Spin-transfer torque - Wikipedia, the free encyclopedia http://en.wikipedia.org/wiki/Spin-transfer_torque Spin-transfer torque From Wikipedia, the free encyclopedia Spin-transfer torque is an effect in which the orientation of a magnetic layer in a magnetic tunnel junction or spin valve can be modified using a spin-polarized current. Charge carriers (such as electrons) have a property known as spin which is a small quantity of angular momentum intrinsic to the carrier. An electrical current is generally unpolarized (consisting of 50% spin-up and 50% spin-down electrons); a spin polarized current is one with more electrons of either spin. By passing a current through a thick magnetic layer, one can produce a spin-polarized current. If a spin-polarized current is directed into a magnetic layer, angular momentum can be transferred to the layer, changing its orientation. This can be used to excite oscillations or even flip the orientation of the magnet. The effects are usually only seen in nanometer scale devices. A simple model of spin-transfer torque for two anti-aligned layers. Current flowing out of the free layer is spin-polarized. When it reaches the free layer the majority spins relax into lower-energy states of opposite spin, applying a torque to the free layer in the process. Contents 1 Spin-transfer torque memory 2 See also 3 References 4 External links Spin-transfer torque memory Spin-transfer torque can be used to flip the active elements in magnetic random-access memory. Spin-transfer torque randomaccess memory, or STT-RAM, has the advantages of lower power consumption and better scalability over conventional magnetoresistive random-access memory (MRAM) which uses magnetic fields to flip the active elements. The name STT-RAM was first coined by Grandis, Inc.[citation needed] Spin-transfer torque technology has the potential to make possible MRAM devices combining low current requirements and reduced cost; however, the amount of current needed to reorient the magnetization is at present too high for most commercial applications, and the reduction of this current density alone is the basis for current academic research in spin electronics.[1] Hynix Semiconductor and Grandis formed a partnership in April 2008 to explore commercial development of STT-RAM technology.[2][3] On August 1, 2011, Grandis announced that it had been purchased by Samsung Electronics for an undisclosed sum.[4] Hitachi and Tohoku University demonstrated a 32-Mbit STT-RAM in June 2009.[5] Other companies working on STT-RAM include Crocus Technology[6] and Spin Transfer Technologies.[7] In May 2011, Russian Nanotechnology Corp. announced an investment of $300 millions in Crocus Technology which will build an MRAM factory in Russia. A schematic diagram of a spin valve/magnetic tunnel junction. In a spin valve the spacer layer (purple) is metallic; in a magnetic tunnel junction it is insulating. See also Magnetoresistive random-access memory Spin (physics) Memresistor Spintronics References 1. ^ Ralph, D.C.; M.D. Stiles (2008-04). "Spin transfer torques" (http://www.sciencedirect.com/science/article/B6TJJ-4RFSD1M-2/2/f35a2bc5e9c53f19f6883d74c20dbb69) . Journal of Magnetism and Magnetic Materials 320 (7): 1190–1216. doi:10.1016/j.jmmm.2007.12.019 (http://dx.doi.org/10.1016%2Fj.jmmm.2007.12.019) . ISSN 0304-8853 (http://www.worldcat.org /issn/0304-8853) . http://www.sciencedirect.com/science/article/B6TJJ-4RFSD1M-2/2/f35a2bc5e9c53f19f6883d74c20dbb69. Retrieved 2009-05-22. 2. ^ "Grandis press release describing partnership with Hynix" (http://www.grandisinc.com/pdf/Grandis_PR_Apr01_2008.pdf) . Grandis. 2008-04-01. http://www.grandisinc.com /pdf/Grandis_PR_Apr01_2008.pdf. Retrieved 2008-08-15. 3. ^ "Hynix press release describing partnership with Grandis" (http://www.hynix.com/gl/pr_room/news_data_readA.jsp?NEWS_DATE=2008-04-02:09:14:16&CurrentPageNo=1& SearchKind=4&SearchWord=&SELECT_DATE=&menuNo=02&m=01&s=01) . Hynix. 2008-04-02. http://www.hynix.com/gl/pr_room /news_data_readA.jsp?NEWS_DATE=2008-04-02:09:14:16&CurrentPageNo=1&SearchKind=4&SearchWord=&SELECT_DATE=&menuNo=02&m=01&s=01. Retrieved 2008-08-15. 4. ^ http://www.foxbusiness.com/technology/2011/08/01/samsung-buys-grandis-as-mram-moves-toward-mainstream/#ixzz1TpEGFRmD 5. ^ http://www.vlsisymposium.org/2009/circuits/cir_abstract/8-4.htm 6. ^ "Crocus press release describing MRAM new prototype" (http://www.crocus-technology.com/pr-10-01-09.html) .Crocus. 2009-10-01. 7. ^ http://www.mram-info.com/interview-vicent-chun-spin-transfer-technologies External links Spin torque applet (http://www.bama.ua.edu/~tmewes/Java/dynamics/MagnetizationDynamics2.shtml) Solicitation Number: BAA08-16 from the Defense Advanced Research Projects Agency (https://www.fbo.gov/download/626/6263f8ac72a2b77bda4d21677b5102cb /stt_ram_baa_08_16_v4__cmo_26feb08.pdf) J.C. Slonczewski:"Current-driven excitation of magnetic multilayers(1996)", Journal of Magnetism and Magnetic Materials Volume 159, Issues 1-2, June 1996, Pages L1-L7 [1] (http://dx.doi.org/10.1016/0304-8853(96)00062-5) Crocus technology (http://www.crocus-technology.com/) Retrieved from "http://en.wikipedia.org/w/index.php?title=Spin-transfer_torque&oldid=476306797" Categories: Computer hardware stubs Spintronics This page was last modified on 11 February 2012 at 17:41. Text is available under the Creative Commons Attribution-ShareAlike License; additional terms may apply. See Terms of use for details. Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization. 1 of 1 2/21/2012 5:03 PM