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Magnetic Memory: Data Storage and Nanomagnets

Magnetic Memory: Data Storage and Nanomagnets. Mark Tuominen UMass. Kathy Aidala Mount Holyoke College. Data. Data is information. iTunes. How do we store data digitally?. Everything is reduced to binary, a “ 1 ” or a “ 0 ” .

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Magnetic Memory: Data Storage and Nanomagnets

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  1. Magnetic Memory: Data Storage and Nanomagnets Mark Tuominen UMass Kathy Aidala Mount Holyoke College

  2. Data Data is information iTunes

  3. How do we store data digitally? Everything is reduced to binary, a “1” or a “0”. We look for ways to represent 1 or 0, which means we need to find physical systems with two distinct states. We have to be able to switch the state of the system if we want to “write” data. The bit has to stay that way for long enough. We have to be able to “read” if the bit is a zero or one to use the data. What physical systems have these properties??

  4. 20 GB 40 GB 10 GB 2001 2002 2004 Hard drive Magnetic data storage 80 GB 160 GB 2006 2007 Review Data Storage. Example: Advancement of the iPod Uses nanotechnology!

  5. www.ndt-ed.org/EducationResources MAGNETISM I B Electrical current produces a magnetic field: "electromagnetism"

  6. www.eia.doe.gov www.how-things-work-science-projects.com MAGNETISM myfridge Refrigerator magnets provide an external magnetic field, permanently; no wires, no power supply and no current needed. Permanent Magnets = FERROMAGNETS

  7. anisotropy axis ("easy" axis) Ferromagnet uniform magnetization • Electron magnetic moments ("spins") • Aligned by • "exchange interaction" Bistable ! Equivalent energy for "up" or "down” states Iron, nickel, cobalt and many alloys are ferromagnets

  8. Mz H The Bistable Magnetization of a Nanomagnet • A single-domain nanomagnet with a single “easy axis” (uniaxial anisotropy) has two stable magnetization states Mz Mz z or H hysteresis curve “topview” shorthand switching field E = K1sin2•H Bistable! Ideal for storing data - in principle, even one nanomagnet per bit.

  9. Current S ‘0’ N Current N ‘1’ S “Writing” data to a ferromagnet ? Ferromagnet with unknown magnetic state

  10. “Read” Head Signal 0 0 1 0 1 0 0 1 1 0 _ _ “Bits” of information Magnetic Data Storage A computer hard drive stores your data magnetically “Write” Head current S N Disk N S direction of disk motion

  11. 25 DVDs on a disk the size of a quarter. Scaling Down to the Nanoscale Increases the amount of data stored on a fixed amount of “real estate” ! Now ~ 100 billion bits/in2, future target more than 1 trillion bits/in2

  12. Nanofabrication with self-assembled “cylindrical phase” diblock copolymer films Deposition Template Remove polymer block within cylinders (expose and develop) UMass/IBM: Science 290, 2126 (2000)

  13. electrolyte CE WE REF Co2+ Co Filling the Template: Making Cobalt Nanorods by Electrochemical Deposition metal

  14. 4 choices two bits 00, 01, 10, 11 000, 001, 010, 011, 100, 101, 110, 111 three bits 8 choices Binary Representation of Data only 2 choices one bit “1” or “0” or n bits has 2n choices For example, 5 bits has 25 = 32 choices… more than enough to represent all the letters of the alphabet

  15. Binary representation of lower case letters N N OR N N S S N 1 0 0 1 1 S S S 5-bit "Super Scientist" code: For example, k = 01011 (Coding Activity: Use attractive and repulsive forces to "read" the magnetic data!)

  16. Vortex Magnetization "0" "1" Ferromagnetic Nanorings as Memory Pt solid tip Nanotechnology(2008); PRB (2009)

  17. AFM: Electromagnetic Forces • Anything that creates a force on the tip can be “imaged” • Electromagnetic force is long range, but generally weaker than the repulsive forces at the surface • Image electromagnetic forces 10 – 100nm above the surface Lift height

  18. Magnetic Force Microscopy Computer Hard Drive magnetic tip

  19. Magnetic Force Microscopy Computer Hard Drive magnetic tip Topography

  20. Magnetic Force Microscopy Computer Hard Drive magnetic tip Topography Lift height

  21. Magnetic Force Microscopy Computer Hard Drive magnetic tip Topography Lift height Magnetism

  22. Magnetic Force Microscopy Image contrast is proportional to the derivative of the magnetic field Magnetic state dB/dz small dB/dz large, negative dB/dz large, positive MFM simulation 200 nm

  23. MFM of Ring States Symmetric Rings

  24. MFM of Ring States Symmetric Rings vortex onion • No contrast in the vortex state in a perfect ring. Cannot determine circulation (CW or CCW) • Light and Dark spots indicate Tail to Tail and Head to Head domain walls. onion

  25. Switching: Onion to Vortex 1 2 3 4 1 um T. Yang, APL, 98, 242505 (2011).

  26. Switching: Onion to Vortex 1 2 3 4 Stronger field (40 mA = 178 Oe) 1 um Weaker field (30 mA = 133 Oe) T. Yang, APL, 98, 242505 (2011).

  27. Switching: Onion to Vortex 1 2 3 4 Stronger field (40 mA = 178 Oe) 1 um Weaker field (30 mA = 133 Oe) T. Yang, APL, 98, 242505 (2011).

  28. Improved MRAM Proposal Trapped DWs lead to lower switching current Zhu, Proceedings of the IEEE 96(11), 1786 (2008)

  29. Proof of Principle Cobalt, 12nm thick Nanotechnology, 22 (2011) 485705

  30. Vortex Magnetization "0" "1" Ferromagnetic Nanorings as Memory Pt solid tip Nanotechnology(2008); PRB (2009) Aidala and Tuominen, APL (2011); Nanotech. 2011; J.A.P. 2012 Manipulation of magnetization with local circular field

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