A

Seminar Report on

“Spintronics”

submitted for partial fulfilment of award of

BACHELORS OF TECHNOLOGY

degree

in

Electronics and Communication Engineering

by

Shishu Pal

(Roll No.1213331191)

Submitted to

Ms. Kanika Jindal (AP, ECE Deptt.)

Ms. Gitanjali Anand (AP, ECE Deptt.)

Mr.Devendra Pratap(AP, ECE Deptt.)

NOIDA INSTITUTE OF ENGINEERING & TECHNOLOGY

GREATER NOIDA

March, 2015

DECLARATION

I hereby declare that the seminar report which is being presented in the entitled “Spintronics,”

in partial fulfillment of the requirements for the award of degree of Bachelors of Technology in

Electronics and Communication Engineering in the Department of Electronics and

Communication Engineering from Noida Institute of Engineering and Technology, Greater

Noida, is an authentic record of my own carried out under the supervision of Mr. Devendra

Pratap Singh and Ms. Kanika Jindal, Assistant Professor, Department of ECE.

Date:17/03/2015 SHISHU PAL

Roll. No. 1213331191

CERTIFICATE

Certified that seminar work entitled “Spintronics ” is a bonafide work carried out in the sixth

semester by “Shishu Pal” in partial fulfilment for the award of Bachelor of Technology in

Electronics and Communication Engineering from Uttar Pradesh Technical University during

the academic year 2013-2014 who carried out the seminar work.

Date: 17/03/2015 Ms.Kanika Jindal

Ms. Gitanjali Anand

Mr. Devendra Pratap Singh

ACKNOWLEDGEMENT

It gives me great pleasure to present my seminar report on “Spintronics”. No work , however

big or small, has ever been done without the contributions of others.

It would be a great pleasure to write a few words, which would although not suffice as the

acknowledgement of this long cherished effort, but in the absence of which this report would

necessarily be incomplete. So these words of acknowledgement come as a small gesture of

gratitude towards all those people, without whom the successful completion of this project would

not have been possible.

I would like to express deep gratitude towards Ms. Gitanjali Anand (Associate Professor of

ECE Dept.) & Ms. Kanika Jindal (Associate Professor of ECE Dept.) who gave me their

valuable suggestions, motivation and the direction to proceed at every stage. They are like a

beam of light for us. Their kind guidance showed us the path of life and is unforgettable. They

extended towards their valuable guidance, indispensable help and inspiration at times in

appreciation I offer them my sincere gratitude.

Last but not least we would like to thank the Department of Electronics and communication

Engineering, NIET, Gr. Noida for providing me with the facilities to lab, and all staff members

of ECE Dept., it would have been impossible for me to complete my project without their

valuable guidance & prompt cooperation.

I have tried my level best to make this seminar report error free ,but I regret for errors, if any.

ABSTRACT

Spintronics is an emergent technology that exploits the quantum propensity of the electrons to

spin as well as making use of their charge state. The spin itself is manifested as a detectable

weak magnetic energy state characterised as ―spin up‖ or ―spin down‖.

Conventional electronic devices rely on the transport of electrical charge carriers – electrons – in

a semiconductor such as silicon. Now, however, device engineers and physicists are inevitably

faced the looming presence of quantum mechanics and are trying to exploit the spin of the

electron rather than its charge. Devices that rely on the electron‘s spin to perform their functions

form the foundations of spintronics (short for spin-based electronics), also known as magneto

electronics. Spintronics devices are smaller than 100 nanometre in size, more versatile and more

robust than those making up silicon chips and circuit elements. The potential market is worth

hundreds of billions of dollar a year.

Spintronics burst on the scene in 1988 when French and German physicists discovered a very

powerful effect called Giant Magneto resistance (GMR). It results from subtle electron-spin

effects in ultra thin multilayer of magnetic materials, which cause huge changes in their electrical

resistance when a magnetic field is applied. This resulted in the first spintronics device in the

form of the spin valve. The incorporation of GMR materials into read heads allowed the storage

capacity of a hard disk to increase from one to 20 gigabits. In 1997, IBM launched GMR read

heads, into a market worth around a billion dollars a year.

The field of spintronics is relatively young and it is difficult to predict how it will evolve. New

physics is still being discovered and new materials being developed, such as magnetic

semiconductors and exotic oxides that manifest an even more extreme effect called Colossal

Magneto resistance.

TABLE OF CONTENTS

CHAPTER NO. TITLE PAGE NO.

DECLARATION ii

CERTIFICATE iii

ACKNOWLEDGEMENTS iv

ABSTRACT v

TABLE OF CONTENTS vi

LIST OF FIGURES vii

1. INTRODUCTION 01

2. MOTIVATION 02

3. TECHNOLOGY DESCRIPTION 03

3.1Gaint Magneto resistance 04

3.2 Construction of GMR 05

3.3 Spin Valve GMR 07

3.4 Memory Chips 08

3.5 GMR Sensor 09

3.6 Spintronics Devices 09

MRAM 10

Spin Transistors 11

Quantum Computer 14

Spintronics Scanner 16

3.7 Advantages / Disadvantages 19

3.8 Real Time Applications 20

4. CONCLUTION AND FUTURE SCOPE 22

5. Reference 25

LIST OF FIGURES

S.NO. TITLE PAGE NO.

1. Electron spinning 02

2. Magnetic Orientation of electrons 03

.

3. A GMR Device 04

4. Construction of GMR 06

5. GMR based Spin Valves for read head In hard drives 07

6. GMR Sensor 09

7. MRAM 11

8. Spin based transistor 12

9. Spin polarized field effect Transistor 12

INTRODUCTION

Conventional electronic devices rely on the transport of electrical charge carriers –electrons in a

semiconductor such as silicon. Now, however, physicists are trying to exploit the ‗spin‘ of the

electron rather than its charge to create a remarkable new generation of spintronics‘ devices

which will be smaller, more versatile and more robust than those currently making up silicon

chips and circuit elements.

Imagine a data storage device of the size of an atom working at a speed of light. Imagine a

computer memory thousands of times denser and faster than today‘s memories and also imagine

a scanner technique which can detect cancer cells even though they are less in number. The

above-mentioned things can be made possible with the help of an exploding science –

―Spintronics‖.

Spintronics is a technology which deals with spin dependent properties of an electron instead of

or in addition to its charge dependent properties. Conventional electronics devices rely on the

transport of electric charge carries-electrons. But there is other dimensions of an electron other

than its charge and mass i.e. spin. This dimension can be exploited to create a remarkable

generation of spintronics devices. It is believed that in the near future spintronics could be more

revolutionary than any other technology.

As there is rapid progress in the miniaturization of semiconductor electronic devices leads to a

chip features smaller than 100 nanometers in size, device engineers and physicists are inevitable

faced with a looming presence of a quantum property of an electron known as spin, which is

closely related to magnetism. Devices that rely on an electron spin to perform their functions

form the foundations of spintronics.

Information-processing technology has thus far relied on purely charge based devices ranging

from the now quantum, vacuum tube today‘s million transistor microchips. Those conventional

electronic devices move electronic charges around, ignoring the spin that tags along that side on

each electron.

MOTIVATION

The basic principle involved is the usage of spin of the electron in addition to mass and charge of

electron. Electrons like all fundamental particles have a property called spin which can be

orientated in one direction or the other – called ‗spin-up‘ or ‗spin-down‘ –like a top spinning

anticlockwise or clockwise. Spin is the root cause of magnetism and is a kind of intrinsic angular

momentum that a particle cannot gain or lose. The two possible spin states naturally represent

‘0‘and ‘1‘in logical operations. Spin is the characteristics that makes the electron a tiny magnet

complete with north and south poles .The orientation of the tiny magnet ‘s north-south poles

depends on the particle‘s axis of spin.

Fundamentals of spin:

1.In addition to their mass, electrons have an intrinsic quantity of angular momentum called spin,

almost of if they were tiny spinning balls.

2.Associated with the spin is magnetic field like that of a tiny bar magnet lined up with the spin

axis.

Fig.1. Electron spinning

2. Scientists represent the spin with a vector. For a sphere spinning ―west to east‖, the vector

points ― north‖ or ―up‖. It points ―south‖ or ―down‖ for the spin from ―east to west‖.

4. In a magnetic field, electrons with ―spin up‖ and ―spin down‖ have different energies.

5. In an ordinary electronic circuit the spins are oriented at random and have no effect on current

flow.

6. Spintronics devices create spin-polarized currents and use the spin to control current flow.

TECHNOLOGY DESCRIPTION

The use of the spintronics requires that the materials used to fabricate the spin devices should

possess the following requirements to be satisfied by the material:

Efficient electrical injection of spin – polarized carriers.

Efficient transmission during transport of carriers through semiconductor.

Capability to detect or collect spin – polarized current.

SPIN MATERIALS:-

The basic materials used in spin devices for manipulation of spin of electrons are the

ferromagnetic which have the capability to change the spin polarization on application of

magnetic fields.The spin materials can be classified into two groups:

Ferromagnetic Semiconductors

Half-Magnetic ferromagnets

Ferromagnetic Semiconductors

These are the materials with complete control over the spin electron. The main advantages of

these types of materials are:

Combined semiconducting and magnetic properties for multiple functionalities

Easy growth of ferromagnetic-semiconductor nanostructures.

Easy spin injection

Half-Magnetic ferromagnets

As name suggests the half – magnetic ferromagnets doesn’t have full control over spin of the

electrons. The spin materials can be obtained as: - Substitution of V, Cr and Mn into GaAs,

InAs,GaSb,GaP and InP.

Fig 2. Magnetic Orientation of electrons

Giant Magneto Resistance

Electrons like all fundamental particles have a property called spin which can be orientated in

one direction or the other – called „spin-up‟ or „spin-down‟ – like a top spinning anticlockwise

or clockwise. When electron spins are aligned (i.e. all spin-up or all spin-down) they create a

large-scale net magnetic moment as seen in magnetic materials like iron and cobalt. Magnetism

is an intrinsic physical property associated with the spins of electrons in a material.

Magnetism is already exploited in recording devices such as computer hard disks Data are

recorded and stored as tiny areas of magnetised iron or chromium oxide. To access the

information, a read head detects the minute changes in magnetic field as the disk spins

underneath it. This induces corresponding changes in the head‟s electrical resistance – an effect

called magneto resistance.

Spintronics burst on the scene in 1988 when French and German physicists discovered a much

more powerful effect called „giant magneto resistance‟ (GMR). It results from subtle electron-

spin effects in ultra-thin „multilayer’s‟ of magnetic materials, which cause huge changes in their

electrical resistance when a magnetic field is applied. GMR is 200 times stronger than ordinary

magneto resistance. IBM soon realised that read heads incorporating GMR materials would be

able to sense much smaller magnetic fields, allowing the storage capacity of a hard disk to

increase from 1 to 20 gigabits. In 1997 IBM launched GMR read heads, into a market worth

about a billion dollars a year.

The basic GMR device consists of a three-layer sandwich of a magnetic metal such as cobalt

with a nonmagnetic metal filling such as silver (see diagram).

Fig 3. A GMR Device

A current passes through the layers consisting of spin-up and spin-down electrons. Those

oriented in the same direction as the electron spins in a magnetic layer pass through quite easily

while those oriented in the opposite direction are scattered.

If orientation of one of the magnetic layers can easily be changed by the presence of a magnetic

field then the device will act as a filter, or „spin valve‟, letting through more electrons when the

spin orientations in the two layers are the same and fewer when orientations are oppositely

aligned. The electrical resistance of the device can therefore be changed dramatically.

The magneto resistant devices can sense the changes in the magnetic field only to a small extent,

which is appropriate to the existing memory devices. When we reduce the size and increase data

storage density, we reduce the bits, so our sensor also has to be small and maintain very, very

high sensitivity. The thought gave rise to the powerful effect called ―Giant Magneto resistance

(GMR).GMR is a quantum mechanical magneto resistance effect observed in thin film structures

composed of alternating ferromagnetic and non magnetic layers. The 2007 Nobel Prize in

physics was awarded to Albert Fret and Peter Gruenberg for the discovery of GMR.

Giant magneto resistance (GMR) came into picture in 1988, which lead the rise of spintronics. It

results from subtle electron-spin effects in ultra-thin ‗multilayer‘ of magnetic materials, which

cause huge changes in their electrical resistance when a magnetic field is applied. GMR is 200

times stronger than ordinary magneto resistance. It was soon realized that read heads

incorporating GMR materials would be able to sense much smaller magnetic fields, allowing the

storage capacity of a hard disk to increase from 1 to 20 gigabits.

Construction of GMR

The basic GMR device consists of a three-layer sandwich of a magnetic metal such as cobalt

with a nonmagnetic metal filling such as silver. Current passes through the layers consisting of

spin-up and spin-down electrons. Those oriented in the same direction as the electron spins in a

magnetic layer pass through quite easily while those oriented in the opposite direction are

scattered. If the orientation of one of the magnetic layers can easily be changed by the presence

of a magnetic field then the device will act as a filter, or ‗spin valve‘, letting through more

electrons when the spin orientations in the two layers are the same and fewer when orientations

are oppositely aligned. The electrical resistance of the device can therefore be changed

dramatically. In an ordinary electric current, the spin points at random and plays no role in

determining the resistance of a wire or the amplification of a transistor circuit. Spintronics

devices in contrast, rely on differences in the transport of ―spin up‖ and ―spin down‖ electrons.

Figure 4: Construction of GMR

A ferromagnet can even affect the flow of a current in a nearby nonmagnetic metal. For example,

in the present-day read heads in computer hard drives, wherein a layer of a nonmagnetic metal is

sandwiched between two ferromagnetic metallic layers, the magnetization of the first layer is

fixed, or pinned, but the second ferromagnetic layer is not. As the read head travels along a track

of data on a computer disk, the small magnetic fields of the recorded 1‘s and 0`s change the

second layer‘s magnetization back and forth parallel or antiparallel to the magnetization of the

pinned layer. In the parallel case, only electrons that are oriented in the favored direction flow

through the conductor easily. In the antiparallel case, all electrons are impeded. The resulting

changes in the current allow GMR read heads to detect weaker fields than their predecessors; so

that data can be stored using more tightly packaged magnetized spots on a disk.

GMR has triggered the rise of a new field of electronics called spintronics which has been used

extensively in the read heads of modern hard drives and magnetic sensors. A hard disk storing

binary information can use the difference in resistance between parallel and antiparallel layer

alignments as a method of storing 1s and 0s.

A high GMR is preferred for optimal data storage density. Current perpendicular-to-plane (CPP)

Spin valve GMR currently yields the highest GMR. Research continues with older current-in-

plane configuration and in the tunnelling magnetoresistance (TMR) spin valves which enable

disk drive densities exceeding 1 Terabyte per squar inch.

Hard disk drive manufacturers have investigated magnetic sensors based on the colossal magneto

resistance effect (CMR) and the giant planar Hall effect. In the lab, such sensors have

demonstrated sensitivity which is orders of magnitude stronger than GMR. In principle, this

could lead to orders of magnitude improvement in hard drive data density.

As of 2003, only GMR has been exploited in commercial disk read-and-write heads because

researchers have not demonstrated the CMR or giant planar hall effects at temperatures above

150K.

Magneto coupler is a device that uses giant magneto resistance (GMR) to couple two electrical

circuits galvanic isolated and works from AC down to DC.

Vibration measurement in MEMS systems.

Detecting DNA or protein binding to capture molecules in a surface layer by measuring the stray

field from super paramagnetic label particles.

Spin Valve GMR

If the orientation of one of the magnetic layers can easily be changed by the presence of a

magnetic field then the device will act as a filter, or ‗spin valve‘, letting through more electrons

when the spin orientations in the two layers are the same and fewer when orientations are

oppositely aligned. The electrical resistance of the device can therefore be changed dramatically.

Fig 5. Standard geometry for GMR based Spin Valve

An electron passing through the spin-valve will be scattered more if the spin of the electrons

opposite to the direction of the magnetisation in the Field.

Memory Chips

Physicists have been quick to see the further possibilities of spin valves. Not only are they highly

sensitive magnetic sensors , they can also be made to act as switches by flipping the

magnetisation in one of the layers. This allows information to be stored as 0s and 1s

(magnetisations of the layers parallel or antiparallel) as in a conventional transistor memory

device. An obvious application is a magnetic version of a random access memory (RAM) device

of the kind used in your computer. The advantage of magnetic random access memory (MRAM)

is that it is „non-volatile‟ – information isn‟t lost when the system is switched off. MRAM

devices would be smaller, faster, cheaper, use less power and would be much more robust in

extreme conditions such as high temperature, or highlevel radiation or interference. The US

electronics company Honeywell has already shown that arrays of linked MRAMS could be made

to work. The potential market for MRAMS is worth 100 billion dollars annually.

Over the past three years or so, researchers around the world have been working hard on a whole

range of MRAM devices. A particularly promising device is the magnetic tunnel junction, which

has two magnetic layers separated by an insulating metal-oxide layer. Electrons can tunnel

through from one layer to the other only when magnetisations of the layers point in the same

direction, otherwise the resistance is high – in fact, 1000 times higher than in the standard spin

valve.

Even more interesting are devices that combine the magnetic layers with semiconductors like

silicon. The advantage is that silicon is still the favourite material of the electronics industry and

likely to remain so. Such hybrid devices could be made to behave more like conventional

transistors. They could be used as non-volatile logic elements which could be reprogrammed

using software during actual processing to create an entirely new type of very fast computing.

The field of spintronics is extremely young and it’s difficult to predict how it will evolve. New

physics is still being discovered and new materials being developed, such as magnetic

semiconductors, and exotic oxides that manifest an even more extreme effect called colossal

magneto resistance. What is certain is that the time-span from a breakthrough in fundamental

physics to first commercial exploitation has been less than 10 years. The business opportunities

for spintronics are still wide open. European research collaborations, some involving the Us,

have a strong lead in developing the underlying physics and technology for this lucrative

fledgling industry.

GMR SENSORS

GMR sensors are already being developed in UK universities. They have a wide range of

applications and the market is worth 8 billion dollars a year. Applications include:

• Fast accurate position and motion sensing of mechanical components in precision engineering

and in robotics

• All kinds of automotive sensors for fuel handling systems, electronic engine control, antiskid

systems, speed control and navigation

• Missile guidance

• Position and motion sensing in computer video games

• Key-hole surgery and post-operative care

Figure 6: GMR Sensor

The magnetic property of a battery changes with SoC. A Sensor reads the change when exposed

to a magnetic field.

SPINTRONICS DEVICES

Spintronic devices are those devices which use the Spintronics technology. Spintronics-devices

combine the advantages of magnetic materials and semiconductors. They are expected to be non-

volatile, versatile, fast and capable of simultaneous data storage and processing, while at the

same time consuming less energy. Spintronics-devices are playing an increasingly significant

role in high-density data storage, microelectronics, sensors, quantum computing and bio-medical

applications, etc.

Electronic Devices v/s Spintronics Devices

Electronic Devices Spintronics devices

1. Based on properties of charge of the 1. Based on intrinsic property spin of electron.

electron

2. Classical property 2. Quantum property

4. Materials: conductors and semiconductors 4. Materials: ferromagnetic materials

5. Based on the number of charges and their 5. Two basic spin states; spin-up and spin-

energy down.

6. Speed is limited and power dissipation is 6. Based on direction of spin and spin and spin

high. coupling, high speed.

Some of the Spintronic devices are:

Magnetoresistive Random Access Memory(MRAM)

Spin Transistor

Quantum Computer

Spintronic Scanner

MRAM (Magneto resistive Random Access Memory)

An important spintronics device, which is supposed to be one of the first spintronics devices that

have been invented, is MRAM.

Unlike conventional random-access, MRAMs do not lose stored information once the power is

turned off...A MRAM computer uses power, the four page e mail will be right there for you.

Today pc use SRAM and DRAM both known as volatile memory. They can store information

only if we have power. DRAM is a series of capacitors, a charged capacitor represents 1 where

as an uncharged capacitor represents 0. To retain 1 you must constantly feed the capacitor with

power because the charge you put into the capacitor is constantly leaking out.

Fig 8. 256 K MRAM

MRAM is based on integration of magnetic tunnel junction (MJT). Magnetic tunnel junction is a

three-layered device having a thin insulating layer between two metallic ferromagnets. Current

flows through the device by the process of quantum tunneling; a small number of electrons

manage to jump through the barrier even though they are forbidden to be in the insulator. The

tunneling current is obstructed when the two ferromagnetic layers have opposite orientations and

is allowed when their orientations are the same.

MRAM stores bits as magnetic polarities rather than electric charges. When a big polarity points

in one direction it holds1, when its polarity points in other direction it holds 0. These bits need

electricity to change the direction but not to maintain them. MRAM is non volatile so, when you

turn your computer off all the bits retain their 1`s and 0`s.

SPIN TRANSISTORS

Traditional transistors use on-and-off charge currents to create bits- the binary zeroes and ones of

computer information. “Quantum spin field effect” transistor will use up-and-down spin states to

generate the same binary data. One can think of electron spin as an arrow; it can point upward or

downward; “spinup and spin-down can be thought of as a digital system, representing the binary

0 and 1. The quantum transistor employs also called “spin-flip” mechanism to flip an up-spin to

a downspin, or change the binary state from 0 to 1.

One proposed design of a spin FET (spintronic field-effect transistor) has a source and a drain,

separated by a narrow semi conducting channel, the same as in a conventional FET. In the spin

FET, both the source and the drain are ferromagnetic. The source sends spin-polarized electrons

in to the channel, and this spin current flow easily if it reaches the drain unaltered (top).

Fig 9: Spin Based Transistor

A voltage applied to the gate electrode produces an electric field in the channel, which causes the

spins of fastmoving electrons to process, or rotate (bottom). The drain impedes the spin

currentaccording to how far the spins have been rotated. Flipping spins in this way takes much

less energy and is much faster than the conventional FET process of pushing charges out of the

channel with a larger electric filed.

In these devices a non magnetic layer which is used for transmitting and controlling the spin

polarized electrons from source to drain plays a crucial role. For functioning of this device first

the spins have to be injected from source into this non-magnetic layer and then transmitted to the

collector. These non-magnetic layers are also called as semimetals, because they have very larger

spin diffusion lengths.The injected spins which are transmitted through this layer start processing

as illustrated in Figure before they reach the collector due to the spin-orbit coupling effect.

Fig.10 Spin polarized field effect transistor

Vg is the gate voltage. When Vg is zero the injected spins which are transmitted through the

2DEG layer starts processing before they reach the collector, thereby reducing the net spin

polarization. Vg is the gate voltage. When Vg >> 0 the precession of the electrons is controlled

with electric filed thereby allowing the spins to reach at the collector with the same polarization.

Hence the net spin polarization is reduced

Traditional transistors use on-and-off charge currents to create bits—the binary zeroes and ones

of computer information. ―Quantum spin field effect‖ transistor will use up-and-down spin

states to generate the same binary data. One can think of electron spin as an arrow; it can point

upward or downward; ―spin-up and spin-down can be thought of as a digital system,

representing the binary 0 and 1. The quantum transistor employs also called ―spin-flip‖

mechanism to flip an up- spin to a downspin, or change the binary state from 0 to 1.

One proposed design of a spin FET (spintronic field-effect transistor) has a source and a drain,

separated by a narrow semi conducting channel, the same as in a conventional FET.

In the spin FET, both the source and the drain are ferromagnetic. The source sends spin-

polarized electrons in to the channel, and this spin current flow easily if it reaches the drain

unaltered (top). A voltage applied to the gate electrode produces an electric field in the channel,

which causes the spins of fast-moving electrons to process, or rotate (bottom). The drain impedes

the spin current according to how far the spins have been rotated. Flipping spins in this way

takes much less energy and is much faster than the conventional FET process of pushing charges

out of the channel with a larger electric filed.

One advantage over regular transistors is that these spin states can be detected and altered

without necessarily requiring the application of an electric current. This allows for detection

hardware that are much smaller but even more sensitive than today's devices, which rely on

noisy amplifiers to detect the minute charges used on today's data storage devices. The potential

end result is devices that can store more data in less space and consume less power, using less

costly materials. The increased sensitivity of spin transistors is also being researched in creating

more sensitive automotive sensors, a move being encouraged by a push for more

environmentally-friendly vehicles.

A second advantage of a spin transistor is that the spin of an electron is semi-permanent and can

be used as means of creating cost-effective non volatile solid state storage that does not require

the constant application of current to sustain. It is one of the technologies being explored for

Magnetic Random Access Memory (MRAM)

Spin transistors are often used in computers for data processing. They can also be used to

produce a computer's random access memory and are being tested for use in magnetic RAM.

This memory is superfast and information stored on it is held in place after the computer is

powered off, much like a hard disk.

Quantum Computer

The development of classical computers is still making enormous progress and no end of that

seems to be in sight. More over, the design of Quantum Computers seems to be very

questionable and almost surely enormously expensive. All this is true, However, there are four

very good reason for exploring Quantum Computing as much as possible.

Quantum computing is a challenge . A very fundamental and natural challenge According to

our current knowledge, our physical world is fundamentally quantum mechanical. All

computers are physical devices and all real computations are physical processes.

Quantum computing seems to be very must and actually our destiny. As miniaturization of

computing devices continues , we are rapidly approaching the microscopic level, where the

laws of the quantum world dominates.

Quantum computing is the potential . There are already results convincingly demonstrating

that for some important practical problems quantum computers are theoretically

exponentially more powerful than classical computer.

Finally, the development of quantum computing is a drive and gives new impetus to explore

in more detail and new points of view concepts, potentials, laws and limitations of the

quantum world and to improve our knowledge of the natural world.

The study of information processing laws, limitations and potentials is nowadays in general a

powerful methodology to extend our knowledge, and this seems to be particularly true for

quantum mechanics i.e related spintronics. Several profound insights into the natural world have

already been obtained on this basis.

In a quantum computer, the fundamental unit of information (called a quantum bit or qubit), is

not binary but rather more quaternary in name. This qubit property arises as a direct consequence

of its adherence to the laws of quantum mechanics. A qubit can exist not only in a state

corresponding to the logical state 0 or 1 as in a classical bit, but also in states corresponding to a

blend or superposition of these classical states. In other words, a qubit can exist as a zero, a one

or simultaneously as both 0 and 1, with a numerical coefficient representing the probability for

each state. Each electron spin can represent a bit; for instance, a 1 for spin up and 0 for spin

down. With conventional computers, Engineers go to great lengths to ensure that bits remain in

stable, well-defined states. A quantum computer, in contrast, lies on encoding information within

quantum bits, or qubits, each of which can exist in a superposition of 0 and 1. By having a large

number of qubits in superposition of alternative states, a quantum computer intrinsically contains

a massive parallelism.

Unfortunately, in most physical systems, interactions with the surrounding environment rapidly

disrupt these superposition states. A typical disruption would effectively change a superposition

of 0 and 1 randomly into either a 0 or a 1, as process called decoherence. State-of-the-art qubits

based on the charge of electrons in a semiconductor remain coherent for a few picoseconds at

best and only at temperatures too low for practical applications. The rapid decoherence occurs

because the electric force between charges is strong and long range. In traditional semiconductor

devices, this strong interaction is beneficial, permitting delicate control of current flow with

small electronic fields. To quantum coherent devices, however, it is a disadvantage. As a result,

an experiment was conducted on the qubits, which are based on the electron-spin. Electron-spin

qubits interact only weakly with the environment surrounding them, principally through

magnetic fields that are non-uniform in space or changing in time. Such fields can be effectively

shielded.

The goal of the experiment was to create some of these coherent spin states in a semiconductor

to see how long they could survive. Much to the surprise, the optically excited spin states in

ZnSe remained coherent for several nanoseconds at low temperatures—1,000 times as long as

charge-based qubits. The states even survived for a few nanoseconds at room temperature.

Subsequent studies of electrons in gallium arsenide (GaAs) have shown that, under optimal

conditions, spin coherence in a semiconductor is possible

Spintronics Scanner

Cancer cells are the somatic cells which are grown into abnormal size. The Cancer cells have

different electromagnetic sample when compared to normal cells. For many types of Cancer, it is

easier to treat and cure the Cancer if it is found early. There are many different types of Cancer,

but most Cancers begin with abnormal cells growing out of control, forming a lump that's called

a tumour. The tumour can continue to grow until the Cancer begins to spread to other parts of the

body. If the tumour is found when it is still very small, curing the Cancer can be easy. However,

the longer the tumour goes unnoticed, the greater the chance that the Cancer has spread. This

makes treatment more difficult. Tumour developed in human body, is removed by performing a

surgery. Even if a single cell is present after the surgery, it would again develop into a tumour. In

order to prevent this, an efficient route for detecting the Cancer cells is required. Here, in this

paper, we introduce a new route for detecting the Cancer cells after a surgery. This accurate

detection of the existence of Cancer cells at the beginning stage itself entertains the prevention of

further development of the tumour.

This spintronics scanning technique is an efficient technique to detect cancer cells even when

they are less in number.

An innovative approach to detect the cancer cells with the help of Spintronics: The following

setup is used for the detection of cancer cells in a human body:

(a) Polarized electron source

(b) Spin detector

(c) Magnetic Field

Polarized electron source:

A beam of electrons is said to be polarized if their spins point, on average, in a specific direction.

There are several ways to employ spin on electrons and to control them. The requirement for this

paper is an electron beam with all its electrons polarized in a specific direction. The following

are the ways to meet the above said requirement: Photoemission from negative electron affinity

GaAs Chemi-ionization of optically pumped meta stable Helium An optically pumped electron

spin filter A Wein style injector in the electron source A spin filter is more efficient electron

polarizer which uses an ordinary electron source along with a gaseous layer of Rb. Free

electrons diffuse under the action of an electric field through Rb vapour that has been spin

polarized in optical pumping. Through spin exchange collisions with the Rb, the free electrons

become polarized and are extracted to form a beam. To reduce the emission of depolarizing

radiation, N2 is used to quench the excited Rb atoms during the optical pumping cycle.

Spin detectors:

There are many ways by which the spin of the electrons can be detected efficiently. The spin

polarization of the electron beam can be analyzed by using:

(a)Mott polar meter (b)Compton polar meter (c)Miller type polar meter

Typical Mott polar meters require electron energies of ~100 kV. But Mini Mott polar meter uses

energies of ~25 k eV, requiring a smaller overall design. The Mini Mott polar meter has three

major sections: the electron transport system, the target chamber, and the detectors. The first

section the electrons enter is the transport system. An Engel lens configuration was used here.

Two sets of four deflectors were used as the first and last lens. The electrons next enter the target

chamber. The chamber consists of a cylindrical target within a polished stainless steel

hemisphere. A common material used for the high-Z nuclei target is gold. Low-Z nuclei help

minimize unwanted scattering, so aluminium was chosen. Scattered electrons then exit the target

chamber and are collected in the detectors. Thus there are many methods for detecting the spin

polarization of electrons.

External Magnetic Field:

An external magnetic field is required during this experiment. The magnetic field is applied after

the surgery has undergone. First, it is applied to an unaffected part of the body and then to the

surgery undergone part of the body. It is already mentioned that the magnetic field could easily

alter the polarization of electrons.

This technique using spintronics is suggested by us to identify tumour cells after surgery. The

procedure for doing this experiment is as follows:

Optical Spin Filter:

After surgery and the removal of the tumour, the patient is exposed to a strong magnetic field.

Now the polarized electron beam is applied over the unaffected part and spin orientation of

electrons are determined using polar meter. Then the same polarized beam is targeted over the

affected part of the body and from the reflected beam, change in spin is determined. Based on

these two values of spin orientation, the presence of tumour cells can be detected even if they are

very few in number. Hence, we suggest this method for the detection purpose. A detailed view of

this innovative approach is given as follows.

Spin Orientation of the unaffected part of the body: Applying Magnetic Field:

When the magnetic field is applied to the unaffected part of the human body, the normal somatic

cells absorbs the magnetic energy and retains it.

Determining the Spin orientation: -When the electrons get incident on the cells the magnetic

energy absorbed by the cells alters the spin orientation of the electrons.

These electrons get reflected and it is detected by the Mott polar meter. Then the change in spin

orientation of the electrons is measured as Sx.

Spin Orientation of the surgery undergone part of the body: Applying Magnetic Filter:

In the surgery undergone part of the body an external magnetic field is applied. The cancer cells

which are present, if any, will absorb more magnetic energy than the normal cells since they

differ in their electromagnetic pattern.

Determining the spin Orientation:

Now an electron beam which is polarized is incident on the surgery undergone part of the body.

The magnetic energy absorbed by the cancer cell alter the spin orientation of the electron beam.

Since cancer cells absorb more magnetic energy, the change in orientation caused by them is also

more. If no cancer cells are present the amount of change is equal to the previous case. The change

in spin is measured by the polar meter as Sy.

Inference:

If the change in the spin in the unaffected part of the body is same as that of the surgery

undergone part, i.e.

If Sx=Sy Then,

There are no cancer cells in the surgery undergone part of the body and all the cells have been

removed by the surgery.

If the change in spin in the unaffected part is not equal to the change caused by the surgery

undergone part of the body, i.e.

If Sx not equals Sy Then,

There are some cancer cells in the surgery undergone part of the body and the cancer cells are

not completely removed by the surgery. The steps involved are:

1) The patient is exposed to a strong magnetic field so that his body cell gets magnetized.

2) A beam of electrons with polarized spin is introduced on the unaffected part of the body and

the change in spin is detected by a polar meter.

3) A beam of electrons with polarized spin is introduced on the part which had undergone

surgery. And the corresponding change in spin be Y

4) If X - Y = 0, it indicates that cancer cells have been removed from the body, if not it indicates

the presence of traces of cancer cells and it has to be treated again for ensuring complete

safety to the patient.

Thus this technique efficiently identifies the presence of cancer cells in that part of the body that

has undergone surgery to prevent any further development.

ADVANTAGES OF SPINTRONICS

As most of the spintronics devices/applications are on paper all the advantages are just defined

based on theoretical findings and they may have some dis-advantages which will/may be known

after they are fabricated and used. Some of the advantages of spintronics are:

The spin devices act as multi-functional units

Low power consumption.

Compact and Faster Devices

Larger storage capacity

The MRAM has all the properties of DRAM ,SRAM and ROM and hence single memory

chip can be used instead of three memory chips

Spintronics does not require unique and specialized semiconductors; can be implemented

or with common metals, such as Copper, Aluminium and Silver.

Since Spins don‟t change when power is turned off, the memory remains non-volatile.

Disadvantages of Spintronics

Controlling the spin for long distances

Silicon causes electrons to lose their spin state.

Major challenges are:.

Transport of spin polarized carriers across relevant length scales

Manipulation of both electron and nuclear spins on sufficiently fast time scales

Real Time Applications

The applications of spin devices and hence spintronics are vast since it provides many

advantages such as speed and size. . Some of the potential applications are:

Spin LED

Spin FET

MRAM

MRAM:-

The MRAM is the form of the RAM and is acronym for Magnetic Random Access Memory.

MRAM basically uses a spin device known as Magnetic Tunnel Junction. The property of

Tunnel magneto résistance [MTR] of the MTJ is used in MRAM. The relative change of MTR

can reach 70% at room temperature. The figure below shows the structure of the MTJ as well as

MRAM.

The MRAM is presently under development and is expected to reach similar densities and access

times as the current SRAM and DRAM, but their main advantages on these volatile

semiconductor- based memories is that they retain data even after losing power and hence to

helps to decrease the boot – up time of computers.

As shown in the figure each junction can store a bit of data. If the polarization of spin is in

parallel at both the layers, the resistance will be less and we say that a bit “0” is stored. And if

the spin polarization is anti – parallel then resistance is high and we say a bit “1” is stored. The

main advantage of MRAM is that it can attain a writing speed of 1000 times to that of the present

RAM’s.

SPIN FET:-

The figure above the structure and working of Spin FET. As shown the Source and Drain areas

are fabricated using Ferro-magnetic material and the channel is fabricated using the

semiconductor material. The additional gating effect is via the magnetic field.

The working of the spin FET is illustrated in the upper part of the figure. It illustrates the physics

of devices where both injection of spins into semiconductor and detection of spin information are

electrical. The ideal situation is when the spin lifetime is much longer than spent by the carriers

in semiconductor.

As shown a spin polarized current is then easily transmitted in the parallel configuration of

emitter and collector, whereas the anti-parallel one leads to spin accumulation and current

blockade.

SPIN LED:-

The figure above shows the structure of spin LED. The LED has a heterostructure as shown.

Spin – polarized electrons are injected from a paramagnetic DMS into a GaAs/AlGaAs LED,

which leads to emission of circularly polarized light. An injection efficiency of 90% spin

polarized current has been demonstrated with this structure.

Some other applications-

Laptop hard drives

4GB Compact Flash card

iPod nano

CONCLUSION AND FUTURE SCOPE

Conclusion:-

In this report we have seen the advantages of spintronics devices over the present electronic

devices. As said earlier this is the technology which will replace the present electronics era and

provides the advantages of speed, size, compactness so on. If the applications such as LED and

MRAM can be realized we can attain high efficiency of output in the case of LED and we can

attain high writing speed and reading efficiency in the case of MRAM.

Spintronics is one of the most exciting and challenging areas in nanotechnology, important to

both fundamental scientific research and industrial applications. These spintronics-devices,

combining the advantages of magnetic materials and semiconductors, are expected to be non-

volatile, versatile, fast and capable of simultaneous data storage and processing, while at the

same time consuming less energy.

They are playing an increasingly significant role in high-density data storage, microelectronics,

sensors, quantum computing and bio-medical applications, etc.

It is expected that the impact of spintronics to the microelectronics industry might be comparable

to the development of the transistor 50 years ago.

Though the area of spintronics has some drawbacks which will be realized when the spin devices

will be fabricated we may still avoid these drawbacks to large extent.

One drawback of this emerging technology is that since the spintronics is mainly based on the

magnetic properties of the material, the magnetic field of the earth may affect the magnetic field

inside the spin devices and cause errors. One main disadvantages of this is that the data stored in

a MRAM may be altered and hence can lead to errors.

Hopefully, this and many unknown effects will be found out and efforts are made to avoid such

effects and lead to more reliable, more functional, with greater speed of operation of spin devices

will be achieved.

Future Scope :-

Spintronics is still in its infancy and it‟s difficult to predict how it will evolve.

New physics is being discovered and new materials are being developed, such as magnetic

semiconductors

Several experiments have been carried out for progress in transporting spins over long distances

and in high electric fields that will probably prove successful in the near future.

Spintronics in INDIIA -

The technology wherein both the charge and spin of an electron is used to carry information has

generated excitement for its potential in a wide range of applications.

"The first applications of spintronics having been demonstrated, there is tremendous interest in

the development of the next spintronics device.

Spintronics biggest potential lies in embedded memories and non-volatile memory devices such

as magneto resistive random access memory (MRAM), which will revolutionize the memory

market.

Other applications include the use of spintronics in quantum computation and the development

of the quantum computer. Spin transistors are also could well challenge the monopoly of

semiconductor electronics.

Research in spintronics faces several challenges, especially handling-related issues. Because

spintronics devices use magnetism and materials such as nickel, iron, cobalt — with alloys not

commonly used in normal

semiconductor electronics — there are difficulties in etching and patterning as well as in

integrating the magnetic material into a silicon process for manufacturing MRAMs.

The behaviour of the magnetic element on a chip in both read and write modes could be quite a

hurdle it is required to make MRAMs reliable.

Today everyone already has a spintronics device on their desktop, as all modern computers use

the spin valve in order to read and write data on their hard drive. It was followed immediately by

the discovery of Tunnelling Magneto resistance (TMR) leading to the magnetic tunnel junction

that has been utilized for the next generation computer memory known as Magnetic Random

Access Memory (MRAM), another spintronics device for computers. Therefore, the initial

driving force for spintronics has been the improvement of computer technology. At present the

research has been concentrating on the fabrication of spin transistors and spin logics devices

integrating magnetic and semiconductors, with the aim of improving the existing capabilities of

electronic transistors and logics devices so that the future computation and thus the future

computer could become faster and consume less energy.

There are four main areas in spintronics:

1)Understanding the fundamental physics, such as spin-dependant transports across the

magnetic/ semiconductor interfaces and spin coherence length in semiconductors.

2) Synthesising suitable spintronics materials with Curie temperatures above room temperature,

large spin polarisation at the Fermi level and matching conductivity between the magnetic and

semiconductor materials.

3) Fabricating devices with nanometre feature sizes and developing new techniques for mass

production.

4) Integrating spin-devices with current microelectronics and computing.

REFERENCES

1) N Taniguchi, “On the basic concepts of Nano Technology” Proc. Intl conference prod

engage, Tokyo (Journal Paper)

2) www.physik.uni-regensburg.de/.../Spintronics

3) http://www.slideshare.net

4) Das Sarma, S., et al. 2000. Theoretical perspectives on spintronics and spin-polarized

transport. IEEE Transactions on Magnetics

Books:-

5) Rainer Wiser (2nd edition), “Nano electronics and information technology - Advanced

electronic materials & devices”

6) Electronic measurement and control of spin transport (Technical Publication)

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