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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