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 ..
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 !
classical magnetism & electro-magnetism
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
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
magnetization has complicated horseshoe stateX-Ray microscopy images of magnetization in buried sensor layerAfter current in one directionAfter current in other direction
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
My research group:http://www-ssrl.slac.stanford.edu/stohr
http://www-ssrl.slac.stanford.edu/stohrgroup New book: J. Sthr and H. C. Siegmann Magnetism: From Fundamentals to Nanoscale Dynamics Springer Verlag, February/March 2006
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