACT:

The research field of 

Spintronics emerged 

  from experiments on

  spin-dependent electron

transport phenomena in

 solid-state devices done

in the 1980s, including 

the observation of spin-

  polarized electron

injection from a

  ferromagnetic metal to

a normal metal by  Johnson and Silsbee

(1985), and the

discovery of   giant  

magnetoresistance 

independently by  Albert  

 Fert  et al. and   Peter  

Grünberg  et al. (1988).The origins can be

traced back further to

the

 ferromagnet/supercond 

uctor tunneling  

experiments pioneered 

by Meservey and  

Tedrow, and initial 

experiments on

magnetic tunnel  

  junctions by Julliere inthe 1970s. The use of 

  semiconductors for 

  spintronics can be

traced back at least as

  far as the theoretical 

 proposal of a spin field-

effect-transistor by Datta and Das in 1990.

2. INTRODUCTION:

Spintronics (a neologism 

meaning "spin transport

electronics"), also known

as magnetoelectronics, is

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an emerging technology 

which exploits the intrinsic

spin of  electrons and its

associated magnetic moment, in addition to its

fundamental electronic

charge, in solid-state 

devices.

Electrons are spin-1/2

fermions and therefore

constitute a two-statesystem with spin "up" and

spin "down". To make a

spintronic device, the

  primary requirements are

to have a system that can

generate a current of spin

  polarized electronscomprising more of one

spin species -- up or down

-- than the other (called a

spin injector), and a

separate system that is

sensitive to the spin

  polarization of the

electrons (spin detector).Manipulation of the

electron spin during

transport between injector 

and detector (especially in

semiconductors) via spin

 precession can be

accomplished using real

external magnetic fields or effective fields caused by

spin-orbit interaction.

Spin polarization in non-

magnetic materials can be

achieved either through the

Zeeman effect in large

magnetic fields and lowtemperatures, or by non-

equilibrium methods. In

the latter case, the non-

equilibrium polarization

will decay over a timescale

called the "spin lifetime".

Spin lifetimes of  conduction electrons in

metals are relatively short

(typically less than 1

nanosecond) but in

semiconductors the

lifetimes can be very long

(microseconds at low

temperatures), especiallywhen the electrons are

isolated in local trapping

 potentials (for instance, at

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impurities, where lifetimes

can be milliseconds).

3.METALS-BASED

SPINTRONIC

DEVICES:

The simplest method of 

generating a spin-polarised

current in a metal is to passthe 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 of  ferromagnetic materials

separated by a spacer 

layer. When the two

magnetization vectors of 

the ferromagnetic layers

are aligned, the electrical

resistance will be lower (soa higher current flows at

constant voltage) than if 

the ferromagnetic layers

are anti-aligned. This

constitutes a magnetic field

sensor.

Two variants of GMR have

  been applied in devices:

(1) current-in-plane (CIP),

where the electric current

flows parallel to the layers

and (2) current-

 perpendicular-to-plane

(CPP), where the electric

current flows in a direction perpendicular to the layers.

4.OTHER METALS-

BASED

SPINTRONICS

DEVICES:

Tunnel Magnetoresistance 

where CPP transport is

achieved by using

quantum-mechanical

tunneling of electrons

through a thin insulator separating ferromagnetic

layers

The tunnel

magnetoresistance effect

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(TMR), occurs when a

current flows between two

ferromagnets separated by

a thin (about 1 nm)insulator . Then the total

resistance of the device, in

which tunneling is

responsible for  current 

flowing, changes with the

relative orientation of the

two magnetic layers. The

resistance is normallyhigher in the anti-parallel 

case. The effect is similar 

to Giant Magnetoresistance 

except that the metallic

layer is replaced by an

insulating tunnel barrier.

It was discovered in 1975

  by Michel Julliere, using

iron as the ferromagnet and

germanium as the

insulator. This experiment

was carried out at 4.2 K 

however, so it did not

attract much practicalattention.

Spin Torque Transfer ,

where a current of spin-

 polarized electrons is used

to control themagnetization direction of 

ferromagnetic electrodes in

the devices.

Spin torque transfer

writing technology is a

technology in which data is

written by re-orienting themagnetisation of a thin

magnetic layer in a tunnel

magnetoresistance (TMR)

element using a spin-

  polarised current. An

electrical current is

generally unpolarised(consisting of 50% spin-up

and 50% spin-down

electrons), a spin polarised

current is one with more

electrons of either spin. By

 passing a current through a

thick magnetic layer one

can produce a spin polarised current.

At very small device scales

it is possible that a spin

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  polarised current can

transfer its spin angular 

momentum to a small

magnetic element. Spintorque transfer magnetic

RAM (STT-MRAM) has

the advantages of lower 

  power-consumption and

  better scalability over 

conventional MRAM. Spin

torque transfer technology

has the potential to make  possible MRAM devices

combining low current

requirements and reduced

cost, however the amount

of current needed to re-

orient the magnetisation is,

at present, too high for commercial applications

and the reduction of this

current density alone is the

  basis for a lot of current

academic research in spin-

electronics.

Hynix Semiconductor andGrandis formed a

  partnership in April 2008

to explore commercial

development of STT-RAM

technology.

4.1.APPLICATIONS:

The storage density of hard 

drives is rapidly increasing

along an exponential

growth curve, in part

  because spintronics-

enabled devices like GMR and TMR sensors have

increased the sensitivity of 

the read head which

measures the magnetic

state of small magnetic

domains (bits) on the

spinning platter. The

doubling period for theareal density of  

information storage is

twelve months, much

shorter than Moore's Law,

which observes that the

number of transistors that

can cheaply beincorporated in an

integrated circuit doubles

every two years.

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MRAM, or magnetic

random access memory,

uses arrays of  TMR  or 

Spin torque transfer  devices. MRAM is

nonvolatile (unlike charge-

 based DRAM in today's

computers) so information

is stored even when power 

is turned off, potentially

  providing instant-on

computing. Motorola hasdeveloped a 256 kb

MRAM based on a single

magnetic tunnel junction

and a single transistor.

This MRAM has a

read/write cycle of under 

50 nanoseconds. Another design in development,

called Racetrack memory,

encodes information in the

direction of magnetization

 between domain walls of a

ferromagnetic metal wire.

5.

SEMICONDUCTOR-

BASED

SPINTRONIC

DEVICES: 

In early efforts, spin-  polarized electrons are

generated via optical

orientation using

circularly-polarized 

  photons at the bandgap

energy incident on

semiconductors with

appreciable spin-orbit

interaction (like GaAs and

ZnSe). Although electrical

spin injection can be

achieved in metallic

systems by simply passing

a current through a

ferromagnet, the largeimpedance mismatch

  between ferromagnetic

metals and semiconductors

  prevented efficient

injection across metal-

semiconductor interfaces.

A solution to this problemis to use ferromagnetic

semiconductor sources

(like manganese-doped

gallium arsenide

GaMnAs), increasing the

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interface resistance with a

tunnel barrier, or using

hot-electron injection.

Spin detection in

semiconductors is another 

challenge, which has been

met with the following

techniques:

• Faraday/Kerr rotation

of transmitted/reflected

 photons

• Circular polarization

analysis of  

electroluminescence

•   Nonlocal spin valve

(adapted from

Johnson and Silsbee'swork with metals)

• Ballistic spin filtering

The latter technique was

used to overcome the lack 

of spin-orbit interaction

and materials issues toachieve spin transport in

Silicon, the most important

semiconductor for  

electronics.

Because external magnetic

fields (and stray fields

from magnetic contacts)

can cause large Hall effects and magnetoresistance in

semiconductors (which

mimic spin-valve effects),

the only conclusive

evidence of spin transport

in semiconductors is

demonstration of spin

 precession and dephasing in a magnetic field non-

colinear to the injected

spin orientation. This is

called the Hanle effect.

5.1.APPLICATIONS:

Advantages of  

semiconductor-based

spintronics applications are

  potentially lower power 

use and a smaller footprint

than electrical devices usedfor information processing.

Also, applications such as

semiconductor lasers using

spin-polarized electrical

injection have shown

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threshold current reduction

and controllable circularly

  polarized coherent light

output. Future applicationsmay include a spin-based

transistor  having

advantages over  MOSFET 

devices such as steeper 

sub-threshold slope.

6.SOME MORE

APPLICATIONS:

• Spin pumping is a

method of generating

a spin current, the

spintronic analog of a

 battery inconventional

electronics.

• spin transfer is the

 phenomenon in which

the spin angular  

momentum of the

charge carriers (usually electrons) get

transferred from one

location to another.

This phenomenon is

responsible for  

several important and

observable physical

effects.

•

Spinplasmonics is afield of  

nanotechnology 

combining spintronics 

and plasmonics

In a spinplasmonic device,

light waves couple to

electron spin states in ametallic structure.

Spinplasmonic devices

  potentially have the

advantages of high speed,

miniaturization, low power 

consumption, anUnlike

semiconductor-baseddevices, smaller  

spinplasmonics devices are

expected to be more

efficient in transporting the

spin-polarized electron

current.d multifunctional

• ADVANTAGES:The various advantages

of spintronics are as

follows:

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-spintronics does not

require unique and

specialised

semiconductors,therefore it can be

implemented or worked

with common metals,

such as copper,

aluminium and silver.

- spintronics devices

wouldwould consume

less power compareed toconventional electronics,

  because the energy

needed to change spin is

a easy compared to

energy needed to push

charge around.

- since spins don’tchange when power is

turned turned off, the

memory remains non-

volatile.

• DISADVANTAG

ES:If an attempt were

made to make

magnetic RAM

capable of retaining

important data, it

would be very

difficult task to

achieve. The primary

reason beinginterference of fields

with nearest element.

  suppose the indvidual

memory elements are

adressed by flipping

their spins up or down to

yield the zeros and ones

of binary computer logic. In that case, the

common strategy of 

running current pulses

through wires to induce

magnetic fields to rotate

the elements is flawed.

This may happen because the fringe fields

that are generated may

interfere with

neighbouring elements.

7.CONCLUSION:

Spintronics still remains

to be far away from

 being the best friend and

source of electronic

industry. But in order to

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convert it into reality,

many major  

manufactures have

already startedinvestigating magnetic

RAM technology, and

they are keeping their 

eyes on magnetic CPUs

for the furure. As the

development in

spintronics is bound to

  bring a new era of  semiconductor 

spintronics that could

 potentially transform the

microelectronics

industry. But more

impotantly,with the

magnetic storageindustry currently

accounting for billions

range when power is

turned off, the memory

remains non-volatile.

8.REFERENCES:

1. IBM RD 50-1 |

Spintronics—A

retrospective and

 perspective 

2. Physics Profile: "Stu

Wolf: True D!Hollywood Story" 

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4. Phys. Rev. Lett. 61

(1988): M. N.

Baibich, J. M. Broto,

A. Fert, F. NguyenVan Dau, F. Petroff,

P. Eitenne, G.

Creuzet, A.

Friederich, and J.

Chazelas - Giant

Magnetoresistanc... 

5. http://prola.aps.org/pdf/PRB/v39/i7/p4828_ 

1 

6. PII: 0370-

1573(94)90105-8 

7. http://www.sciencedir 

ect.com/science/articl

e/B6TVM-46R3N46-10D/2/90703cfc684b0

679356dce9a76b2e94

2 

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9. http://www.sigmaaldr 

ich.com/materials-

science/alternative-

energy-materials/magnetic-

materials/tutorial/spin

tronics.html 

10. Phys. Rev. B 62

(2000): B. T. Jonker,

Y. D. Park, B. R.

Bennett, H. D.

Cheong, G.Kioseoglou, and A.

Petrou - Robust

electrical spin

injection 

11. Cookies Required 

12. Phys. Rev. Lett. 90

(2003): X. Jiang, R.Wang, S. van Dijken,

R. Shelby, R.

Macfarlane, G. S.

Solomon, J. Harris,

and S. S. Parkin -

Optical Detection of 

Hot-Electron 13. Phys. Rev. Lett. 80

(1998): J. M.

Kikkawa and D. D.

Awschalom -

Resonant Spin

Amplification in 

14. Polarized optical

emission due to decayor recombination of 

spin-polarized

injected carriers - US

Patent 5874749 

15. Electrical detection of 

spin transport in

lateral ferromagnet-

semiconductor devices : Abstract :

 Nature Physics