Magnetic 'handedness' could lead to better magnetic storage devices
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ARGONNE, Ill. (May 25, 2007) – Better magnetic storage devices for computers
and other electronics could result from new work by researchers in the
United States and Germany.
Their findings demonstrate that chirality – a spiral-like "handedness" – in
nanoscale magnets may play a crucial role in data transmission and manipulation
in spintronic devices, where the spin rather than the charge of an electron
is used to store data.
While the spins in ferromagnetic materials are simply oriented along one common
direction, some nanomagnets were found to exhibit chirality. The term chirality
refers to objects that differ from their mirror image like the human hand.
Matthias Bode, a scientist at the Center
for Nanoscale Materials at Argonne
National Laboratory, said, “In nature many systems have chirality, such as
elementary particles with electro-weak interactions organic molecules, hurricanes
and even galaxies. Solids with magnetic order of unique chirality are prime
candidates for applications, because their peculiar symmetry allows the mixing
of electronic, optic, magnetic and structural properties.”
The researchers used spin-sensitive scanning tunneling miscroscopy (STM) and
first-principles electronic structure calculations to identify the magnetic
order. By making the STM technique sensitive to the spin, it allowed for the
observation of the magnetism of single atoms. This extension of STM is known
as spin polarized STM or SP-STM and was developed by Bode.
Using his enhanced technique, Bode demonstrated that under a magnetic field
the pattern shifted in a given direction, which identified the unique chirality.
Results of the research were published in the May
10 issue of the journal Nature.
The premise for this work was inspired by the pioneering effort of Soviet
physicist, Igor Dzyaloshinski. He showed that magnetic order may get twisted
into helices with long-period in crystals lacking inversion symmetry, if the
spin-orbit interactions are strong enough.
“In the past, this interaction had been considered unimportant in the scientific
community," Bode said. "Now its relevance in nanostructures of any
dimensionality such as thin films or magnetic particles is realized.”
Other researchers involved in this study are M. Heide, G. Bihlmayer and S.
Blugel of Julich, Germany and K. von Bergmann, P. Ferriani, S. Heinze, A.
Kubetzka, O. Pietzsch and R. Wiesendanger of Institute of Applied Physics and
Microstructure Research Center, University
of Hamburg, Hamburg, Germany.
Funding for this work was provided by the German Science Foundation.
Other Argonne research recently featured in Nature was conducted by
Oleg Shpyrko, Eric Isaacs and their colleagues at the University of Chicago. Their findings led to a major breakthrough in the understanding of antiferromagnets.
By exploiting a technique called “X-ray photon correlation spectroscopy, the
researchers were able to see the internal workings of antiferromagnets, such
as the metal chromium, for the very first time, thus bringing into focus previously
invisible phenomena.
In addition to producing the first holograms of an antiferromagnet, the research
revealed that the holograms are actually time-dependent, even down to the lowest
temperatures. This implies that the antiferromagnet is never truly at rest,
and the responsibility for this most likely lies with quantum mechanics and
the uncertainties it imposes not only on conventional particles such as electrons
and atoms, but also on objects such as domain walls in magnets. The new experiments
thus help to open the prospect of exploiting antiferromagnets in emerging technologies
such as quantum computing.
Work on this project at the Center for Nanoscale Materials and the Advanced
Photon Source was supported by the Department of Energy's Office of Science,
Office of Basic
Energy Sciences. Work at the London
Centre for Nanotechnology was funded by a Royal Society Wolfson
Research Merit Award and the Basic Technologies
program of Research
Councils United Kingdom. Work at the University
of Chicago was supported by the National
Science Foundation.
The results of this research can be found in the May
3 issue of Nature.
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For more information, please
contact Steve McGregor (630/252-5580 or media@anl.gov)
at Argonne.
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