Download magnetism

Physical Attraction
The Mysteries of Magnetism
Joachim Stöhr
SSRL/SLAC
Magnetism and Humans
Magnetic Attraction
“Animal Magnetism” –
Mesmerizing –
Magnetic Healing
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……ultra-small, ultra-fast
A historical perspective
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
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.
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 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 field mostly from electric currents in the liquid iron outer core
Field changes direction about every 500,000 years
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)
“The mystery of magnetism, explain that to me !
Around 1800: No greater mystery, except love and hate.”
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!
1819 – a breakthrough discovery
Hans Christian Oersted
(Denmark, 1777-1851)
1831: The foundation of the industrial society
Michael Faraday
(England, 1791 – 1867)
Electric generator:
motion
electricity
Electric motor:
electricity
motion
Electricity is big $$$$$$$
US electricity retail sales:
$ 250 billion/year ($ 0.25 trillion)
Total Gross Domestic Product (trillions of $)
1. United States
2. Japan
3. Germany
4. United Kingdom
5. France
6. Italy
7. China
10.9
Hydro-electric - water drives turbine
4.3
2.4 Nuclear - heats water - steam - turbine
1.8
1.7
1.5 Fuel - burns - hot gases - turbine
1.4
About half of the US energy is consumed as electricity
1845: Magnetism and light – a connection !
again…
Michael Faraday
1791 - 1867
Light must have a magnetic component
1864: Maxwell’s equations: coupling of electric and magnetic phenomena
Light is an electromagnetic wave
James Clerk Maxwell
Ludwig Boltzmann (Germany,1844-1906)
(Scotland, 1831 – 1879)
“Was it a god who wrote these symbols
…unveiling the forces of nature?”
only wavelength is different
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 inside of magnets: origin of magnetism
magnet = arrangement of atoms with aligned spins
Magnetism today……
the high-tech society…
……beyond electricity and wireless
The spin on electronics:
magnetic devices in computers
“chip - RAM”
“disk”
“0” and “1” bits = small magnetic areas with opposite magnetization direction
Magnetic recording technology
Courtesy of Jan Thiele, Hitachi
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
Magnetic recording: Small and fast !
1 mile/hour
1000 miles/hour
The invisible ultra-small world
understand size limits
-- no stable bits--
X-ray images … then and now
X-rays have come a long way……
1
0 “bits”
10,000 times
smaller
1895
W. Röntgen, Würzburg
1993
SSRL/SLAC
A Glimpse of the Future……
exploring ultrafast time scales
….is there a data storage speed limit ?
Present switching pulses are generated by current flow through wires
“Oersted fields”
most advanced technology:
100 picosecond (10 billionth of a second) current pulses
magnetic recording works fine
With this method we cannot explore faster switching today
…. is there a speed limit ????
The ultra-fast world
How can we explore
this void?
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
Artificial “lightning bolt” – an electron accelerator
Magnetic writing with SLAC beam
sample
The Speed Limit of Magnetic Switching
tpulse= 3 ps
1
0
1
0
tpulse= 100 fs
1
90 mm
90 mm
30 times faster than conventional
-- switching still works reliably --
There is a speed limit!
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
The future: seeing the invisible at ultrafast speeds
Linac Coherent Light Source – LCLS
the first x-ray laser in the world
to come in 2008
Near Hall
FEL Center
Far Hall
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
•
remains an exciting research topic
may be used in future for computer memory and “quantum computing”
... 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