Spintronics 61220 225850634 2008-07-15T18:14:53Z Ianappelbaum 7405435 Theory: remove redundant and tangential material; emphasize basic concepts of spin polarization, spintronic device requirements, and spin lifetime '''Spintronics''' (a [[neologism]] meaning "spin transport electronics"<ref>http://www.research.ibm.com/journal/rd/501/wolf.html</ref><ref>http://video.google.com/videoplay?docid=2927943907685656536&q=LevyResearch&ei=dxd1SNCtOqj2rAKxzf1p</ref>), also known as magnetoelectronics, is an emerging [[technology]] which exploits the intrinsic [[spin (physics)|spin]] of [[electron]]s and its associated [[magnetic moment]], in addition to its fundamental electronic charge, in [[Solid state (electronics)|solid-state devices]]. ==History== The research field of Spintronics emerged from seminal experiments on spin-dependent electron transport phenomena in solid-state devices first done in the 1980s, including the observation of spin-polarized electron injection from a ferromagnetic metal to a normal metal by Johnson and Silsbee (1985)<ref>http://prola.aps.org/pdf/PRL/v55/i17/p1790_1</ref>, and the discovery of [[giant magnetoresistance]] independently by [[Albert Fert]] et al.<ref>http://prola.aps.org/abstract/PRL/v61/i21/p2472_1</ref> and [[Peter Grünberg]] et al.<ref>http://prola.aps.org/pdf/PRB/v39/i7/p4828_1</ref> (1988). The origins can be traced back further to the ferromagnet/superconductor tunneling experiments pioneered by Meservey and Tedrow<ref>http://www.met.iitb.ac.in/~ramani/nvree724/refpapers/tedrowspinpolrevu.pdf</ref>, and initial experiments on magnetic tunnel junctions by Julliere in the 1970s<ref>http://www.sciencedirect.com/science/article/B6TVM-46R3N46-10D/2/90703cfc684b0679356dce9a76b2e942</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 Datta and Das in 1990.<ref>http://link.aip.org/link/?APPLAB/56/665/1</ref> ==Theory== Electrons are spin-1/2 [[fermions]] and therefore constitute a two-state system with spin "up" and spin "down". To make a spintronic device, the primary requirements are to have 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), and a separate system that is sensitive to the spin polarization of the electrons (spin detector). Manipulation of the electron spin during transport between injector and detector (especially in semiconductors) via spin [[Precession|precession]] can be accomplished using real external magnetic fields or effective fields caused by [[Spin-orbit_interaction|spin-orbit interaction]]. Spin polarization in non-magnetic materials can be achieved either through the [[Zeeman_effect|Zeeman effect]] in large magnetic fields and low temperatures, or by non-equilibrium methods. In the latter case, the non-equilibrium polarization will decay over a timescale called the "spin lifetime". Spin lifetimes of conduction electrons in metals are relatively short (typically less than 1 [[nanosecond]]) but in semiconductors the lifetimes can be very long ([[Microsecond|microseconds]] at low temperatures), especially when the electrons are isolated in local trapping potentials (for instance, at impurities, where lifetimes can be [[Millisecond|milliseconds]]). ==Applications== Spintronic plates are used in the field of [[mass-storage device]]s; in [[2002]] [[International Business Machines|IBM]] scientists announced that they could compress massive amounts of data into a small area, at approximately one trillion bits per square inch (1.5 Gbit/mm²) or roughly 1 TB on a single sided 3.5" diameter disc. The storage density of [[hard drives]] is rapidly increasing along an exponential growth curve. The doubling period for the areal density of information storage is twelve months, much shorter than [[Moore's Law]], which observes that the number of transistors in an [[integrated circuit]] doubles every twenty-four months. More recently (April 11, 2008), IBM Fellow, Dr. Stuart Parkin, announced next-generation nonvolatile memory dubbed "[[Racetrack memory|RaceTrack]]" which is expected to initially replace flash memory and eventually mechanical magnetic hard-disk drives. The prototype encodes bits into the magnetic domain walls along the length of a silicon nanowire, also known as RaceTrack. This method allows "massless motion" to move the magnetic domain walls along the silicon nanowire for the storage and retrieval of information. Such drives will be able to store data nearing 1 Terabytes on a single 3.5inch (8.9cm) drive. The most successful spintronic device to date is the [[spin valve]], due to their widespread application in disk read/write heads. This device utilizes a layered structure of thin films of magnetic materials which changes electrical resistance depending on the applied magnetic field direction. In a spin valve, one of the ferromagnetic layers is "pinned" so its magnetization direction remains fixed and the other ferromagnetic layer is "free" to rotate with the application of a magnetic field. When the magnetic field aligns the free layer and the pinned layer magnetization vectors, the [[electrical resistance]] of the device is at its minimum. When the magnetic field causes the free layer magnetization vector to rotate in a direction antiparallel to the pinned layer magnetization vector, the electrical resistance of the device increases due to spin-dependent scattering. The magnitude of the change, (Antiparallel Resistance - Parallel Resistance) / Parallel Resistance x 100% is called the GMR ratio. Devices have been demonstrated with GMR ratios as high as 200% with typical values greater than 10%. This is a vast improvement (hence the term "giant") over the [[Anisotropy|anisotropic]] magnetoresistance effect in single layer materials which is usually less than 3%. Spin valves can be designed with magnetically soft free layers which have a sensitive response to very weak fields (such as those originating from tiny magnetic bits on a computer disk), and have replaced anisotropic magnetoresistance sensors in computer disk drive [[disk read-and-write head|heads]] since the late 1990s. Future applications may include a spin-based [[transistor]] which requires the development of [[magnetic semiconductors]] exhibiting room temperature [[ferromagnetism]]. One possible material candidate is manganese doped gallium arsenide [[GaAs:Mn]]. The operation of [[MRAM]] or magnetic random access memory is also based on spintronic principles. Spintronics-based non-volatile [[3D optical data storage]] has also been proposed. Multiferroics which change internal molecular geometry under electrostatic or electromagnetic influence are a hotbed of research at several universities. == See also == * [http://www.spintronicskc.com Spintronics] * [[Spin pumping]] * [[Spin transfer]] * [[Spinhenge@Home]] ==References== <references/> == Further reading == * ''Ultrafast Manipulation of Electron Spin Coherence''. J. A. Gupta, R. Knobel, N. Samarth and D. D. Awschalom in Science, Vol. 292, pages 2458-2461; June 29, 2001. * ''Spintronics: A Spin-Based Electronics Vision for the Future''. S. A. Wolf et al, Science '''294''', 1488-1495 (2001) * ''How to Create a Spin Current''. P. Sharma, Science '''307''', 531-533 (2005) * Search Google Scholar for highly cited articles with query: spintronics OR magnetoelectronics OR "spin based electronics" * "Electron Manipulation and Spin Current". D. Grinevich. 3rd Edition, 2003.* ==External links== * {{cite journal |url=http://www.sciam.com/article.cfm?articleID=0007A735-759A-1CDD-B4A8809EC588EEDF |title=Spintronics |journal=Scientific American |date=June 2002 |unused_data=accessdate-}} * [http://www.informationweek.com/news/internet/showArticle.jhtml?articleID=207200184 RaceTrack:InformationWeek (April 11, 2008)] * [http://domino.research.ibm.com/comm/pr.nsf/pages/news.20030610_mram.html IBM (2003)] * [http://www.wired.com/news/technology/0,1282,59559,00.html Wired: update on MRAMs, 2003 Jul] * [http://www.eetimes.com/news/semi/showArticle.jhtml?articleID=191504070 Spintronics research targets [[GaAs]].] * [http://www.albany.edu/spin/ Spintronics at SUNY Albany's College of Nanoscale Science and Engineering] * [http://www.spintronics-info.com/ Spintronics information community site] * [http://in.news.yahoo.com/indiaabroad/20080412/r_t_ians_tc_software/ttc-ibm-to-use-spintronics-to-increase-c-0a92fdb.html IBM to use 'spintronics' to increase computer memory capacity (April 12, 2008)] [[Category:Spintronics| ]] [[Category:Classes of computers]] [[Category:Theoretical computer science]] [[de:Spintronik]] [[es:Espintrónica]] [[fr:Spintronique]] [[ko:스핀트로닉스]] [[it:Spintronica]] [[ja:スピントロニクス]] [[pl:Spintronika]] [[pt:Spintrônica]] [[ru:Спинтроника]] [[sv:Spinntronik]] [[vi:Điện tử học spin]] [[tr:Spintronik]] [[zh-yue:自旋電子學]] [[zh:自旋電子學]] [[uk:Спінтроніка]]