Transcript 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