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computer science crazy
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21-09-2008, 10:46 AM

Spintronics can be fairly new term for you but the concept isn't so very exotic .This technological discipline aim to exploit subtle and mind bending esoteric quantum property of electron to develop a new generation of electronics devices. The ability to exploit spin in semiconductor promise a new logical devices as spin transistor etc with enhanced functionality higher speed and reduction power conception and might have a spark revolution in semiconductor industry. so far the problem of injecting electron with controlled spin direction has held up the realization of such spintronics

Spintronics is an emergent technology that exploits the quantum propensity of the electrons to spin as well as making use of their charge state. The spin itself is manifested as a detectable weak magnetic energy state characterised as "spin up" or "spin down".

Conventional electronic devices rely on the transport of electrical charge carriers - electrons - in a semiconductor such as silicon. Device engineers and physicists are now trying to exploit the spin of the electron rather than its charge.
Spintronic-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. Spintronic-devices are playing an increasingly significant role in high-density data storage, microelectronics, sensors, quantum computing and bio-medical applications, etc.
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05-04-2010, 10:56 AM

.ppt   Introduction-to-Spintronics.ppt (Size: 1.55 MB / Downloads: 465)
Introduction to Spintronics
Electron has : Mass Charge Spin Spintronics=spin based electronics information is carried by spin not by

charge ferromagnetic metallic alloy based devices transport in fm materials is spin polarized

Conventional electronic devices ignore the spin property

As electronic devices become smaller, quantum properties of the wavelike nature of electrons are no longer


Adding the spin degree of freedom provides new effects, new capabilities and new functionalities

Information is stored into spin as one of two possible orientations
Advantages of spintronics

Non-volatile memory
performance improves with smaller devices
Low power consumption
Spintronics does not require unique and specialised semiconductors
Dissipation less transmission
Switching time is very less
compared to normal RAM chips, spintronic RAM chips will:
“ increase storage densities by a factor of three
“ have faster switching and rewritability rates smaller

Phases in Spintronics



Spin injection
Using a ferromagnetic electrode

effective fields caused by spin-orbit interaction.

a vacuum tunnel barrier could be used to effectively inject spins into a semiconductor

back biased Fe/AlGaAs Schottky diode has been reported to yield a spin injection efficiency of 30%

By hot electrons
Spin Transfer
Current passed through a magnetic field becomes spin polarized

This flipping of magnetic spins applies a relatively large torque to the magnetization within the external


This torque will pump energy to the magnet causing its magnetic moment to precess

If damping force is too small, the current spin momentum will transfer to the nanomagnet, causing the

magnetization to flip

Spin detection

Optical detection techniques using magnetic resonance force microscopy

Electrical sensing techniques-through quantum dots and quantum point contact


Leads to spin equilibration

T1-Spin-lattice relaxation time

T2-Spin-spin relaxation time

Neccesary condition 2T1>=T2.
Application GMR(Giant magnetoresistance)
Discovered in 1988 France

a multilayer GMR consists of two or more ferromagnetic layers separated by a very thin (about 1 nm) non-

ferromagnetic spacer (e.g. Fe/Cr/Fe)

When the magnetization of the two outside layers is aligned, resistance is low

Conversely when magnetization vectors are antiparallel, high R

Spin Valve

Simplest and most successful spintronic device
Used in HDD to read information in the form of small magnetic fields above the disk surface

Tunnel Magnetoresistance

Tunnel Magnetoresistive effect combines the two spin channels in the ferromagnetic materials and the quantum

tunnel effect

TMR junctions have resistance ratio of about 70%
MgO barrier junctions have produced 230% MR


MRAM uses magnetic storage elements

Tunnel junctions are used to read the information stored in MRAM


Attempts were made to control bit writing by using relatively large currents to produce fields
This proves unpractical at nanoscale level
The spin transfer mechanism can be used to write to the magnetic memory cells
Currents are about the same as read currents, requiring much less energy

MRAM promises:
Density of DRAM
Speed of SRAM
Non-volatility like flash

Spin Transistor
Ideal use of MRAM would utilize control of the spin channels of the current
Spin transistors would allow control of the spin current in the same manner that conventional transistors can

switch charge currents
Using arrays of these spin transistors, MRAM will combine storage, detection, logic and communication

capabilities on a single chip
This will remove the distinction between working memory and storage, combining functionality of many devices

into one
Datta Das Spin Transistor
The Datta Das Spin Transistor was first spin device proposed for metal-oxide geometry, 1989
Emitter and collector are ferromagnetic with parallel magnetizations
The gate provides magnetic field
Current is modulated by the degree of precession in electron spin
Current Research
Ferromagnetic transition temperature in excess of 100 K
Spin injection from ferromagnetic to non-magnetic semiconductors and long spin-coherence times in


Ferromagnetism in Mn doped group IV semiconductors.
Room temperature ferromagnetism
Large magnetoresistance in ferromagnetic semiconductor tunnel junctions.
Future Outlook
High capacity hard drives
Magnetic RAM chips
Spin FET using quantum tunneling
Quantum computers


Controlling spin for long distances
Difficult to INJECT and MEASURE spin.
Interfernce of fields with nearest elements
Control of spin in silicon is difficult

please read

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12-03-2011, 11:29 AM


.pptx   spintronics ppt.pptx (Size: 128.56 KB / Downloads: 105)
One of the tiniest particles in the universe, long appreciated as an amazing carrier of electrical charge, now discovered to be even more capable .It spins.
What Is Spintronics ? ? ?
Spintronics ("spin transport electronics"), also known as magnetoelectronics, is an emerging technology that exploits the intrinsic spin of the electron and its associated magnetic moment, in addition to its fundamental electronic charge, in solid-state devices.
The storage and transfer of information using the spin state of electrons as well as their charge.
1988 - Giant Magnetoresistive Effect (GME) discovered by Albert Fert.
2004 - IBM scientists view a single electron spin with a special atomic force microscope.
2005-July - New Spintronic Speed Record - 2GHz MRAM devised.
2009March –Scientists prove that the existence of a spin battery.
2011-January – researches manage to generate spin current in graphene
From 1980 to 2011
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07-04-2011, 02:11 PM

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.pptx   spintronics_ppt.pptx (Size: 378.22 KB / Downloads: 72)

 Spintronics, also known as magnetoelectronics, exploits the intrinsic spin of the electron.
 They rely completely on magnetic moment of the electron.
 Electrons are spin-1/2 fermions and therefore constitute a two-state system with spin "up" and spin "down".
 Electrons have a property that they occupy only one quantum state at a given time.
 To make a spintronic device, the primary requirements are a system that can generate a current of spin-polarized electrons comprising more of one spin species—up or down—than the other (called a spin injector),
 Spin process can be accomplished using real external magnetic fields or effective fields caused by spin-orbit interaction.
 The research field of spintronics emerged from experiments on spin-dependent electron transport phenomena in solid-state devices done in the 1980s.
 Further in 1997 this technology got a boost by the discovery of Giant magnetoresistance (GMR) .
 GMR was discovered by Albert Fert and Peter Grünberg for which they also got nobel prize in physics.
All spintronic devices act according to the simple scheme:
(1) Information is stored (written) into spins as a particular spin orientation (up or down).
(2) The spins, being attached to mobile electrons, carry the information along a wire, and
(3) The information is read at a terminal.
 GMR is a quantum mechanical magnetoresistance effect observed in thin film structures composed of alternating ferromagnetic and non magnetic layers.
 In GMR two or more ferromagnetic layers are separated by a very thin (about 1 nm) non-ferromagnetic spacer (e.g. Fe/Cr/Fe). At certain thicknesses the coupling between adjacent ferromagnetic layers becomes
Spin detection in semiconductors is another challenge, which has been met with the following techniques:
 Faraday/Kerr rotation of transmitted/reflected photons.
 Circular polarization analysis of electroluminescence.

 To devise economic ways to combine ferromagnetic metals and semiconductors in integrated circuits.
 To find an efficient way to inject spin-polarized currents, or spin currents, into a semiconductor.
 To maximize the time period for spin current to retain its polarization in a semiconductor.
 To make semiconductors that are ferromagnetic at room temperature and don’t lose their property even at high temperature
 To minimize spin currents at boundaries between different semiconductors so as to minimize the loss .
 Motorola has developed a 1st generation 256 kb MRAM based on a single magnetic tunnel junction and a single transistor and which has a read/write cycle of under 50 nanoseconds.
 There are two 2nd generation MRAM techniques currently in development:
a).Thermal Assisted Switching (TAS) which is being developed by Crocus Technology, and
b). Spin Torque Transfer (STT) on which Crocus, Hynix, IBM, and several other companies are working.
 Semiconductor lasers using spin-polarized electrical injection have shown threshold current reduction and controllable circularly polarized coherent light output.
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11-05-2011, 09:45 AM

.ppt   Spintronics.ppt (Size: 761 KB / Downloads: 79)
Measurable Performance Objectives
Students will understand the difference between classic and quantum mechanics
Students will acquire basic understanding of quantum mechanics
Students will demonstrate the knowledge of spintronics
Students will be able to define qubit
Students will be able to compare conventional microelectronic and spintronic devices
Students will gain an insight into future technology
Students will be able to design a top of the technology computer.
Opening discussion Computer Technology….. then and now
Storage devices
Hard drive storage capacity
Limiting factors
Internet access
Paper and pencil
Concepts, Principles, and Facts
Classic vs. quantum mechanics
Introduction to quantum mechanics
Spin-based electronics or spintronics
Conventional microelectronic vs. spintronic devices
Future technology
Available commercial products.
Classic vs. quantum mechanics
Macro world vs. the nano world
What is quantum mechanics?
Why do we need quantum mechanics?
Measurements in the macro vs nano world
Quantum Mechanics offers explanation for
Discrete energy levels
The theory of wave-particle dual nature
Quantum tunneling
The Heisenberg uncertainty principle
Spin of a particle
Spin-based electronics
Charge-based electronics vs. spin-based electronics
Advantages of spin-based electronics
Spintronics storage devices
Define qubit
Bit vs. qubit
Representation of a qubit with bra-ket notation, |o>, |1> and superposition of the two
Spintronics products
Hard drives up to 1.2 petabytes
Spintronics products
iPod nano
Cell phones
Laptop hard drives
Future Outlook
High capacity hard drives
Magnetic RAM chips
Spin FET using quantum tunneling
Commercial products
Hard drives
Other devices
400 GB Hard Drive
External 400GB Hard Drive (USB 2.0/FireWire, 7200 RPM, 8MB) $300.00   Manufacturer: Seagate Model: ST3400801CBRK Interface: IEEE 1394 (Firewire)|USB - Universal Serial Bus 2.0 Access Time: 8.5 Rotational Speed: 7200  PRODUCT INFO External 400GB Hard Drive
4GB Flash drive
4GB Compact Flash card
4GB flash drive which can even hold 8GB data with 2:1 data compression.
At a cost of $1699.95 you can get
one Apple PowerBook 12“
Six Apple iPod Mini 4GB
Nine 1GB Hi-Speed USB flash drives.
A project and implimentation will be assigned to design a top of the technology computer with bill of material. The students will present their system design to the class using power point presentation.
Evaluation Criteria
Students will demonstrate proficiency on all measurable performance objectives at least to the 75% level. Evaluation will be based on written report and oral presentation. A rubric will be used for evaluation.
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12-05-2011, 12:13 PM

.doc   Copy of PRESENT PROJECT SPINTRONICS _ 123.doc (Size: 1.02 MB / Downloads: 61)

“Spintronics” is an emergent NANOtechnology, which uses the spin of an electron instead of or in addition to the charge of an electron. Electron spin has two states either “up” or “down”. Aligning spins in material creates magnetism. Moreover, magnetic field affects the passage of spin-up and spin-down electrons differently the paper starts with the detail description of the fundamentals and properties of the spin of the electrons. It proceeds with a note on magnetoresistance, the development of Giant Magnetoresistance (GMR) and devices like Magneto Random Access Memory, which are the new version of the traditional RAMs. It describe how this new version of RAMs which can revolutionize the memory industry. There is also detailed explanation of the way, how this revolution can increase the data density in our memory systems. It is followed by an account of new Spin Field Effect Transistors. It also specifies the differences between electronic devices and spintronic devices. It also gives the hurdles due to the presence of holes.
This paper also discusses about a quantum computer, which uses qubits rather than normal binary digits for computations. It also gives the hurdles due to the presence of holes.
Finally it ends with a note on why we should switch on this technology. Ran road track and conveyor belts kept the Ford’s assemble line running. At that time, his method of production was lauded and was considered most efficient. But that ford’s assembly plant, which was only eulogized in his time, will look strange to those who were born and raised up in the 21st century. Because the machines in the next 50 years will get increasingly smaller – so small that thousands of machines will fit into the full stop at the end of this line. This branch of engineering which deals with things smaller than 100 nanometres is termed as NANOtechnology. Eric Dexler first coined it in his book “engine of creation”.
In this paper we will discuss about a filed of Nanotechnology, which is believed to replace conventional electronics in the near future, i.e. “spintronics”.
History of Nanotechnology:
As nanoscience has advanced and discoveries in the field applied, the potential contributions of nanotechnology to future economic growth has brought increasing government attention. Today, nanotechnology is a top research priority of the Bush administration.
Attempts to coordinate federal work on the nanoscale began in November 1996, when staff members from several agencies decided to meet regularly to discuss their plans and programs in nanoscale science and technology. This group continued informally until September 1998, when it was designated as the Interagency Working Group on Nanotechnology (IWGN) under the National Science and Technology Council (NSTC).
The IWGN sponsored numerous workshops and studies to define the state of the art in nanoscale science and technology and to forecast possible future developments. Two relevant background publications were produced by the group between July and September 1999: Nanostructure Science and Technology: A Worldwide Study, a report based on the findings of an expert panel that visited nanoscale science and technology laboratories around the world; and Nanotechnology Research Directions, a workshop report with input from academic, private sector, and government participants. These documents laid the groundwork and provided the justification for seeking to raise nanoscale science and technology to the level of a national initiative.
In August 1999, IGWN completed its first draft of a plan for an initiative in nanoscale science and technology. The plan went through an approval process involving the President's Council of Advisors on Science and Technology (PCAST) and the Office of Science and Technology Policy . Subsequently, in its 2001 budget submission to Congress, the Clinton administration raised nanoscale science and technology to the level of a federal initiative, officially referring to it as the National Nanotechnology Initiative (NNI).
The National Nanotechnology Coordination Office (NNCO) was established to serve as the secretariat for the NSET, providing day-to-day technical and administrative support. The NNCO supports the NSET in multiagency planning and the preparation of budgets and program assessment documents. It also assists the NSET with the collection and dissemination of information on industry, state, and international nanoscale science and technology research, development, and commercialization activities. The importance of a coordinated Federal program for nanotechnology R&D was given greater recognition in 2003 with the enactment of the 21st Century Nanotechnology Research and Development Act (Public Law 108-153).
A common thread between store age, medical, industrial & molecular
Nanotechnology is an exponential curve.
The goal of early nanotechnology is to produce the first nano-sized robot arm capable of manipulating atoms and molecules into a useful producer copies of itself. Nano assembler working atom by atom would be rather slow because most desirable products are made of billions & trillions of atoms. However, an assembler robotarm could make copies of itself and those copies make copies. Then we have trillions of assemblers controlled by nano-super computers working in parallel assembling objects quickly.
What is Nanotechnology ???
Nanotechnology is the understanding and control of matter at dimensions of roughly 1 to 100 nanometers, where unique phenomena enable novel applications. Encompassing nanoscale science, engineering and technology, nanotechnology involves imaging, measuring, modeling, and manipulating matter at this length scale.
At the nanoscale, the physical, chemical, and biological properties of materials differ in fundamental and valuable ways from the properties of individual atoms and molecules or bulk matter. Nanotechnology R&D is directed toward understanding and creating improved materials, devices, and systems that exploit these new properties.
One area of nanotechnology R&D is medicine. Medical researchers work at the micro- and nano-scales to develop new drug delivery methods, therapeutics and pharmaceuticals. For a bit of perspective, the diameter of DNA, our genetic material, is in the 2.5 nanometer range, while red blood cells are approximately 2.5 micrometers. Additional information about nanoscale research in medicine is available from the National Institutes of Health. A nanometer is one-billionth of a meter; a sheet of paper is about 100,000 nanometers thick. See The Scale of Things for a comparative view of the sizes of commonly known items and nanoscale particles.
Imagine a data storage device of the size of an atom working at a speed of light. Imagine a microprocessor whose circuits could be changed on the fly. One minute is could be optimized for data base access. The next for transaction processing and the next for scientific number crunching. Finally, imagine a computer memory thousands of times denser and faster than today’s memories.
The above-mentioned things can be made possible with the help of an exploding science – “spintronics”.
Spintronics is a NANO technology which deals with spin dependent properties of an electron instead of or in addition to its charge dependent properties,.
Conventional electronics devices rely on the transport of electric charge carries-electrons. But there is other dimensions of an electron other than its charge and mass i.e. spin. This dimension can be exploited to create a remarkable generation of spintronic devices. It is believed that in the near future spintronics could be more revolutionary than any other thing that nanotechnology has stirred up so far.
As there is rapid progress in the miniaturization of semiconductor electronic devices leads to a chip features smaller than 100 nanometers in size, device engineers and physists are inevitable faced with a looming presence of a quantum property of an electron known as spin, which is closely related to magnetism. Devices that rely on an electron spin to perform their functions from the foundations of spintronics.
Information-processing technology has thus far relied on purely charge based devices ranging from the now quantum, vaccum tube today’s million transistor microchips. Those conventional electronic devices move electronic charges around, ignoring the spin that tags along that side on each electron.

1. In addition to their mass and electric charge, 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 “down” for the opposite spin.
4. In a magnetic field, electrons with “spin up” and “spin down” have different energies.
5. In an ordinary electronic circuit the spins are oriented at random and have no effect on current flow.
6. Spintronic devices create spin-polarized currents and use the spin to control current flow.
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09-07-2011, 04:49 PM

.docx   spintronics - main.docx (Size: 1.14 MB / Downloads: 59)
Semiconductor spintronics

Conventional electronics rely upon and utilize the flow of an electron’s charge. The idea of Spintronics involves utilizing an electron’s spin as well. In addition to an electron’s orbital angular momentum, an electron has an intrinsic angular momentum called its spin angular momentum. This is simply known as spin, and it can be denoted by the vector S. Other elementary particles, such as protons, also have spin. This spin is associated with a particle’s intrinsic spin magnetic dipole moment, sμ. The vector Sand the moment sμ, are related in the following way:
Where e is the elementary charge and m is the mass of an electron. Now, S cannot be measured directly; however its component along any axis can be measured.In a narrow sense spintronics refers to spin electronics, the phenomena of spin-polarized transport in metals and semiconductors. The goal of this applied spintronics is to find effective ways of controlling electronic properties, such as the current or accumulated charge, by spin or magnetic field, as well as of controlling spin or magnetic properties by electric currents or gate voltages. The ultimate goal is to make practical device schemes that would enhance functionalities of the current charge-based electronics. An example is a spin field-effect transistor, which would change its logic state from ON to OFF by flipping the orientation of a magnetic field.
In a broad sense spintronics is a study of spin phenomena in solids, in particular metals and semiconductors and semiconductor heterostructures. Such studies characterize electrical, optical, and magnetic properties of solids due to the presence of equilibrium and nonequilibrium spin populations, as well as spin dynamics. These fundamental aspects of spintronics give us important insights about the nature of spin interactions—spin-orbit, hyperfine, or spin exchange couplings—in solids. We also learn about the microscopic processes leading to spin relaxation and spin dephasing, microscopic mechanisms of magnetic long-range order in semiconductor systems, topological aspects of mesoscopic spin-polarized current flow in low-dimensional semiconductor systems, or about the important role of the electronic band structure in spin-polarized tunneling, to name a few.
Spintronics refers commonly to phenomena in which the spin of electrons in a solid state environment plays the determining role. In a more narrow sense spintronics is an emerging research field of electronics: spintronics devices are based on a spin control of electronics, or on an electrical and optical control of spin or magnetism. While metal spintronics has already found its niche in the computer industry—giant magnetoresistance systems are used as hard disk read heads—semiconductor spintronics is yet to demonstrate its full potential. This review presents selected themes of semiconductor spintronics, introducing important concepts in spin transport, spin injection, Silsbee-Johnson spin-charge coupling, and spindependent tunneling, as well as spin relaxation and spin dynamics. The most fundamental spin-dependent interaction in nonmagnetic semiconductors is spin-orbit coupling. Depending on the crystal symmetries of the material, as well as on the structural properties of semiconductor based heterostructures, the spin-orbit coupling takes on different functional forms, giving a nice playground of effective spin-orbit Hamiltonians. The effective Hamiltonians for the most relevant classes of materials and heterostructures are derived here from realistic electronic band structure descriptions. Most semiconductor device systems are still theoretical concepts, waiting for experimental demonstrations. A review of selected proposed, and a few demonstrated devices is presented, with detailed description of two important classes: magnetic resonant tunnel structures and bipolar magnetic diodes and transistors. In view of the importance of ferromagnetic semiconductor materials, a brief discussion of diluted magnetic semiconductors is included. In most cases the presentation is of tutorial style, introducing the essential theoretical formalism at an accessible level, with case-study-like illustrations of actual experimental results, as well as with brief reviews of relevant recent achievements in the field.
Spintronics promises the possibility of integrating memory and logic into a single device. In certain cases, switching times approaching a picosecond are possible, which can greatly increase the efficiency of optical devices such as light-emitting diodes (LEDs) and lasers. The control of spin is central as well to efforts to create entirely new ways of computing, such as quantum computing, or analog computing that uses the phases of signals for computations. Spin is a fundamental quantum-mechanical property. It is the intrinsic angular momentum of an elementary particle, such as the electron. Of course, any charged object possessing spin also possesses an intrinsic magnetic moment. It has been known for decades that in ferromagnetism the spins of electrons are preferentially aligned in one direction. Then, in 1988, it was demonstrated that currents flowing from a ferromagnet into an ordinary metal retain their spin alignment for distances longer than interatomic spaces, so that spin and its associated magnetic moment can be transported just as charge. This means that magnetization as well can be transferred from one place to another.

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