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SPINTRONICS The Technology of Future…!

Edited By: Priyabrata Nayak

Lecturer, Dept. of CSE



Why Spintronics?

What is Spintronics?

Principle

Fabrication & Working of spin devices

Electronics Vs. Spintronics

Applications

Conclusion

The Future Belongs To Spintronics

OUTLINE



Why Spintronics?Moore’s Law:

No. of Transistor doubles in every 18 months

Complexity:

Complex Chip Design & Power Loss

Motivation:

Spintronics-Information is carried not byelectron charge but by it’s spin.



What is Spintronics?Spintronics is a blend of electronics withspin.

It refers to the study of the role played bythe electron spin in solid state physics andpossible devices that specifically exploitsspin properties of electrons instead of it’s

charge.It promises new logic devices whichenhances functionality, high speed andreduced power consumption.



PrincipleSpintronics is based on the spin of electronsrather than its charge.

Every electron exist in one of the two states-spin-up and spin-down, with spins either positive half or negative half.In other words, electrons can rotate either clockwise or anti-clockwise around its own axis withconstant frequency.The two possible spin states represent ‘0’ and ‘1’ in logical operations.



PrincipleSpin is a characteristic that makes an electron atiny magnet with north and south poles.

The orientation of north-south axis depends onthe particle’s axis of spin.In ordinary materials, the up magneticmoments cancel the down magnetic momentso no surplus moment piles up.Ferro-magnetic materials like iron, cobalt andnickel is needed for designing of spinelectronic devices.



PrincipleThese have tiny regions called domains inwhich an excess of electrons have spins with

axis pointing either up or down.The domains are randomly scattered andevenly divided between majority-up andmajority-down.But, an externally applied magnetic field willline up the domains in the direction of thefield. This results in a permanent magnet.



PrincipleWhen a pool of spin-polarized electrons is putin a magnetic field, precession occurs.

The frequency and direction of rotationdepends on the strength of magnetic field andcharacteristics of the material.Thus, if a voltage pushes an electron out of gallium arsenide into zinc selenide, theelectron precession characteristics change.However, if a higher voltage pushes theelectron sharply into zinc selenide, theelectron precession characteristics don’t

change.



PrincipleN-type materials rely on electrons to carrycurrent where as P-type materials rely onholes.

As the materials are of two different carrier types, an electric field is formed around their

junction.This field is strong enough to pull a pool of

spin coherent electrons from GaAsimmediately into ZnSe, where coherencepersist for 100 of nanoseconds.Thus, spin can be moved from one kind of semiconductor to another without the need for external electric fields.



FabricationSpintronics devices involves two differentapproaches for designing & manufacturing.

Perfecting the existing giant magneto resistance,GMR based technology by developing newmaterials with larger spin polarization.

Finding the novel ways of both generation and

utilization of spin polarized current.The later one is a effective method.



WorkingAll spintronic devices acts according to thesimple scheme: The information is stored(written) into spins as a particular spin

orientation (up or down).The spins, being attached to mobile electrons,carry information along a wire and theinformation is read at a terminal.

Spin orientation of conduction electronssurvives for relatively long time (nanoseconds,compared to tens of femtoseconds duringwhich electron moment decays) which makesspintronic device useful for memory storage

and magnetic sensor applications.



Working

These are used for quantum computing whereelectron spin will represent a bit (called ‘qubit’) of information.When electron spins are alligned, this creates alarge scale net magnetic moment.The basic GMR device is a 3 layer sandwich of magnetic metal (such as cobalt) with a non-

magnetic metal filling (such as silver).A current passes through the layers consistingof spin up and spin down electrons.



The electrons oriented in the same direction as the electron spin in themagnetic layer pass through quite easily while those oriented in theopposite direction are scattered.If orientation of one of the magnetic layers is changed by the presence of amagnetic field, the device will act as a filter or a spin valve letting throughmore electrons when spin orientation in the two layers are the same and

fewer electrons when spin orientation are oppositely alligned.



The electrical resistance of the device can therefore be changeddramatically.The above diagram depicts the nature of the spin valve when the twolayers are oppositely alligned.



Electronics vs. Sprintronics

One of the main advantage of spintronics over electronics is the magnets tend to stay

magnetize which is sparking in the industry aninterest for replacing computer’s semiconductor based components withmagnetic ones, starting with the RAM.

With an all-magnetic RAM, it is now possible

to have a computer that retains all theinformation put into it. Most importantly,there will be no ‘boot-up’ waiting period whenpower is turned on.




Another promising feature of spintronicsis that it doesn’t require the use of

unique and specialized semiconductor,there by allowing it to work withcommon metals like Cu, Al, Ag.

Spintronics will use less power than

conventional electronics, because theenergy needed to change spin is a minutefraction of what is needed to push chargearound.




Another advantage includes Non-volatility: Spins don’t change when

power is turned off. The peculiar nature of spin and quantum

theory describes it point to other wonderful possibility like various logic

gates whose function can be changedbillion times per second.



Application

The Magnetic version of RAM used incomputer is nonvolatile.

Other advantages of MRAM’s include smallsize, lower cost, faster speed and less power consumption, robust in extreme conditionsuch as high temperature, high level

radiation and interference.



Applications

Magnetic RAM



Applications

GMR sensors find a wide range of applications: Fast and accurate position and motion sensing

of mechanical components in precisionengineering and robotics. Missile Guidance Position and motion sensing in computer video

games. Key Hole Surgery and post operative care. Automotive sensors for fuel handling system,

speed control and navigation etc.



Applications

Spin Valve Transistors:It is based on magnetoresistance, found in multi

layers (Co-Cu-Co) formingthe base region.The collector currentbecomes strongly fielddependent, the extreme

magneto sensitivity makesthe transistor, an interestingdevice for high technologyhard disks and magneticRAMs.



Conclusion

With lack of dissipation, spintronics may be

the best mechanism for creating ever-smaller devices. The potential market is enormous, Inmaybe a 10-year timeframe, spintronics willbe on par with electronics. That's why there's

a huge race going on around the world Inexploring Spintronics.




Any Queries…?



Thank you all


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