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11-11/12 :: November/December 2011
nanotimes News in Brief
treatments, including, critically, one in which the alloy was heated to an annealing temperature and then suddenly quenched in water.
Quenching is a classic metallurgy technique to freeze a material‘s microstructure in a state that it normally only has when heated. In this case, measurements at NIST and the Stanford Synchrotron Radiation Lightsource (SSRL) showed that the best-performing alloy had a delicate hetereogenous, nanoscale struc- ture in which cobalt-rich crystals were embedded throughout a different, iron-rich crystal structure. Magnetostriction was determined by measuring the amount by which the alloy bent the tiny silicon can- tilever in a magnetic field, combined with delicate measurements at NIST to determine the stiffness of the cantilever.
The best annealed alloy showed a sizeable magne- tostriction effect in magnetic fields as low as about 0.01 Tesla. (The earth‘s magnetic field generally ranges around roughly 0.000 045 T, and a typical ferrite refrigerator magnet might be about 0.7 T.)
The results, says team leader Ichiro Takeuchi of UMd, are lower than, but comparable to, the values for the best known magnetostrictive material, a rare- earth alloy called Tb-Dy-Fe (Terbium-Dysprosium- Iron) – but with the advantage that the new alloy doesn‘t use the sometimes difficult to acquire rare earths. “Freezing in the heterogeneity by quenching is an old method in metallurgy, but our approach may be unique in thin films,” he observes. “That‘s the beauty – a nice, simple technique but you can get these large effects.”
The quenched alloy might offer both size and proces-
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sing advantages over more common piezoelectric mi- crodevices, says NIST materials scientist Will Osborn. “Magnetorestriction devices are less developed than piezoelectrics, but they‘re becoming more interesting because the scale at which you can operate is smal- ler,” he says. “Piezoelectrics are usually oxides, brittle and often lead-based, all of which is hard on manufacturing processes. These alloys are metal and much more compatible with the current generation of integrated device manufacturing. They‘re a good next-generation material for microelectromechanical machines.”
The effort also involved researchers from the Russian Institute of Metal Physics, Urals Branch of the Acade- my of Science; Oregon State University and Rowan University. Funding sources included the Office of Naval Research and the National Science Founda- tion. SSRL is part of the SLAC National Accelerator Laboratory, operated under the auspices of the U.S. Department of Energy.
D. Hunter, W. Osborn, K. Wang, N. Kazantseva, J. Hat- trick-Simpers, R. Suchoski, R. Takahashi, M.L. Young, A. Mehta, L.A. Bendersky, S.E. Lofland, M. Wuttig and I. Ta- keuchi: Giant magnetostriction in annealed Co1
-x Fex thin-
films, In: Nature Communications, Vol. 2, Article number: 518, November 1, 2011, DOI:10.1038/ncomms1529: http://dx.doi.org/10.1038/ncomms1529