the magic of magnetism from physical attraction to spin doctors joachim stöhr stanford synchrotron...

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  • The Magic of Magnetism From Physical Attraction to Spin Doctors Joachim Sthr

    Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center

  • Magnetism and Humans Magnetic Personality- Attraction - Animal Magnetism Mesmerizing Magnetic HealingFrom myth to science ..

  • Magnetic Objects

  • Magnetic Devices

  • Overview of Talk A historical perspective the spin on magnetism

    Magnetism today the hi-tech society

    A Glimpse of the Future spin electronics, spintronics

  • A historical perspective

  • first described magnetism as the attraction of iron by ``lodestone- lodestone is the naturally occurring mineral magnetite Fe3O4

    Thales of Miletus (Greek, ~ 634 - 546 BC) Legend: Shepherd by the name of Magns found that his iron tipped cane was attracted to rocks The term magnetismMore probable:Name comes from city of Magnesia (modern Turkey) surrounded by magnetic rock deposits

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

    magnetic lodestone spoon

  • In 1600 William Gilbert published his bookDe Magnete - About the Magnet

    he explained that compass needle points north-south because earth is magnetic

    William Gilbert (England, 1544-1603) Earth is magnetic - compass follows its fieldNaval navigation:China in late 11th or early 12th century compass became known in Europe sometime later in the 12th century

  • Earth field mostly from electric currents in the liquid iron outer core

    Field changes direction about every 500,000 years

  • Franz Anton Mesmer theorized that "animal magnetism" accounted forhis ability to heal. (Germany/Austria 1734-1815) Around 1800: mythical magnetismFranz Anton MesmerMesmerizing a patient

  • The mystery of magnetism, explain that to me ! No greater mystery but love and hate.Natural Philosophy:

    two opposites make a wholelove hateblack white north southplus minus magnetism is fundamental, it is just there it does not need to be explained Johann Wolfgang von Goethe (Germany, 1749-1832)Around 1800:contains important modern element: there are no magnetic monopoles!

  • (Denmark, 1777-1851) Hans Christian Oersted 1819 a breakthrough discovery

  • The right hand rule:

  • 1831: The foundation of the industrial societyElectric generator: motion electricity (England, 1791 1867)Michael FaradayElectric motor: electricity motion

  • Fuel - burns - hot gases - turbine US electricity retail sales: $ 250 billion/year ($ 0.25 trillion)Electricity is big $$$$$$$Nuclear - heats water - steam - turbine Hydro-electric - water drives turbine

    Total Gross Domestic Product (trillions of $)

    1. United States 10.9 (electricity is 2.5 %) 2. Japan 4.33. Germany 2.44. United Kingdom 1.85. France 1.7 6. Italy 1.57. China 1.4

  • 1845: Magnetism and light a connection !1791 - 1867again

    Michael Faraday Light must have a magnetic component

  • (Scotland, 1831 1879)1864: Maxwells equations: coupling of electric and magnetic phenomenaLight is an electromagnetic wave Ludwig Boltzmann (Germany,1844-1906)

    Was it a god who wrote these symbolsunveiling the forces of nature? James Clerk Maxwell

  • only wavelength is different

  • The electro-magnetic spectrum: wireless waves at the speed of lightVisible lightIt is hard to imagine our society without wireless technology !

  • From

    classical magnetism & electro-magnetism


    spin doctors

  • 1921-1928: Getting to the origin of magnetism 7 years that changed physics and magnetism The concept of the spin (Pauli, Uhlenbeck & Goudsmit, Dirac)

    Quantum theory (Heisenberg, Schrdinger, Dirac)

    Magnetic exchange interaction in materials (Heisenberg)The mystery of spin: when measured, it is always along a quantization axis up or down

  • The inside of magnets: origin of magnetismmagnet = arrangement of atoms with aligned spins

  • currentAligning or switching a magnetic material - Oersteds method still used after 186 years ! -magnetic regions domainsMagnetic material, e.g iron

  • Magnetism and Magnetic Materials today

    the high-tech society

  • The spin on electronics: magnetic devices in computers0 and 1 bits = small magnetic areas with opposite magnetization directionchip - RAMdisk

  • Magnetic recording technologyCourtesy of Jan Thiele, Hitachi

  • stack of 50 giant discs, 24" diametertotal 4.4 MB - $35,000/year rent Today:200 GB = 200, 000 MB - $ 90IBM RAMAC 1956: The Data Storage Industry $53 billion/year worldwide revenues10,000 songs1 song

  • smaller and fasterBrightness of x-ray sources

  • x-ray images then and now 1895W. Rntgen, Wrzburg 1993 Magnetic x-ray imageX-rays have come a long way10,000 times smaller01bits

  • The Power of X-Rays ALS

  • A Glimpse of the Future

    exploring spin-electronics


  • Beyond Oersteds method spin doctoring The concept of a spin polarized current electronsmagnetic atoms in ironcoppercopperspinsspin polarized current

  • Weak, long range spin current acts like anExchange fieldelectric current creates magnetic field Oersted fieldStrong, short rangeSpin currents: a new way of magnetic switching:reference layersensorlayercurrentsensorlayercurrent

  • Switching of magnetic memory cells (MRAM)currentcurrent cell to be switchedbetter: switching by current in wireswitching by Oersted field around wire

  • X-ray microscopy image of spin injection structure100 x 300 nmDetectorxy leads for nscurrent pulsesx-ray image

  • Movie 1

  • magnetization has complicated horseshoe stateX-Ray microscopy images of magnetization in buried sensor layerAfter current in one directionAfter current in other direction

  • Movie 2

  • Next time

    not cartoons but

    real x-ray movies !

  • 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...

  • AcknowledgementsYves Acremann, SSRLAnn Mueller, SSRLMichael Hyde, SLAC

    Science website:

    My research group: New book: J. Sthr and H. C. Siegmann Magnetism: From Fundamentals to Nanoscale Dynamics Springer Verlag, February/March 2006

  • The end

  • Magnetic recording: Small and fast !1 mile/hour1000 miles/hourIncredibly small bits incredible writing and reading speeds

    Two types of switching. Will mention spin polarized electrons, but I will not explain in detail see slide 4Consider redrawing picture to improve resolution


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