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Magnetism and Humans
Magnetic 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……ultra-small, ultra-fast
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, except 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
About half of the US energy is consumed as electricity
Total Gross Domestic Product (trillions of $)
1. United States 10.92. 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”
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
Magnetic recording: Small and fast !
1 mile/hour
1000 miles/hour
Incredibly small bits – incredible writing and reading speeds
X-ray images … then and now
1895W. Röntgen, Würzburg
1993SSRL/SLAC
X-rays have come a long way……
10,000 times smaller
01 “bits”
With this method we cannot explore faster switching today …. is there a speed limit ????
Present switching pulses are generated by current flow through wires
most advanced technology: 100 picosecond (10 billionth of a second) current pulsesmagnetic recording works fine
“Oersted fields”
An electro-magnetic brainstorm
Create an artificial “lightning bolt”and use it to switch a magnetic sample !
(Prof. ETH Zürich, Switzerland)
Creation of large, ultrafast magnetic fields
Conventional method
- t
oo slow
Artificial “lightning bolt” – an electron accelerator
The Speed Limit of Magnetic Switching
tpulse= 3 ps tpulse= 100 fs
30 times faster than conventional -- switching still works reliably --
There is a speed limit!
90 m90 m
01 01 1
1000 times faster than conventional -- switching is not reliable --
.. but we don’t understand why!
The magnetic recording limits: size and speed
size speed
factor < 1000 to go
factor 30 x 150 ~ 5000 to go
Linac Coherent Light Source – LCLS the first x-ray laser in the world
Near Hall
Far Hall
FEL Center
to come in 2008
The future: seeing the invisible at ultrafast speeds
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 may be used in future for computer memory and “quantum computing”
• remains an exciting research topic
... the mystery of magnetism continues...
Acknowledgements
Ann Mueller, SSRL
Science website:http://www.howstuffworks.com
My research group:http://www-ssrl.slac.stanford.edu/stohr
http://www-ssrl.slac.stanford.edu/stohrgroup