Spintronics_report by Ajay Kumar

8/3/2019 Spintronics_report by Ajay Kumar

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SPINTRONICS TECHNOLOGY

A COLLOQUIUM REPORT

Submitted by

Mr. AJAY KUMAR(2008EEC13)

in partial fulfillment for the award of the degree

of

BACHLEOR OF TECHNOLOGY

IN

ELECTRONICS & COMMUNICATION ENGINEERING

At

SCHOOL OF ELECTRONICS AND COMMUNICATIONENGINEERING

SHRI MATA VAISHNO DEVI UNIVERSITYKATRA

NOVEMBER 2011


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I hereby certify that the work which is being presented in the

B.Tech. colloquium report Spintronics Technology, in partial fulfillment of the

requirements for the award of the Bachelor of Technology in Electronics &

Communication Engineering and submitted to the School of Electronics &

Communication Engineering of Shri Mata Vaishno Devi University, Katra, J&K is

an authentic record of my own work carried out during a period from August 2011to Dec 2011under the supervision of Mr. Ashish Suri, Lecturer, School of

Electronics and Communication Engineering.The matter presented in this thesis has not been submitted by me for the

award of any other degree elsewhere.

AJAY KUMAR

(2008EEC13)

This is to certify that the above statement made by the candidate is correct to

the best of my knowledge.

Mr. Ashish Suri

Colloquium Incharge

Date:

Dr. Vipan KakkarDirectorSchool of Electronics & Communication Engineering Department

Shri Mata Vaishno Devi University, Katra, J&K


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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 characterized as spin upor spin down.

Conventional electronic devices rely on the transport of electrical

charge carrierselectronsin 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 electrons spin to perform their functions form thefoundations of spintronics (short for spin-based electronics), also known as

magnetoelectronics. Spintronics devices are smaller than 100 nanometer in size,

more versatile and more robust than those making up silicon chips and circuitelements. 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 Magnetoresistance

(GMR). It results from subtle electron-spin effects in ultra thin multilayers 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 Magnetoresistance.


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Contents

1. Introduction 6

2. Basic Principle 7

2.1 Fundamentals of Spin .........................................................................7

3. Giant Magnetoresistance 9

3.1 Construction of GMR10

3.2 Spin Valve GMR ......................................12

4. Spintronics Devices 13

4.1 MRAM (Magnetoresistive Random Access Memory).......................13

4.2 SPIN TRANSISTORS........................................................................14

4.3 Spintronics Scanner.............................................................................16

5. PROS & CONS of SPINTRONICS 20

5.1 WHY SPINTRONICS? ......................................................................20

5.2 CHALLENGING-OBSTACLES.......................... .21

6. CONCLUSION 21

7. REFERENCES 22


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ACKNOWLEDGEMENT

Successful completion of any task is unimaginable without appreciating the

people associated with it. So, after the completion of this colloquium report, I

would like to express my regards to all the persons who contributed with theirhelping hands, whether in a direct or indirect way.

With due respect, I express my heartfelt thanks to Prof. Vipan Kakkar,

Director, School of Electronics & Communication Engineering, SMVDU for his

assistance and constant source of encouragement and for providing me his valuable

guidance and sharp vision to explore about the topic of Spintronics Technology .

I express my deep and devoted gratitude to Mr. Ashish Suri for granting me

the permission to work upon Spintronics Technology and for providing me all the

required facilities.

I cannot close this prefatory remark without expressing my deep sense of

gratitude to my dear parents for their blessings and endeavor to keep my moral

high.


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1. INTRODUCTION

Conventional electronic devices rely on the transport of electrical charge carrierselectrons in a

semiconductor such as silicon. Now, however, physicists are trying to exploit the spin ofthe

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 todays 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 thetransport of electric charge carries-electrons. But there are 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.

Howard Johnson is father of the breakthrough science called spintronics.

Electrons, in addition to their negative charge, also possess a spin (properties of a small magnet).


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2.BASIC PRINCIPLE

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 0and1in logical operations. Spin is the characteristic 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 particles axis of spin.

2.1Fundamentals 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.

3. Scientists represent the spin with a vector. For a sphere spinning west to east, the vector

points north or up. It points southor downfor the spin from east to west.

4. In a magnetic field, electrons with spinup 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.


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

Imagine a small electronically charged sphere spinning rapidly. The circulating charges in the

sphere amount to tiny loops of electric current which creates a magnetic field. A spinning spherein an external magnetic field changes its total energy according to how its spin vector is aligned

with the spin. In some ways, an electron is just like a spinning sphere of charge, an electron has a

quantity of angular momentum (spin) an associated magnetism. In an ambient magnetic field and

the spin changing this magnetic field can change orientation. Its energy is dependent on how its

spin vector is oriented. The bottom line is that the spin along with mass and charge is defining

characteristics of an electron. 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 the differences in the transport of spin-up and

spin-down electrons.


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3.Giant Magnetoresistance

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

one direction or the othercalled 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 magnetized 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 heads electrical resistance an effect

called magnetoresistance.

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

much more powerful effect called giant magnetoresistance (GMR). It results from subtle

electron-spin effects in ultra-thin multilayers of magnetic materials, which cause huge changes

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

ordinary magnetoresistance. IBM 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. 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). 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 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.


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The effect is observed as a significant change in the electrical resistance depending on

whether the magnetization of adjacent ferromagnetic layers are in a parallel or an antiparallel

alignment. The overall resistance is relatively low for parallel alignment and relatively high for

antiparallel alignment.

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

Magnetoresistance (GMR). GMR is a quantum mechanical magnetoresistance effect observed in

thin film structures composed of alternating ferromagnetic and non magnetic layers. The 2007

Nobel Prize in physics was awarded to Albert Fert and Peter Gruenberg for the discovery of

GMR.

Giant magnetoresistance (GMR) came into picture in 1988, which lead the rise of

spintronics. It results from subtle electron-spin effects in ultra-thin multilayers of magneticmaterials, which cause huge changes in their electrical resistance when a magnetic field is

applied. GMR is 200 times stronger than ordinary magnetoresistance. 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.

3.1Construction 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 amagnetic 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. When a current passes through the Ferro magnet, electrons of one

spin direction tend to be obstructed.

A ferromagnetic 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


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of the recorded 1s and 0`s change the second layers 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 tunneling magnetoresistance (TMR) spin valves which

enable disk drive densities exceeding 1 Terabyte per square inch.

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

magnetoresistance 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.

Magnetocoupler is a device that uses giant magnetoresistance (GMR) to couple two electricalcircuits galvanically 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.

Fig. A GMR Device


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3.2 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. Standard geometry for GMR based Spin Valves

An electron passing through the spin-valve will be scattered more if the spin of the electron isopposite to the direction of the magnetization in the FM layer.

Fig .GMR based Spin Valves for read head in hard drives


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4. Spintronics Devices

Spintronics 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.

Some of the Spintronics devices are:

Magnetoresistive Random Access Memory(MRAM) Spin Transistor Quantum Computer Spintronics Scanner

4.1MRAM (Magnetoresistive 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 mustconstantly feed the capacitor with power because the charge you put into the capacitor is

constantly leaking out.

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 1s and 0s.


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Fig. 256 K MRAM

4.2 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 upwardor 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 (spintronics 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 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 large spin diffusion lengths. The injected spins which are transmitted


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through this layer start processing as illustrated in Figure before they reach the collector

due to the spin-orbit coupling effect.

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 samepolarization.

Hence the net spin polarization is reduced. In order to solve this problem an electric

field is applied perpendicularly to the plane of the film by depositing a gate electrode

on the top to reduce the spin-orbit coupling effect as illustrated in Figure. By controlling

the gate voltage and polarity can the current in the collector can be modulated there by

mimicking the MOSFET of the conventional electronics. Here again the problem of

conductivity mismatch between the source and the transmitting layer is an important issue.

The interesting thing would be if a Haussler alloy is used as the spin source and a

semi metallic Haussler alloy as the transmitting layer, the problem of conductivity mismatchmay be solved. Since both the constituents are of same structure the possibility of

conductivity mismatch may be less. Traditional transistors use on-and-off charge currents to

create bitsthe 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


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also called spin-flip mechanism to flip an upspin to a downspin, or change the binary state from

0 to 1.

One proposed design of a spin FET (spintronics 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- polarizedelectrons 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'sdevices, 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.

4.3Spintronics 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 tumor. The tumor can continue to grow until the

Cancer begins to spread to other parts of the body. If the tumor is found when it is still

very small, curing the Cancer can be easy. However, the longer the tumor goes unnoticed,

the greater the chance that the Cancer has spread. This makes treatment more difficult.


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Tumor 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 tumor. 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 tumor. 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 specificdirection. 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 vapor 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 polarimeter (b) Compton polarimeter (c) Moller type polarimeter

Typical Mott polarimeter requires electron energies of ~100 kV. But Mini Mott polarimeter uses

energies of ~25 keV, requiring a smaller overall design. The Mini Mott polarimeter has threemajor sections: the electron transport system, the target chamber, and the detectors. The first

section the electrons enter is the transport system. An Einsel 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 aluminum was chosen. Scattered electrons then exit the target


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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 afterthe 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 tumor cells after surgery.

The procedure for doing this experiment is as follows: ---

Optical Spin Filter:--

After surgery and the removal of the tumor, the patient is exposed to a strong magneticfield. Now the polarized electron beam is applied over the unaffected part and spin

orientation of electrons are determined using polarimeter. 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 tumor cells can be

detected even if they are very few in numbers. 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

polarimeter. 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:-


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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 alters 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 polarimeter 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!=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 polarimeter. Let it be X

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.


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5. PROS & CONS of SPINTRONICS---

5.1 WHY SPINTRONICS?

Though there are so many other technologies like carbon nanotubes, which are also on their wayto revolutionize the electronic industry, but spintronics has some special features, which makes it

the higher hand among other technologies.

It combines logic, storage and sensor applications. The technology could ultimately shrink storage to one trillion bits per square inch,

enabling the storage of 50 or more DVDs on a hard drive the size of a credit card.

Restricting the movement of information based on electron spin, rather than charge, canincrease computing power exponentially and, by including memory with processing,

create "a sort of computer on a chip".

These spintronics devices might lead to quantum computers and quantumcommunication based on electronic solid-state devices, thus changing the perspective ofinformation technology in the 21st century.

More importantly, these devices could be fabricated with many of the tools already usedin the electronics industry, thereby speeding up their development.

The remarkable new generation of spintronics devices are smaller, more versatile andmore robust than those currently making up silicon chips and circuit elements.

Because the spin orientation of conduction electrons survives for a relatively long time,spintronics devices are particularly attractive for memory storage and magnetic sensorsapplications and potentially for quantum computing.

It could even lead to computers that boot up instantly. Normal electronics, encode computer data based on a binary code of ones and zeros. But

even the direction of a spinning electron -- either spin up or spin down -- can also beanalogous to the 1s and 0s.

One important aspect where spin based devices score over charge based devices is thatas in the case of charge based electronics we pack more devices together, which heats up

the chip. This is totally eliminated when we use the spin based electronics.

A magnetic chip could use much less power than conventional electronics. This is idealfor mobile communications and laptop computersbattery sizes could be considerably

reduced or recharging made obsolete.

Another advantage is that magnetic chips can be made out of just a few layers of metaland would be easier and cheaper to manufacture, than current electronic circuits.

Magnetic chips are also tougher: one of the important applications could be in space,where they would replace electronics that require protection from solar radiation, whichroutinely disrupts satellites when there are solar storms.

In modern military nuclear bombs, which scatter high pulses of electromagneticradiations, the computers with this technology can withstand any blast.


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5.2 CHALLENGING-OBSTACLES

It would be incomplete not to visit the other face of this growing technology after relishing themost soughed advantages of it. The challenging obstacles before us posed by this glorious

technology may include:

The main drawback being it is difficult to make integrated spintronics devices that arecontrolled by magnetic fields. An external magnetic field could not offer individual control

over each spin transistor on a chip. The magnetic field, which is used to control or change the

spin of one electron, may end up in changing spins of many electrons in the vicinity.

Can we devise economic ways to combine ferromagnetic metals and semiconductors inintegrated circuits?

Can we make semiconductors that are ferromagnetic at room temperature? What is an efficient way to inject spin-polarized currents, or spin currents, into a semiconductor? What happens to spin currents at boundaries between different semiconductors? How

long can a spin current retain its polarization in a semiconductor?

Spintronics researchers have also demonstrated a spin light-emitting diode, and spin transistors and spin-

based optical switches for communications networks are probably another safe bet for the future. In the

near term, we can expect to see substantial improvements that will rapidly become indispensable features

in some of our electronic devices.

CONCLUSION

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.

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 Tunneling Magnetoresistance (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


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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 themagnetic/ semiconductor interfaces and spins coherence length in semiconductors.

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

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

semiconductor materials.

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

production.

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

REFERENCES

1. IEEE Digital Explore Library

2. School of Physics & Astronomy, University of Nottingham

3. Department of Physics and MARTECH, Florida State University

4. Department of Physics and Center for Advanced Photonic and Electronic Materials

University at Buffalo, The State University of New York

5. Research Councils UK

www.rcuk.ac.uk

6. Engineering and Physical Sciences Research Council (EPSRC)

www.epsrc.ac.uk

7. Particle Physics and Astronomy Research Council (PPARC)

www.pparc.ac.uk

8. Council for the Central Laboratory of the Research Councils

www.cclrc.ac.uk


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Spintronics_report by Ajay Kumar

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