spintronics

SPINTRONICS

1.1 INTRODUCTION

An emerging research field in physics focused on spin-dependent phenomena

applied to electronic devices is called spintronics. The promise of spintronics is

based on manipulation not only of the charge of electrons, but also their spin, which

enables them to perform new functions. Currently, the ability to manipulate electron

spin is expected to lead to the development of remarkable improvements in

electronic systems and devises used in photonics, data processing and

communications technologies only.

1.2 BRIEF HISTORY

During the last half of the 20th century, the world witnessed a revolution based on a

digital logic of electrons. The spintronics dream is a seamless integration

justification, could be called the microelectronics era. From the earliest transistor to

the remarkably powerful microprocessor in desktop computer, most electronic

devices have employed circuits that express data as binary digits, or bits—ones and

zeroes represented by the existence or absence of electric charge.

Furthermore, the communication between microelectronic devices occurs by the

binary flow of electric charges. The technologies that emerged from this simple logic

have created a multitrillion dollar per year global industry whose products are

ubiquitous. Indeed, the relentless growth of microelectronics is often popularly

summarized in Moore’s Law, which holds that microprocessors will double in power

every 18 months as electronic devices shrink and more logic is packed into every

chip. Yet even Moore’s Law will run out of momentum one day as the size of

individual bits approaches the dimension of atoms—this has been called the end of

the silicon road map.

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For this reason and also to enhance the multifunctionality of devices, another property

of the electron has been exploited—a characteristic known as spin. Spin is a purely

quantum phenomenon. The electrons have spin pointing either “up” or “down” in relation

to a magnetic field. Spin therefore lends itself elegantly to a new kind of binary logic of

ones and zeros. The movement of spin, like the flow of charge, can also carry information

among devices.

1.3 SPINTRONICS

Spintronics is a new, quickly developing field of science and technology, which deals

with relationships responsible for specific features of the spin interactions in metals,

semiconductors doped with transition or rare earth elements, and hetero structures that

ensure unique properties of these materials.

An electron is just like a spinning sphere of charge. It has a quantity of angular

momentum (its "spin") and an associated magnetism, and in an ambient magnetic field its

energy depends on how its spin vector is oriented. Every electron exists in one of two

states, namely, spin-up and spin-down with its spin either +1/2 or –1/2. In other words, an

electron can rotate either clockwise or counterclockwise around its own axis with

constant frequency. . Two spins can be "entangled" with each other, so that neither

distinctly up nor down, but a combination of the two possibilities.

The main avenues of the development of spintronics are

i) fabrication of magnetic nanostructures including novel materials, thin films, hetero

structures, and multifunctional materials;

ii) research on magnetism and spin control of magnetic nanostructures, theory of

ferromagnetic exchange in dilute magnetic semiconductors (DMS),tunneling effects and

spin injection, as spin transport and detection of magnetism;

iii) magneto electronics and devices employing the giant magneto resistance (GMR)

effect, tunneling devices, semiconductor hetero structures for spin injection, spin

transport and detection, and pulsed ferromagnetism;

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iv) magneto optical properties of dc magnetic semiconductor hetero structures and

time resolved experiments, optical spin injection and detection, optically induced

ferromagnetism, ultrafast magneto optic switches; and quantum information

transmission;

v) pattern recognition; imaging and metrology including magnetic pattern recognition and

anomalous Hall effect; and

vi) instrument engineering and applied studies.

In order to make a spintronic device, the primary requirement is to have a system that can

generate a current of spin polarized electrons, and a system that is sensitive to the spin

polarization of the electrons. Most devices also have a unit in between that change the

current of electrons depending on the spin states.

The simplest method of generating a spin polarized current is to inject the current

through a ferromagnetic material. The most common application of this effect is a giant

magneto resistance (GMR) device. A typical GMR device consists of at least two layers

of ferromagnetic materials separated by a spacer layer. When the two magnetization

vectors of the ferromagnetic layers are aligned, then an electrical current will flow freely,

whereas if the magnetization vectors are anti parallel then the resistance of the system is

higher. Two variants of GMR have been applied in devices, current-in-plane where the

electric current flows parallel to the layers and current-perpendicular-to-the-plane where

the electric current flows in a direction perpendicular to the layers.

1.4 THE LOGIC OF SPIN

Spin relaxation (how spins are created and disappear) and spin transport (how spins move

in metals and semi- conductors) are fundamentally important not only as basic physics

questions but also because of their demonstrated value as phenomena in electronic

technology.

Spins can arrange themselves in a variety of ways that are important for spintronics

devices. They can be completely random, with their spins pointing in every possible

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direction and located throughout a material in no particular order (upper left). Or these

randomly located spins can all point in the same direction, called spin alignment (upper

right). In solid state materials, the spins might be located in an orderly fashion on a

crystal lattice (lower left) forming a nonmagnetic material. Or the spins may be on a

lattice and be aligned as in a magnetic material (lower right),

Fig 1.1 Spin alignment in unmagnetized and magnetized field

One device already in use is the giant magnetoresistive, or GMR, sandwich structure,

which consists of alternating ferromagnetic (that is, permanently magnetized) and

nonmagnetic metal layers. Depending on the relative orientation of the magnetizations in

the magnetic layers, the electrical resistance through the layers changes from small

(parallel magnetizations) to large (antiparallel magnetizations).

Investigators discovered that they could use this change in resistance (called

magnetoresistance, and “giant” because of the large magnitude of the effect in this case)

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to construct exquisitely sensitive detectors of changing magnetic fields, such as those

marking the data on the types of computations than is possible with electron-charge-

based systems. Spintronic disk drive read/write heads have been wildly successful,

permitting the storage of tens of gigabytes of data on notebook computer hard drives, and

has created a billion-dollar per year industry. Groups have also been working to develop

nonvolatile memory elements from these materials, possibly a route to instant-on

computers.

1.5 ADVANTAGE OF SPIN OVER CHARGE

One advantage of spin over charge is that spin can be easily manipulated by externally

applied magnetic fields, a property already in use in magnetic storage technology.

Another more subtle (but potentially significant) property of spin is its long coherence, or

relaxation, time—once created it tends to stay that way for a long time, unlike charge

states, which are easily destroyed by scattering or collision with defects, impurities or

other charges. These characteristics open the possibility of developing devices that could

be much smaller, consume less electricity and be more powerful for certain of electronic,

optoelectronic and magnetoelectronic multifunctionality on a single device that can

perform much more than is possible with today’s microelectronic devices.

1.6 DEVELOPMENT OF SPINTRONIC DEVICES

Researchers and developers of spintronic devices currently take two different approaches.

In the first, they seek to perfect the existing GMR-based technology either by developing

new materials with larger populations of oriented spins (called spin polarization) or by

making improvements in existing devices to provide better spin filtering. The second

effort, which is more radical, focuses on finding novel ways both to generate and to

utilize spin-polarized currents—that is, to actively control spin dynamics. The intent is to

thoroughly investigate spin transport in semiconductors and search for ways in which

semiconductors can function as spin polarizer’s and spin valves.

This is crucial because, unlike semiconductor transistors, existing metal-based devices do

not amplify signals (although they are successful switches or valves).

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1.7 SPINTRONIC DEVICE

The first scheme for a spintronic device based on the metal-oxide-semiconductor

technology familiar to microelectronics designers was the field effect spin transistor

proposed in 1989 by Supriyo Datta and Biswajit Das of Purdue University.

In a conventional field effect transistor, electric charge is introduced via a source

electrode and collected at a drain electrode. A third electrode, the gate, generates an

electric field that changes the size of the channel through which the source-drain current

can flow, akin to stepping on a garden hose. This results in a very small electric field

being able to control large currents.

In the Datta-Das device, a structure made from indium-aluminum-arsenide and indium-

gallium-arsenide provides a channel for two-dimensional electron transport between two

ferromagnetic electrodes. One electrode acts as an emitter, the other a collector (similar,

in effect, to the source and drain, respectively, in a field effect transistor). The emitter

emits electrons with their spins oriented along the direction of the electrode’s

magnetization, while the collector (with the same electrode magnetization) acts as a spin

filter and accepts electrons with the same spin only. In the absence of any changes to the

spins during transport, every emitted electron enters the collector.

In this device, the gate electrode produces a field that forces the electron spins to process,

just like the precession of a spinning top under the force of gravity. The electron current

is modulated by the degree of precession in electron spin introduced by the gate field: An

electron passes through the collector if its spin is parallel, and does not if it is antiparallel,

to the magnetization. The Datta-Das effect should be most visible for narrow band-gap

semiconductors such as InGaAs, which have relatively large spin-orbit interactions (that

is, a magnetic field introduced by the gate current has a relatively large effect on electron

spin). Despite several years of effort, however, the effect has yet to be convincingly

demonstrated experimentally.

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The all-metal spin transistor is tri-layer structure consists of a nonmagnetic metallic layer

sandwiched between two ferromagnets. The all-metal transistor has the same design

philosophy as do giant magnetoresistive devices: The current flowing through the

structure is modified by the relative orientation of the magnetic layers, which in turn can

be controlled by an applied magnetic field. In this scheme, a battery is connected to the

control circuit (emitter- base), while the direction of the current in the working circuit

(base-collector) is effectively switched by changing the magnetization of the collector.

The current is drained from the base in order to allow for the working current to flow

under the “reverse” base-collector bias (antiparallel magnetizations). Neither current nor

voltage is amplified, but the device acts as a switch or spin valve to sense changes in an

external magnetic field.

(a) (b)

Fig 1.2 The Spin transistor when ferromagnets are (a) aligned ; (b) non-aligned

In the spin transistor , two ferromagnetic electrodes-the emitter and collector—sandwich

a nonmagnetic layer—the base. When the ferromagnets are aligned, current flows from

emitter to collector (left). But when the ferromagnets have different directions of

magnetization, the current flows out of the base to emitter and collector (right).

A potentially significant feature of the all-metal spin transistor is that, being all metallic,

it can in principle be made extremely small using nano lithographic techniques (perhaps

as small as tens of nanometers). An important disadvantage of this transistor is that, being

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all-metallic, it will be difficult to integrate this spin transistor device into existing

semiconductor microelectronic circuitry.

A critical disadvantage of metal-based spintronic devices is that they do not amplify

signals. There is no obvious metallic analog of the traditional semiconductor transistor in

which draining one electron from the base allows tens of electrons to pass from the

emitter into the collector (by reducing the electrostatic barrier generated by electrons

trapped in the base)

DETECTION OF CANCER CELLS

2.1 CANCER CELLS

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

have different electromagnetic pattern 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. 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 method for detecting the cancer cells is required

It is very important that the cancer cells should be diagnosed at the earlier stages itself

failing which develop rapidly into acute tumors.

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2.2 DIAGNOSTIC AND STAGING INVESTIGATIONS

Today there are a growing number of tests that can be performed to identify the presence

of abnormal cells or an abnormal structure. These tests can initially be undertaken to

confirm or eliminate a primary cancer (diagnose), or they can be performed to help in

determining the spread of the malignancy (stage). Essentially these investigations fall into

three main groups:

Radiology (diagnostic imaging)

Pathology

Endoscopy

2.3 RADIOLOGY (DIAGNOSTIC IMAGING)

Radiology, or diagnostic imaging, allows for visualization of the internal structures.

Images are created that the radiologist then interprets. These images can be created in a

number of ways.

2.3.1 X-RAYS

X-rays or gamma rays are passed through a particular part of the body to generate an

image, e.g. a chest radiograph or a mammogram. To achieve a clearer image, especially

in the gastrointestinal tract, lymphatic vessels, urinary tract, etc., contrast medium can be

used. This involves injecting or, in the case of gastrointestinal

studies, asking the patient to swallow a contrast medium. These contrast media enhance

the structures, so providing the clinicians with more detailed information .

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Fig 2.1 Diagnosis using X-rays

The most important problem with X-Rays is the danger they pose due to prolonged

exposure. The radiation can cause damage to the soft tissues. X-Rays use radiation in

order to get an internal view of the body and hence many X-Rays cannot be taken at a

single time. The rays are so powerful that they can knock electrons off of the atoms when

they hit them. The result is the production of ions that create many abnormal reactions in

the body. X-Rays have the ability to alter DNA as well. But with the MRI several cross

sectional images can be taken at the same time without creating any biological hazards.

2.3.2 COMPUTED TOMOGRAPHY

Computed tomography (CT) is an X-ray technique that involves taking a series of

radiographs in ‘slices’. The images are then analyzed by a computer to produce a three-

dimensional picture

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.

Fig 2.2 Block Diagram of the CT-Scanner

Due to the high contrast resolution of CT scanning, differences between the tissues are

more apparent compared to other techniques. Further, imaging in CT scan removes the

superimposition of structures other than the area of interest. The data from a single

procedure can be viewed in different planes and thus increases diagnostic ability. This

technique is also popular because it can be used to diagnose a number of conditions. This

might eliminate the need for other diagnostic techniques such as colonoscopy.

CT scans are associated with the risk of causing cancers, such as lung cancer, colon

cancer and leukemia This is mainly due to the use of X-rays. . There are other safety

concerns associated with the use of contrast agents which are administered intravenously.

However, these disadvantages can be reduced with the use of lower doses.

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PATHlOLOGY:

pathology tests can be used to confirm a clinical diagnosis and, more recently, to monitor

a patient’s disease and response to treatment. The types of pathology tests that can be

undertaken include the following.

Pathology tests can be used to confirm a clinical diagnosis and, more recently, to monitor

a patient’s disease and response to treatment. The types of pathology tests that can be

undertaken include the following.

Pathology tests can be used to confirm a clinical diagnosis and, more recently, to monitor

a patient’s disease and response to treatment. The types of pathology tests that can be

undertaken include the following.

2.4.1 BIOCHEMISTRY

Body fluids such as blood, urine, etc. can be used to identify values that fall outside the

range expected in a ‘healthy’ individual, e.g. an elevated bilirubin and alkaline

phosphates could be indicative of liver disease. A raised calcium could indicate bone

metastases.

2.4.2 MONOCLONAL ANTIBODIES

The production of monoclonal antibodies can lead to the detection of specific tumor

antigens .

2.4.3 TUMOUR MARKERS

These are proteins, antigens, genes or enzymes that can be produced by a tumour. These

tests of body fluids, including blood, can be useful in reaching a diagnosis or monitoring

an individual’s disease.

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2.4.4 BIOPSY

A biopsy provides tissue for histological examination.

2.4.5 CYTOLOGY

This involves looking at cells that have been obtained from fluid, secretions or washings

from irrigation of cavities or brushing from tissues.

2.5 ENDOSCOPY

This involves the passage of a long flexible bundle of fiber optic lights. Images are

reflected back to the head of the endoscope to provide the operator with a clear picture of

the tissues/organs being viewed. It is possible for the operator to obtain samples of tissue

for histological examination. A pair of special forceps is passed through the endoscope to

the area requiring biopsy. The tissue is then retrieved through the endoscope and sent to

the laboratory. Cells for cytological examination can also be obtained via endoscopic

examinations

DETECTING THE CANCER CELLS WITH THE HELP OF

SPINTRONIC SCANNER

An innovative idea of extending the hands of spintronics in MEDICAL FIELD has been

developed, in the detection of cancer cells even when they are very few in number in the

human body.

This approach is relied on two important aspects:

(i) the behavior of electron spin in a magnetic field

(ii) the cancer cell’s abnormality over normal cells.

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3.1 CANCER CELLS

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

have different electromagnetic pattern when compared to normal cells.

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 method for detecting the cancer cells is required.

Thus a new method for detecting the cancer cells after a surgery has been developed. This

accurate detection of the existence of cancer cells at the beginning stage itself ensures the

prevention of further development of the tumor.

3.2 PROPERTIES OF SPIN:

• The spin of an electron has a great dependence over an external magnetic field. If a

polarized electron is exposed in a magnetic field, its spin orientation gets varied. This

behavior of the electron plays a crucial role in the presented approach in this paper.

• Polarization of spin of electrons is possible so that the spin of all electrons orient in a

particular direction.

• The electron spin can be detected by using devices like polarimeters.

• The electron spin can be controlled electrically just with the application of few volts.

3.3 STEPS FOR DETECTING CANCER CELLS USING SPINTRONIC

SCANNER

This spintronic scanning technique is an efficient technique to detect cancer cells even

when they are less in number.

The steps involved are,

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

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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

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

(i) Polarized electron source

(ii) Magnetic field

(iii) Spin detector

3.4 POLARISED 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:

(i) Photoemission from negative electron affinity GaAs

(ii) Chemi-ionization of optically pumped meta stable Helium

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(iii) An optically pumped electron spin filter

(iv) 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.

3.4.1 OPTICAL SPIN FILTER

An optically pumped electron spin filter is a new kind of polarized electron source.

Polarized electrons are an indispensable probe of spin-dependent phenomena in many

areas of physics , but they are difficult to produce.

Fig 3.1 spin filter

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1) dc-discharge cold cathode; (2) discharge anode; (3) discharge high-voltage feed

through; (4) electrically isolated field plate and exit aperture; (5) Rb ampoule; (6) optical

pumping radiation. A magnetic field is applied to the entire apparatus

The figure shows the apparatus for achieving significant electron polarization with

modest N2 and Rb densities. It consists of a 2.75” Conflat® nipple with a glass window

at one end, attached to a noble gas optical electron polarimeter at the other. As an

electron source, two coaxial electrodes are used to maintain a cold-cathode discharge.

The outer anode is generally held at ground, with the cathode at several hundred volts.

The intense, light emitting part of the discharge is ring shaped and is well localized

between the electrodes. The laser pump beam enters through the window, passes through

the electrodes and discharge ring, and is partially reflected by a copper extraction

aperture that is also electrically isolated. A longitudinal electric field of ~20 V/cm

established between the cathode and the extraction aperture drives the free electrons

through the Rb/buffer mixture. As with the test cell, nRb can be controlled by heating the

source chamber. Nitrogen is admitted from a side port. The laser probe beam enters

through the window and passes through the extraction aperture and the optical

polarimeter before being detected by a photodiode. During use, the source tube is heated

to ~100 0 C. Under standard operating conditions, a 5gRb ampoule lasts two or three

weeks. A longitudinal field of up to 600 G is applied to the source and the entrance to the

polarimeter. The polarimeter chamber is made of Pyrex and is pumped with a 1000 l/s

diffusion pump which maintains the vacuum below 10-4 Torr. Electrons extracted from

the source are guided to a region where they collisionally excite an effusive neon target.

The Stokes parameters of radiation from the Ne 2p53p3D3 state are measured with

an optical polarimeter, which views the collision region through the side of the chamber.

The Stokes parameters can then be used to determine the electron polarization. The

extracted electron currents are larger and more stable when the N2 pressure is kept quite

low.

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3.5 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:

i) Mott polarimeter

ii) Compton polarimeter

iii) Moller type polarimeter

Typical Mott polarimeters require electron energies of ~100 keV. But Mini Mott

polarimeter uses energies of ~25 keV, requiring a smaller overall design. The Mini Mott

polarimeter 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 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 chamber and are collected in the detectors.

Thus there are many methods for detecting the spin polarization of electrons.

3.5.1 A Mott Polarimeter

Spin can be detected in a double scattering experiment in which a beam of high energy,

unpolarized electrons are scattered from a high-Z nucleus.

3.5.1.1 Principles of Mott Scattering

As the single electron scattering from a bare, high-Z nucleus passes through the electric

field of the nucleus, a magnetic field is produced in the reference frame of the electron.

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Fig 3.2 Mott Scattering

There are two forces that act on the electron as it approaches the Au nucleus, one due to

the magnetic field and one due to the electric field. Because the electron has a spin

angular momentum, the force exerted by the magnetic field depends on whether the

electron scatters to the left or right.

If the potential scattering curves are plotted for the electron, the curves become skewed

one way or the other depending on the electron’s spin. This leads to an asymmetry in the

left/right scattering probabilities:

where IL and IR are the currents detected in the left and right channels of the polarimeter.

Another important parameter in discussing Mott polarimeters is the figure of merit:

where Io is the current entering the polarimeter, I is the total scattered current, and Seff2 is

the analyzing power of the apparatus:

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where Pe is the degree of electron polarization.

3.5.1.2 Design Aspects of Polarimeter

The designed polarimeter 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 Einsel lens configuration was used here. Two sets of four deflectors were

used as the first and last lens element in this system.

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. Careful consideration must also be employed in choosing the

material. Low-Z nuclei help minimize unwanted scattering, so aluminum was chosen.

Scattered electrons then exit the target chamber and are collected in the detectors. The

target is shown in red and the inner hemisphere in orange.

A simple filament and aperture produce a small beam of electrons. The deflectors in the

transport system were used to raster the beam across the opening to the target chamber.

Current was then measured on the target. This is shown schematically below. The

background current is due to electrons scattered upstream of the target.

Fig 3.4 Schematic view of Polarimeter

Polarized electrons are an indispensable probe of spin-dependent phenomena in many

areas of physics , but they are difficult to produce. State-of-the-art sources of polarized

electrons use either photoemission from negative-electron-affinity GaAs (or variants of

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its basic structure) or chemi-ionization of optically pumped metastable He.

Fig 3.5 graph of upstream Deflectors

Fig 3.6 graph of downstream Deflectors

Both of these methods can yield average currents on the order of 100 mA with

polarizations in excess of 70%. Unfortunately, such sources are technically and

operationally complex.

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3.6 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.

3.7 THE SPINTRONIC SCANNER EXPERIMENTAL SETUP:

Fig 3.7 The spintronic scanner experimental setup

The procedure for doing this experiment is as follows:

i) After surgery and the removal of the tumor, the patient is exposed to a strong

magnetic field.

ii) Now the polarized electron beam is applied over the unaffected part and spin

orientation of electrons are determined using polarimeter.

iii) Then the same polarized beam is targeted over the affected part of the body and from

the reflected beam, change in spin is determined.

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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 this method is suggested for the detection

purpose. A detailed view of this approach is given as follows.

3.8 SPIN ORIENTATION OF THE UNAFFECTED PART OF THE

BODY:

3.8.1 APPLYING MAGNETIC FIELD:

Fig 3.8 Applying magnetic field to the unaffected part of the body

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.

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3.8.2 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.

Fig 3.9 Spin orientation of unaffected part of the body

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3.9 SPIN ORIENTATION OF SURGERY UNDERGONE PART OF THE

BODY:

3.9.1 APPLYING MAGNETIC FIELD:

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.

Fig 3.10 Applying magnetic field to surgery undergone part of the body

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3.9.2 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 are 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.

Fig 3.11 Spin orientation surgery undergone part of the body

3.10 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.

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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.

3.11 ADVANTAGES

The various advantages of Spintronics are as follows:

Spintronics does not require unique and specialised semiconductors, therefore it

can be implemented or worked with common metals, such as Copper, Aluminium

and Silver.

Spintronics devices would consume less power compared to conventional

electronics, because the energy needed to change spin is a easy compared to

energy needed to push charge around.

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

volatile.

The peculiar nature of spin and quantum theory describes it point to other

wonderful possibility like various logic gates whose function can be changed

billion times per second.

Avoiding energy loss or dissipation at room temperature:

So far, only superconductors were known to carry current without any dissipation,

which was possible only at extremely low temperatures, typically -150 degree

Celsius. And due this characteristic they could not be used in commercial devices.

But by modifying electron`s spin property with a sensitive spin detector,

dissipationless spin current could be made to flow even at room temperature.

With lack of dissipation, spintronics may be the best mechanism for creating ever-

smaller devices. With lack of dissipation, spintronics may be the best mechanism

for creating ever-smaller devices.

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3.12 DISADVANTAGES

There will be interference of fields with the nearest element.

Suppose individual memory elements are addressed by flipping their spins up or down to

yield the zeros and ones of binary computer logic. In that case, the common strategy of

running current pulses through wires to induce magnetic fields to rotate the elements is

flawed. This may happen because the fringe fields that are generated may interfere with

neighboring elements.

3.13 CONCLUSION

With lack of dissipation, spintronics may be the best mechanism for creating ever-smaller

devices. Spin can be easily manipulated by externally applied magnetic fields. Another

property of spin is its long coherence, or relaxation, time—once created it tends to stay

that way for a long time, unlike charge states, which are easily destroyed by scattering or

collision with defects, impurities or other charges. The Spintronic scanner is used in

MEDICAL FIELD for the detection of cancer cells even when they are very few in

number in the human body.

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

undergone part, 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, 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.

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3.14REFERENCES

V. M. Novotortsev and V. T. Kalinnikovb., November 2004, Spintronics and

spintronics materials - Russian Chemical Bulletin., Vol. 53, No. 11 (pg. 2357—

2405).

Zutic, Fabian, and Das Sarma., APRIL 2004, Spintronics: Fundamentals and

applications - Reviews of Modern Physics, Vol.76, No.9, (pg. 323-382)

Janice Gabriel., 2004 , Whurr Publishers Ltd., The Biology of Cancer. (Pg. 3-

11, 96-110)

H. Batelaan, A. S. Green., 24 MAY 1999., Optically Pumped Electron Spin

Filter., Vol 82, No.21, (Pg 4216-4219) .

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