May 31 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.