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The Magic of Magnetism From Physical Attraction to Spin Doctors

Explore the fascinating world of magnetism, from its historical origins to its applications in today's high-tech society. Learn about the magnetic properties of objects, the development of magnetic devices, and the future of magnetism in spintronics. Discover how magnetism has shaped our understanding of the world and continues to play a vital role in various fields.

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The Magic of Magnetism From Physical Attraction to Spin Doctors

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  1. The Magic of Magnetism From Physical Attraction to Spin Doctors Joachim Stöhr Stanford Synchrotron Radiation Laboratory Stanford Linear Accelerator Center

  2. Magnetism and Humans “Animal Magnetism” –Mesmerizing – Magnetic Healing Magnetic Personality - Attraction - From myth to science …..

  3. Magnetic Objects

  4. Magnetic Devices

  5. Overview of Talk • A historical perspective … the spin on magnetism … • Magnetism today… the hi-tech society • A Glimpse of the Future…… spin electronics, “spintronics”

  6. A historical perspective

  7. The term “magnetism” Legend: Shepherd by the name of Magnés found that his iron tipped cane was attracted to rocks More probable: Name comes from city of Magnesia (modern Turkey) surrounded by magnetic rock deposits Thales of Miletus (Greek, ~634 - 546 BC) first described “magnetism” as the attraction of iron by ``lodestone“ - lodestone is the naturally occurring mineral magnetite Fe3O4

  8. Si Nan - the south governor China, ca. 200 BC magnetic lodestone spoon south bronze plate direction pointers likely used for feng shui - the method of achieving harmony with the forces of nature by properly aligning buildings and placing of objects.

  9. Earth is magnetic - compass follows its field Naval navigation: China in late 11th or early 12th century compass became known in Europe sometime later in the 12th century In 1600William Gilbert published his book “De Magnete“ - “About the Magnet“ he explained that compass needle points north-south because earth is magnetic William Gilbert (England, 1544-1603)

  10. Earth field mostly from electric currents in the liquid iron outer core Field changes direction about every 500,000 years

  11. Around 1800: mythical magnetism Franz Anton Mesmer theorized that "animal magnetism" accounted for his ability to heal. Mesmerizing a patient Franz Anton Mesmer (Germany/Austria 1734-1815)

  12. “The mystery of magnetism, explain that to me! No greater mystery but love and hate.” Around 1800: magnetism is fundamental, it is just there – it does not need to be explained Natural Philosophy: two opposites make a “whole” love – hate black – white north – south plus – minus Johann Wolfgang von Goethe (Germany, 1749-1832) …contains important modern element: there are no magnetic monopoles!

  13. 1819 – a breakthrough discovery Hans Christian Oersted (Denmark, 1777-1851)

  14. The right hand rule:

  15. 1831: The foundation of the industrial society Electric generator: motion electricity Electric motor: electricity motion Michael Faraday (England, 1791 – 1867)

  16. Electricity is big $$$$$$$ US electricity retail sales: $ 250 billion/year ($ 0.25 trillion) Total Gross Domestic Product (trillions of $) 1. United States 10.9 (electricity is 2.5 %) 2. Japan 4.3 3. Germany 2.4 4. United Kingdom 1.8 5. France 1.7 6. Italy 1.5 7. China 1.4 Hydro-electric - water drives turbine Nuclear - heats water - steam - turbine Fuel - burns - hot gases - turbine

  17. 1845: Magnetism and light – a connection ! again… Michael Faraday 1791 - 1867 Light must have a magnetic component

  18. 1864: Maxwell’s equations: coupling of electric and magnetic phenomena Light is an electromagnetic wave James Clerk Maxwell Ludwig Boltzmann(Germany,1844-1906) “Was it a god who wrote these symbols …unveiling the forces of nature?” (Scotland, 1831 – 1879)

  19. only wavelength is different

  20. The electro-magnetic spectrum: “wireless waves at the speed of light” Visible light It is hard to imagine our society without wireless technology !

  21. From classical magnetism & electro-magnetism to spin doctors

  22. 1921-1928: Getting to the origin of magnetism 7 years that changed physics and magnetism • The concept of thespin (Pauli, Uhlenbeck & Goudsmit, Dirac) • Quantum theory (Heisenberg, Schrödinger, Dirac) • Magnetic exchange interaction in materials (Heisenberg) The mystery of spin: when measured, it is always along a “quantization axis” – “up” or “down”

  23. The inside of magnets: origin of magnetism magnet = arrangement of atoms with aligned spins

  24. Aligning or “switching” a magnetic material - Oersted’s method still used after 186 years !- Magnetic material, e.g iron current magnetic regions “domains”

  25. Magnetism and Magnetic Materials today…… the high-tech society…

  26. The spin on electronics: magnetic devices in computers “chip - RAM” “disk” “0” and “1” bits = small magnetic areas with opposite magnetization direction

  27. Magnetic recording technology Courtesy of Jan Thiele, Hitachi

  28. The Data Storage Industry $53 billion/year worldwide revenues IBM RAMAC 1956: 1 song stack of 50 giant discs, 24" diameter total 4.4 MB - $35,000/year rent Today: 200 GB = 200, 000 MB - $ 90 10,000 songs

  29. Brightness of x-ray sources “smaller and faster”

  30. X-rays have come a long way…… x-ray images … then and now 1 0 “bits” 10,000 times smaller 1895 W. Röntgen, Würzburg 1993 Magnetic x-ray image

  31. ALS The Power of X-Rays

  32. A Glimpse of the Future…… exploring spin-electronics “spintronics”

  33. Beyond Oersted’s method – “spin doctoring” The concept of a “spin polarized current” copper copper electrons magnetic atoms in iron spin polarized current spins

  34. Spin currents: a new way of magnetic switching: electric current creates magnetic field “Oersted field” spin current acts like an “Exchange field” sensor layer current current referencelayer sensor layer Weak, long range Strong, short range

  35. Switching of magnetic memory cells (MRAM) cell to be switched switching by Oersted field around wire better: switching by current in wire current current

  36. X-ray microscopy image of spin injection structure 100 x 300 nm x-ray image y x leads for ns current pulses Detector

  37. Movie 1

  38. X-Ray microscopy images of magnetization in buried sensor layer After current in one direction After current in other direction magnetization has complicated “horseshoe” state

  39. Movie 2

  40. Next time… not cartoons but … real x-ray movies !

  41. In Summary….. • Magnetism …. • is an old phenomenon and topic • has many important practical applications • navigation … electricity … wireless communication… medical imaging • underlies modern data storage technology • “spin doctoring” may be used for switching of • computer memory and “quantum computing” • remains an exciting research topic ... the mystery of magnetism continues...

  42. Acknowledgements Yves Acremann, SSRL Ann Mueller, SSRL Michael Hyde, SLAC Science website: http://www.howstuffworks.com My research group: http://www-ssrl.slac.stanford.edu/stohr http://www-ssrl.slac.stanford.edu/stohrgroup New book: J. Stöhr and H. C. Siegmann Magnetism: From Fundamentals to Nanoscale Dynamics Springer Verlag, February/March 2006

  43. The end

  44. Magnetic recording: Small and fast ! 1 mile/hour 1000 miles/hour Incredibly small bits – incredible writing and reading speeds

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