A1257787414NcyTA

1
The Magic of Magnetism From
Physical Attraction to Spin Doctors
Joachim Stöhr Stanford Synchrotron Radiation
Laboratory Stanford Linear Accelerator Center
2
Magnetism and Humans
Animal Magnetism Mesmerizing Magnetic
Healing
Magnetic Personality - Attraction -
From myth to science ..
3
Magnetic Objects
4
Magnetic Devices
5
Overview of Talk

• A historical perspective the spin on magnetism
  
• Magnetism today the hi-tech society
• A Glimpse of the Future spin electronics,
  spintronics

6
A historical perspective

7
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
8
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.
9
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)
10
Earth field mostly from electric currents in the
liquid iron outer core
Field changes direction about every 500,000 years
11
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)
12
The mystery of magnetism, explain that to me !
No greater mystery but love and hate.
Around 1800
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!
13
1819 a breakthrough discovery
Hans Christian Oersted
(Denmark, 1777-1851)
14
(No Transcript)
15
The right hand rule
16
1831 The foundation of the industrial society
Electric generator motion
electricity
Electric motor electricity
motion
Michael Faraday
(England, 1791 1867)
17
Electricity is big
US electricity retail sales 250
billion/year ( 0.25 trillion)
Total Gross Domestic Product (trillions of ) 1.
United States 10.9 (electricity is 2.5
) 2. Japan 4.3 3.
Germany 2.4 4. United Kingdom
1.8 5. France 1.7 6.
Italy 1.5 7. China
1.4
Hydro-electric - water drives turbine
Nuclear - heats water - steam - turbine
Fuel - burns - hot gases - turbine
18
1845 Magnetism and light a connection !
again Michael Faraday
1791 - 1867
Light must have a magnetic component
19
1864 Maxwells equations coupling of electric
and magnetic phenomena
Light is an electromagnetic wave
James Clerk Maxwell
Ludwig Boltzmann (Germany,1844-1906) Was it a
god who wrote these symbols unveiling the forces
of nature?
(Scotland, 1831 1879)
20
only wavelength is different
21
The electro-magnetic spectrum wireless waves
at the speed of light
Visible light
It is hard to imagine our society without
wireless technology !
22
From classical magnetism
electro-magnetism to spin doctors
23
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
24
The inside of magnets origin of magnetism
magnet arrangement of atoms with aligned spins
25
Aligning or switching a magnetic material
- Oersteds method still used after 186 years ! -
Magnetic material, e.g iron
current
magnetic regions domains
26
Magnetism and Magnetic Materials today
the high-tech society
27
The spin on electronics magnetic devices in
computers
chip - RAM
disk
0 and 1 bits small magnetic areas with
opposite magnetization direction
28
Magnetic recording technology
Courtesy of Jan Thiele, Hitachi
29
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
30
Brightness of x-ray sources
smaller and faster
31
X-rays have come a long way
x-ray images then and now
0
1
bits
10,000 times smaller
1895 W. Röntgen, Würzburg
1993 Magnetic x-ray image
32
ALS
The Power of X-Rays
33
A Glimpse of the Future
exploring spin-electronics
spintronics
34
Beyond Oersteds method spin doctoring
The concept of a spin polarized current
copper
copper
electrons
magnetic atoms in iron
spin polarized current
spins
35
Spin currents a new way of magnetic switching
spin current acts like an Exchange field
electric current creates magnetic field
Oersted field
sensor layer
current
current
referencelayer
sensor layer
Weak, long range
Strong, short range
36
Switching of magnetic memory cells (MRAM)
cell to be switched
better switching by current in wire
switching by Oersted field around wire
current
current
37
X-ray microscopy image of spin injection structure
100 x 300 nm
x-ray image
x
y
leads for ns current pulses
Detector
38
Movie 1
39
X-Ray microscopy images of magnetization in
buried sensor layer
After current in one direction
After current in other direction
magnetization has complicated horseshoe state
40
Movie 2
41
Next time not cartoons but
real x-ray movies !
42
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...
43
Acknowledgements
Yves Acremann, SSRL Ann Mueller, SSRL Michael
Hyde, SLAC Science website http//www.howstuffwo
rks.com My research group http//www-ssrl.slac.s
tanford.edu/stohr http//www-ssrl.slac.stanford.e
du/stohrgroup New book J. Stöhr and H. C.
Siegmann Magnetism From Fundamentals to
Nanoscale Dynamics Springer Verlag,
February/March 2006
44
The end
45
Magnetic recording Small and fast !
1 mile/hour
1000 miles/hour
Incredibly small bits incredible writing and
reading speeds