Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Scientists post a lower speed limit for magnetic switching

26.04.2004


The picture shows the 2 mile long linear accelerator as the background and the experiment and results superimposed as a schematic. The schematic shows the magnetic field surrounding the beam and the magnetic pattern (which is of micrometre size) written into a sample by the beam.


The speed of magnetic recording – a crucial factor in a computer’s power and multimedia capabilities – depends on how fast one can switch a magnet’s poles. An experiment at the Stanford Synchrotron Radiation Laboratory (SSRL) found that the ultimate speed of magnetic switching is at least 1,000 times slower than previously expected. The result, which appears in the April 22 issue of the journal Nature, has implications for future hard disk computer drive technologies.

In the push toward ever-faster magnetic recording, experts expected to find a physical limit, a threshold speed beyond which materials would respond chaotically. “If you had asked me a year ago, ‘How fast does one have to create a pulse that does not switch magnetization?’ my answer would have been one femtosecond (one thousandth of a trillionth of a second),” said Jo Stöhr, Deputy Director of SSRL. “Chaotic behavior was not expected in this experiment, which ran in the picosecond (trillionth-of-a-second) range.”

The SSRL is a division of the Stanford Linear Accelerator Center (SLAC), a U.S. Department of Energy (DOE) research facility operated by Stanford University. The collaboration for the Nature paper was led by SSRL scientists Hans Christoph Siegmann and Professor Joachim Stöhr , and included researchers from Seagate Technology, the world’s largest manufacturer of hard disk computer drives.



“This is a fascinating experiment that has given completely new information on the limits of magnetic switching,” said Raymond L. Orbach, director of the DOE Office of Science. “It is also a wonderful illustration of the value of very different disciplines working together: scientists from a synchrotron light source using a high energy physics linear accelerator to do an experiment on magnetism.”

Seagate’s Head of Media Research, Dieter Weller underlined, “This collaboration has evolved, over time, into a very fruitful exchange between academia and industry, Aligning ourselves with such high caliber people as Hans Christoph Siegmann and Jo Stöhr is a real feat for us.”

In a computer hard drive, a writing head hovers over a disk that’s rapidly spinning – at up to 15,000 rotations per minute, or 150 times faster than a CD player. An electric current running in the head creates a magnetic field, which records data by turning tiny areas of the disk’s surface into microscopic magnets. The disk is coated with a special, grainy material that allows only two, opposite directions of the magnetization, representing the 0 or 1 of a basic unit of data, or bit. High recording speed requires the coating material to respond and switch its poles quickly enough to record each bit reliably.

The experiment relied on the unique capabilities of SLAC’s 2-mile-long linear accelerator (linac). The beam of electrons produced by the linac played the role of the electric current in a hard drive’s writing head, based on the fact that moving electrons carry along a magnetic field that swirls around the electrons’ path. The idea came to Siegmann in the mid-1990’s, literally out of a lightning bolt: He realized that the linac could magnetically record the same way that a lightning leaves a magnetic signature when it strikes a rock.

The linac’s beam, made of tightly packed bunches of electrons traveling close to light speed, creates magnetic pulses that are some of the world’s strongest – at up to 10 Tesla, or 200,000 times the strength of the Earth’s magnetic field – and briefest, at 2 picoseconds (2 trillionths of a second).

The researchers shot up to seven electron bunches in a row through samples of magnetic recording media. In the photographs of the results, they expected to see dark and light areas, neatly arranged in concentric rings around the focus point of the beam. The two colors would correspond to grains magnetized in either of the two possible directions. Instead, the pictures showed all shades of grey, indicating that some grains had switched while others had not.

They observed similar results with different types of magnetic grains, or even with a continuous magnetic film. With the help of theoretical physicist Alexander Kashuba of the Landau Institute for Theoretical Physics in Moscow, the SSRL researchers realized that their data bore the signature of a chaotic system – one whose parts behave in a random, unpredictable way. “That’s the new thing,” said Siegmann. “It’s like roulette. You can’t tell in advance whether it will be dark or light.”

The challenge now will be to understand why the maximum speed seems to be at least 1,000 times lower than expected. The explanation, Siegmann said, could lie in the way thermal motion interacts with the magnetization process.

The limit on recording speed must be somewhere between 100 billion and a trillion bits per second, but is unlikely to ever affect technology, says Seagate’s Weller. State-of-the-art drives can now record about 1 billion bits per second, and long before that speed can be increased 100-fold, other physical constraints will get in the way, he says. In particular, higher speed requires smaller magnetic grains, but their size cannot go below the size of atoms.

The SSRL result could be an important step toward understanding the basic physics of data recording, leading to the development of entirely new technologies. A promising idea, Weller says, is heat-assisted recording, where a small section of the recording medium is temporarily brought to a high temperature, to speed up its magnetization reversal.

With the help of SLAC’s new Linac Coherent Light Source (LCLS), scheduled to start operating in 2008, researchers will be able to gain a solid understanding of the magnetic properties of matter. The LCLS will use the linac’s electron beam to produce laser-like X-ray pulses lasting just one femtosecond, enabling researchers to take snapshots of the magnetization process. “We will take images observing not only what has happened,” said Stöhr. “We will be able to see those processes while they happen.”

The DOE Office of Sciences both supported the research and funds the operation of the national user facilities at SLAC.

Neil Calder | SLAC
Further information:
http://www.slac.stanford.edu/slac/media-info/20040423/index.html
http://www-ssrl.slac.stanford.edu/
http://www.slac.stanford.edu/

More articles from Physics and Astronomy:

nachricht A new 'spin' on kagome lattices
10.12.2018 | Boston College

nachricht Supercomputers without waste heat
07.12.2018 | Universität Konstanz

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Researchers develop method to transfer entire 2D circuits to any smooth surface

What if a sensor sensing a thing could be part of the thing itself? Rice University engineers believe they have a two-dimensional solution to do just that.

Rice engineers led by materials scientists Pulickel Ajayan and Jun Lou have developed a method to make atom-flat sensors that seamlessly integrate with devices...

Im Focus: Three components on one chip

Scientists at the University of Stuttgart and the Karlsruhe Institute of Technology (KIT) succeed in important further development on the way to quantum Computers.

Quantum computers one day should be able to solve certain computing problems much faster than a classical computer. One of the most promising approaches is...

Im Focus: Substitute for rare earth metal oxides

New Project SNAPSTER: Novel luminescent materials by encapsulating phosphorescent metal clusters with organic liquid crystals

Nowadays energy conversion in lighting and optoelectronic devices requires the use of rare earth oxides.

Im Focus: A bit of a stretch... material that thickens as it's pulled

Scientists have discovered the first synthetic material that becomes thicker - at the molecular level - as it is stretched.

Researchers led by Dr Devesh Mistry from the University of Leeds discovered a new non-porous material that has unique and inherent "auxetic" stretching...

Im Focus: The force of the vacuum

Scientists from the Theory Department of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science (CFEL) in Hamburg have shown through theoretical calculations and computer simulations that the force between electrons and lattice distortions in an atomically thin two-dimensional superconductor can be controlled with virtual photons. This could aid the development of new superconductors for energy-saving devices and many other technical applications.

The vacuum is not empty. It may sound like magic to laypeople but it has occupied physicists since the birth of quantum mechanics.

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

New Plastics Economy Investor Forum - Meeting Point for Innovations

10.12.2018 | Event News

EGU 2019 meeting: Media registration now open

06.12.2018 | Event News

Expert Panel on the Future of HPC in Engineering

03.12.2018 | Event News

 
Latest News

Proteins imaged in graphene liquid cell have higher radiation tolerance

10.12.2018 | Materials Sciences

New Plastics Economy Investor Forum - Meeting Point for Innovations

10.12.2018 | Event News

A new molecular player involved in T cell activation

07.12.2018 | Life Sciences

VideoLinks
Science & Research
Overview of more VideoLinks >>>