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| | My name is Maurine and I am studying International Relations and Political Science at Shelfield / Great Britain.<br><br>Check out my page; [http://www.celebritynetworth.com/dl/arthur-falcone/ Arthur Falcone] |
| '''Spintronics''' (a [[portmanteau]] meaning "spin transport electronics"<ref>{{cite doi|10.1147/rd.501.0101}}</ref><ref>[http://video.google.com/videoplay?docid=2927943907685656536&q=LevyResearch&ei=dxd1SNCtOqj2rAKxzf1p Physics Profile: "Stu Wolf: True D! Hollywood Story"]{{dead link|date=October 2013}}</ref><ref>[http://www.sciencemag.org/content/294/5546/1488.short Spintronics: A Spin-Based Electronics Vision for the Future]. Sciencemag.org (16 November 2001). Retrieved on 21 October 2013.</ref>), also known as '''spinelectronics''' or '''fluxtronic''', is an [[emerging technology]] exploiting both the intrinsic [[spin (physics)|spin]] of the [[electron]] and its associated [[magnetic moment]], in addition to its fundamental electronic charge, in [[Solid state (electronics)|solid-state devices]].
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| Spintronics differs from the older [[magnetoelectronics]], in that the spins are not only manipulated by [[magnetic field]]s, but also by [[electric field|electrical fields]].
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| ==History==
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| Spintronics emerged from discoveries in the 1980s concerning spin-dependent electron transport phenomena in solid-state devices. This includes the observation of spin-polarized electron injection from a ferromagnetic metal to a normal metal by Johnson and Silsbee (1985),<ref>{{cite doi|10.1103/PhysRevLett.55.1790}}</ref> and the discovery of [[giant magnetoresistance]] independently by [[Albert Fert]] et al.<ref>{{cite doi|10.1103/PhysRevLett.61.2472}}</ref> and [[Peter Grünberg]] et al. (1988).<ref>{{cite doi|10.1103/PhysRevB.39.4828}}</ref> The origins of spintronics can be traced back even further to the ferromagnet/superconductor tunneling experiments pioneered by Meservey and Tedrow, and initial experiments on magnetic tunnel junctions by Julliere in the 1970s.<ref>{{cite doi|10.1016/0375-9601(75)90174-7}}</ref> The use of semiconductors for spintronics can be traced back at least as far as the theoretical proposal of a spin field-effect-transistor by [[Supriyo Datta|Datta]] and Das in 1990.<ref>{{cite journal| doi = 10.1063/1.102730| author = Datta, S. and Das, B. |title = Electronic analog of the electrooptic modulator|journal = Applied Physics Letters| volume = 56| pages = 665–667|year = 1990|bibcode = 1990ApPhL..56..665D| issue = 7 }}</ref>
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| In 2012, [[IBM]] scientists mapped the creation of persistent spin helices of synchronized electrons persisting for more than a nanosecond. This is a 30-fold increase from the previously observed results and is longer than the duration of a modern processor clock cycle, which opens new paths to investigate for using electron spins for information processing.<ref>{{cite journal|author=Walser, M.; Reichl, C.; Wegscheider, W. and Salis, G. |title=Direct mapping of the formation of a persistent spin helix|journal=Nature Physics|doi=10.1038/nphys2383|bibcode = 2012NatPh...8..757W|year=2012|volume=8|issue=10|pages=757 }}</ref>
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| == Theory ==
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| The [[Spin (physics)|spin]] of the electron is an [[angular momentum]] intrinsic to the electron that is separate from the angular momentum due to its orbital motion. The magnitude of the projection of the electron's spin along an arbitrary axis is <math>\frac{1}{2}\hbar</math>, implying that the electron acts as a [[Fermion]] by the [[spin-statistics theorem]]. Like orbital angular momentum, the spin has an associated [[magnetic moment]], the magnitude of which is expressed as
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| :<math>m=\frac{\sqrt{3}}{2}\frac{q}{m_e}\hbar</math>.
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| In a solid the spins of many electrons can act
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| together to affect the magnetic and electronic properties of a material, for example endowing a material with a permanent magnetic moment as in a [[ferromagnet]].
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| In many materials, electron spins are equally present in both the up and the down state, and no transport properties are dependent on spin. A spintronic device requires generation or manipulation of a spin-polarized population of electrons, resulting in an excess of spin up or spin down electrons. The polarization of any spin dependent property X can be written as
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| :<math>P_X=\frac{X_{\uparrow}-X_{\downarrow}}{X_{\uparrow}+X_{\downarrow}}</math>.
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| A net spin polarization can be achieved either through creating an equilibrium energy splitting between spin up and spin down such as putting a material in a large magnetic field ([[Zeeman effect]]) or the exchange energy present in a ferromagnet; or forcing the system out of equilibrium. The period of time that such a non-equilibrium population can be maintained is known as the spin lifetime, <math>\tau</math>. In a diffusive conductor, a [[spin diffusion]] length <math>\lambda</math> can also be defined as the distance over which a non-equilibrium spin population can propagate. Spin lifetimes of conduction electrons in metals are relatively short (typically less than 1 nanosecond), and a great deal of research in the field is devoted to extending this lifetime to technologically relevant timescales.
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| [[File:Spin Injection.jpg|right|thumb|A plot showing a spin up, spin down, and the resulting spin polarized population of electrons. Inside a spin injector, the polarization is constant, while outside the injector, the polarization decays exponentially to zero as the spin up and down populations go to equilibrium.]]
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| There are many mechanisms of decay for a spin polarized population, but they can be broadly classified as spin-flip scattering and spin dephasing. Spin-flip scattering is a process inside a solid that does not conserve spin, and can therefore send an incoming spin up state into an outgoing spin down state. Spin dephasing is the process wherein a population of electrons with a common spin state becomes less polarized over time due to different rates of electron spin precession. In confined structures, spin dephasing can be suppressed, leading to spin lifetimes of milliseconds in semiconductor quantum dots at low temperatures.
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| By studying new materials and decay mechanisms, researchers hope to improve the performance of practical devices as well as study more fundamental problems in condensed matter physics.
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| ==Metal-based spintronic devices==
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| The simplest method of generating a spin-polarised current in a metal is to pass the current through a [[ferromagnetic]] material. The most common applications of this effect involve [[giant magnetoresistive effect|giant magnetoresistance]] (GMR) devices. 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, the electrical resistance will be lower (so a higher current flows at constant voltage) than if the ferromagnetic layers are anti-aligned. This constitutes a magnetic field sensor.
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| Two variants of GMR have been applied in devices: (1) current-in-plane (CIP), where the electric current flows parallel to the layers and (2) current-perpendicular-to-plane (CPP), where the electric current flows in a direction perpendicular to the layers.
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| Other metals-based spintronics devices:
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| * [[Tunnel magnetoresistance]] (TMR), where CPP transport is achieved by using quantum-mechanical tunneling of electrons through a thin insulator separating ferromagnetic layers.
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| * [[Spin-transfer torque]], where a current of spin-polarized electrons is used to control the magnetization direction of ferromagnetic electrodes in the device.
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| * [[Spin-wave logic device]]s utilize the phase to carry information. Interference and spin-wave scattering are utilized to perform logic operations.
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| ==Spintronic-logic devices==
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| Non-volatile spin-logic devices to enable scaling beyond the year 2025<ref>[[International Technology Roadmap for Semiconductors]]</ref> are being extensively studied. Spin-transfer torque-based logic devices that use spins and magnets for information processing have been proposed<ref>{{cite doi|10.1038/nnano.2010.31}}</ref> and are being extensively studied at Intel.<ref>Manipatruni, Sasikanth; Nikonov, Dmitri E. and Young, Ian A. (2011) [http://arxiv.org/abs/1112.2746 [1112.2746] Circuit Theory for SPICE of Spintronic Integrated Circuits]. Arxiv.org. Retrieved on 21 October 2013.</ref> These devices are now part of the ITRS exploratory road map and have potential for inclusion in future computers. Logic-in memory applications are already in the development stage at Crocus<ref>[http://web.archive.org/web/20120420160205/http://crocus-technology.com/pr-12-08-11.html Crocus Partners With Starchip To Develop System-On-Chip Solutions Based on Magnetic-Logic-Unit™ (MLU) Technology]. crocus-technology.com. 8 December 2011</ref> and NEC.<ref>[http://www.nec.com/en/press/201206/global_20120611_02.html Groundbreaking New Technology for Improving the Reliability of Spintronics Logic Integrated Circuits]. Nec.com. 11 June 2012.</ref>
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| ===Applications===
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| [[Disk read-and-write head|Read heads]] of modern [[hard drive]]s are based on the GMR or TMR effect.
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| Motorola has developed a first-generation 256 [[kilobit|kb]] [[magnetoresistive random-access memory]] (MRAM) based on a single magnetic tunnel junction and a single transistor and which has a read/write cycle of under 50 nanoseconds.<ref>[http://www.sigmaaldrich.com/materials-science/alternative-energy-materials/magnetic-materials/tutorial/spintronics.html Spintronics]. Sigma-Aldrich. Retrieved on 21 October 2013.</ref> ([[Everspin]], Motorola's spin-off, has since developed a 4 [[Megabit|Mb]] version<ref>[http://www.everspin.com/technology.php Everspin]. Everspin. Retrieved on 21 October 2013.</ref>). There are two second-generation MRAM techniques currently in development: [[thermal-assisted switching]] (TAS)<ref>Hoberman, Barry. [http://www.crocustechnology.com/pdf/BH%20GSA%20Article.pdf The Emergence of Practical MRAM]. crocustechnology.com </ref> which is being developed by [[Crocus Technology]], and [[spin-transfer torque]] (STT) on which Crocus, [[Hynix]], [[IBM]], and several other companies are working.<ref>LaPedus, Mark (18 June 2009) [http://www.eetimes.com/document.asp?doc_id=1171188 Tower invests in Crocus, tips MRAM foundry deal]. eetimes.com</ref>
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| Another design in development, called [[racetrack memory]], encodes information in the direction of magnetization between domain walls of a ferromagnetic metal wire.
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| There are magnetic [[sensor]]s using the GMR effect.
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| ==Semiconductor-based spintronic devices==
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| Ferromagnetic semiconductor sources (like manganese-doped gallium arsenide [[GaMnAs]]),<ref>{{cite doi|10.1103/PhysRevB.62.8180}}</ref> increase the interface resistance with a tunnel barrier,<ref>{{cite doi|10.1063/1.1449530}}</ref> or using hot-electron injection.<ref>{{cite doi|10.1103/PhysRevLett.90.256603}}</ref>
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| Spin detection in semiconductors is another challenge, met with the following techniques:
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| * Faraday/Kerr rotation of transmitted/reflected photons<ref>{{cite doi|10.1103/PhysRevLett.80.4313}}</ref>
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| * Circular polarization analysis of electroluminescence<ref>Jonker, Berend T. [http://www.patentstorm.us/patents/5874749.html Polarized optical emission due to decay or recombination of spin-polarized injected carriers – US Patent 5874749]. Issued on 23 February 1999.</ref>
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| * Nonlocal spin valve (adapted from Johnson and Silsbee's work with metals)<ref>{{cite doi|10.1038/nphys543}}</ref>
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| * Ballistic spin filtering<ref>{{cite doi|10.1038/nature05803}}</ref>
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| The latter technique was used to overcome the lack of spin-orbit interaction and materials issues to achieve spin transport in [[silicon]], the most important semiconductor for electronics.<ref>{{cite doi|10.1038/447269a}}</ref>
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| Because external magnetic fields (and stray fields from magnetic contacts) can cause large [[Hall effect]]s and [[magnetoresistance]] in semiconductors (which mimic spin-valve effects), the only conclusive evidence of spin transport in semiconductors is demonstration of spin [[precession]] and [[dephasing]] in a magnetic field non-collinear to the injected spin orientation. This is called the [[Hanle effect]].
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| ===Applications===
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| Applications using spin-polarized electrical injection have shown threshold current reduction and controllable circularly polarized coherent light output.<ref>{{cite doi|10.1103/PhysRevLett.98.146603}}</ref> Examples include semiconductor lasers. Future applications may include a spin-based [[transistor]] having advantages over [[MOSFET]] devices such as steeper sub-threshold slope.
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| '''Magnetic-tunnel transistor''': The magnetic-tunnel transistor with a single base layer, by van Dijken et al. and Jiang et al.,<ref name="dijken">{{cite doi|10.1063/1.1474610}}</ref> has the following terminals:
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| * Emitter (FM1): It injects spin-polarized hot electrons into the base.
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| * Base (FM2): Spin-dependent scattering takes place in the base. It also serves as a spin filter.
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| * Collector (GaAs): A [[Schottky barrier]] is formed at the interface. This collector regions only collects electrons when they have enough energy to overcome the Schottky barrier, and when there are states available in the semiconductor.
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| The magnetocurrent (MC) is given as:
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| :<math>MC = \frac{I_{c,p}-I_{c,ap}}{I_{c,ap}}</math>
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| And the transfer ratio (TR) is
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| :<math>TR = \frac{I_C}{I_E}</math>
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| MTT promises a highly spin-polarized electron source at room temperature.
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| == See also ==
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| * [[Magnonics]]
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| * [[Spin pumping]]
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| * [[Spin transfer]]
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| * [[Spinhenge@Home]]
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| * [[Spinplasmonics]]
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| * [[List of emerging technologies]]
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| ==References==
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| {{reflist|35em}}
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| == Further reading ==
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| * "Introduction to Spintronics". Marc Cahay, Supriyo Bandyopadhyay, CRC Press, ISBN 0-8493-3133-1
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| * {{cite journal|title=Ultrafast Manipulation of Electron Spin Coherence|journal=Science|date=29 June 2001|volume=292|issue=5526|pages=2458–2461|doi=10.1126/science.1061169|author=J. A. Gupta, R. Knobel, N. Samarth, D. D. Awschalom|bibcode = 2001Sci...292.2458G|pmid=11431559 }}
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| * {{cite journal|last=Wolf|first=S. A.|title=Spintronics: A Spin-Based Electronics Vision for the Future|journal=Science|date=16 November 2001|volume=294|issue=5546|pages=1488–1495|doi=10.1126/science.1065389|bibcode = 2001Sci...294.1488W|pmid=11711666|first2=DD|first3=RA|first4=JM|first5=S|first6=ML|first7=AY|first8=DM }}
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| * {{cite journal|last=Sharma|first=P.|title=How to Create a Spin Current|journal=Science|date=28 January 2005|volume=307|issue=5709|pages=531–533|doi=10.1126/science.1099388|pmid=15681374}}
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| * "Electron Manipulation and Spin Current". D. Grinevich. 3rd Edition, 2003.*
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| * {{cite doi|10.1103/RevModPhys.76.323}}
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| * {{cite journal |title=SPIN |url=http://www.worldscinet.com/spin/spin.shtml
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| |author=Chief Editor: Parkin, Stuart; Managing Editors: Chang, Ching-Ray & Chantrell, Roy |year=2011 |publisher=World Scientific |issn=2010-3247}}
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| * [http://news.usf.edu/article/templates/?a=4449&z=123 "Spintronics Steps Forward."], [[University of South Florida]] News
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| * {{cite doi|10.1146/annurev-conmatphys-070909-104123}}
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| * {{cite journal |title=Overview of Spintronics |url=http://www.ijert.org/browse/volume-2-2013/june-2013-edition?download=3672%3Aoverview-of-spintronics |author= Mukesh D. Patil, Jitendra S. Pingale, Umar I. Masumdar |year=2013 |publisher=ESRSA Publications |issn=2278-0181}}
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| * {{cite journal |title=Utilization of Spintronics |url=http://www.ijsrp.org/research-paper-0613.php?rp=P181346 |author= Jitendra S. Pingale, Mukesh D. Patil, Umar I. Masumdar |year=2013 |issn=2250-3153}}
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| ==External links==
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| * {{cite journal
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| |url=http://www.sciam.com/article.cfm?articleID=0007A735-759A-1CDD-B4A8809EC588EEDF
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| |title=Spintronics
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| |journal=Scientific American
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| |date=June 2002}}
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| * [http://www.spintronics-info.com/ Spintronics portal with news and resources]
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| * [http://www.informationweek.com/news/internet/showArticle.jhtml?articleID=207200184 RaceTrack:InformationWeek (April 11, 2008)]
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| * [http://www.eetimes.com/news/semi/showArticle.jhtml?articleID=191504070 Spintronics research targets [[GaAs]].]
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| * [http://www.sigmaaldrich.com/materials-science/alternative-energy-materials/magnetic-materials/tutorial/spintronics.html Spintronics Tutorial ]
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| * Lecture on Spin transport by S. Datta (from Datta Das transistor) -[http://nanohub.org/resources/5269 Part 1] and [http://nanohub.org/resources/5270 Part 2]
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| * {{cite journal
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| |url=http://www.ijert.org/browse/volume-2-2013/june-2013-edition?download=3672%3Aoverview-of-spintronics
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| |title=Overview of Spintronics
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| |journal=IJERT
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| |date=June 2013}}
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| * {{cite journal
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| |url=http://www.ijsrp.org/research-paper-0613.php?rp=P181346
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| |title=Utilization of Spintronics
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| |journal=IJSRP
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| |date=June 2013}}
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| {{Emerging technologies}}
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| [[Category:Emerging technologies]]
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| [[Category:Spintronics| ]]
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| [[Category:Theoretical computer science]]
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