the magic of magnetism from physical attraction to spin doctors joachim stöhr stanford synchrotron...
TRANSCRIPT
The Magic of Magnetism From Physical Attraction to Spin Doctors
Joachim Stöhr
Stanford Synchrotron Radiation LaboratoryStanford Linear Accelerator Center
Magnetism and Humans
Magnetic Personality
- Attraction -
“Animal Magnetism” –Mesmerizing –
Magnetic Healing
From myth
to sc
ience …
..
Overview of Talk
• A historical perspective … the spin on magnetism …
• Magnetism today… the hi-tech society
• A Glimpse of the Future…… spin electronics, “spintronics”
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 Magnés found that his iron tipped cane was attracted to rocks
The term “magnetism”
More probable:Name comes from city of Magnesia (modern Turkey) surrounded by magnetic rock deposits
Si Nan - the south governor China, ca. 200 BC
bronze plate
south
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.
magnetic lodestone spoon
In 1600 William 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)
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
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 magnetism
Franz Anton Mesmer
Mesmerizing a patient
“The mystery of magnetism, explain that to me ! No greater mystery but love and hate.”
Natural Philosophy:
two opposites make a “whole”love – 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!
1831: The foundation of the industrial society
Electric generator: motion electricity
(England, 1791 – 1867)
Michael Faraday
Electric 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 - 1867
again…
Michael Faraday
Light must have a magnetic component
(Scotland, 1831 – 1879)
1864: Maxwell’s equations: coupling of electric and magnetic phenomena
Light is an electromagnetic wave
Ludwig Boltzmann (Germany,1844-1906)
“Was it a god who wrote these symbols…unveiling the forces of nature?”
James Clerk Maxwell
The electro-magnetic spectrum: “wireless waves at the speed of light”
Visible light
It is hard to imagine our society without wireless technology !
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, Schrödinger, Dirac)
• Magnetic exchange interaction in materials (Heisenberg)
The mystery of spin: when measured, it is always along a “quantization axis” – “up” or “down”
current
Aligning or “switching” a magnetic material - Oersted’s method still used after 186 years ! -
magnetic regions “domains”
Magnetic material, e.g iron
The spin on electronics: magnetic devices in computers
“0” and “1” bits = small magnetic areas with opposite magnetization direction
“chip - RAM”
“disk”
stack of 50 giant discs, 24" diameter
total 4.4 MB - $35,000/year rent
Today:
200 GB = 200, 000 MB - $ 90
IBM RAMAC 1956:
The Data Storage Industry $53 billion/year worldwide revenues
10,000 songs
1 song
x-ray images … then and now
1895W. Röntgen, Würzburg
1993 Magnetic x-ray image
X-rays have come a long way……
10,000 times smaller
01 “bits”
Beyond Oersted’s method – “spin doctoring”
The concept of a “spin polarized current”
electrons magnetic atoms in iron
copper copper
spinsspin polarized current
Weak, long range
spin current acts like an
“Exchange field”
electric current creates magnetic field
“Oersted field”
Strong, short range
Spin currents: a new way of magnetic switching:
referencelayer sensor
layer
current
sensorlayer
current
Switching of magnetic memory cells (MRAM)
current current
cell to be switched
better: switching by current in wireswitching by Oersted field around wire
X-ray microscopy image of spin injection structure
100 x 300 nm
Detector
xy
leads for nscurrent pulses
x-ray image
magnetization has complicated “horseshoe” state
X-Ray microscopy images of magnetization in buried sensor layer
After current in one direction After current in other direction
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: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