Scientists spy Galfenol's inner beauty mark

Mar 25, 2009
NIST research collaboration spies Galfenol's inner beauty mark
Magnetostrictors are a critical element in sound detection equipment including the sonar used in submarines. Scientists working at NIST solved the structure of the magnetostrictor Galfenol, which could improve sonar's capabilities in the future. Credit: U.S. Navy photo

(PhysOrg.com) -- The sonar on submarines may get far more sensitive ears in the near future thanks to a mysterious compound developed by the military. Developed over a decade ago, it took a collaboration of scientists from the Virginia Polytechnic Institute and State University and the National Institute of Standards and Technology to determine why the material works. Surprisingly, the critical factor is a sprinkling of useful imperfections within an otherwise regular crystal.

The scientific team solved the internal structure of Galfenol, a compound of iron and that changes shape when exposed to a magnetic field. Because the effect also works in reverse—a tiny bit of pressure that distorts its shape slightly and induces detectable magnetism—such “magnetostrictors” are the key ingredients in sound detection equipment.

Iron alone has some talent as a magnetostrictor, but U.S. Navy researchers discovered in 1998 that doping iron with gallium amplifies iron’s magnetostrictive capability tenfold. They dubbed their creation Galfenol, but the basis for the material’s behavior went unexplained.

“It’s important to know why a material works the way it does,” says Peter Gehring of the NIST Center for Neutron Research (NCNR). “If you can relate its to its behavior, you might be able to improve the recipe.”

The scientists used neutron beams to determine Galfenol’s structure, settling a running debate over which model of its innards was correct. The investigation showed that the added gallium changes the structure of the iron, which on the forms a lattice of regular cubic cells. When the gallium combines with the iron, the faces of some cells become rectangular rather than square. These elongated gallium-iron cells then congregate into tiny clumps within the lattice, resembling “something like raisins within a cake,” as Gehring describes it.

The study also showed that these clusters of distorted cells respond to a magnetic field by rotating their magnetic moments, like tiny compass needles, to align with the field; it is this rotation that changes the exterior dimensions of the crystal. The clusters are thus responsible for Galfenol’s performance—it changes in size by 400 parts per million compared to iron’s 30—even though it seems surprising that imperfections in iron’s otherwise orderly lattice should improve its magnetostrictive talents.

“These irregularities give the iron more complex and richer properties,” Gehring says. “We see this theme repeated frequently in nature, where similar kinds of disorder lead to improved performance in high-temperature superconductors, giant magnetoresistive oxides, and other exotic new materials. It’s like the supermodel with a beauty mark on her cheek—we don’t know why it’s so appealing, but it is.

More information: * H. Cao, P.M. Gehring, C.P. Devreugd, J.A. Rodriguez-Rivera, J. Li and D. Viehland. The role of nano-scale precipitates on the enhanced magnetostriction of heat-treated Galfenol (Fe1-xGax) alloys. Physical Review Letters, forthcoming.

Provided by National Institute of Standards and Technology (news : web)

Explore further: Visualizing anisotropic carrier transport in organic semiconductor materials

Related Stories

New Nanoparticle Structure Boosts Magnetic Properties

Dec 19, 2005

Magnetic nanoparticles have shown promise as contrast-enhancing agents for improving cancer detection using magnetic resonance imaging (MRI), as miniaturized heaters capable of killing malignant cells, and as targeted drug ...

Recommended for you

What's fair?: New theory on income inequality

6 hours ago

The increasing inequality in income and wealth in recent years, together with excessive pay packages of CEOs in the U.S. and abroad, is of growing concern, especially to policy makers. Income inequality was ...

Scientists one step closer to mimicking gamma-ray bursts

12 hours ago

Using ever more energetic lasers, Lawrence Livermore researchers have produced a record high number of electron-positron pairs, opening exciting opportunities to study extreme astrophysical processes, such ...

Physicists solve quantum tunneling mystery

14 hours ago

An international team of scientists studying ultrafast physics have solved a mystery of quantum mechanics, and found that quantum tunneling is an instantaneous process.

How spacetime is built by quantum entanglement

14 hours ago

A collaboration of physicists and a mathematician has made a significant step toward unifying general relativity and quantum mechanics by explaining how spacetime emerges from quantum entanglement in a more ...

Experiment confirms quantum theory weirdness

14 hours ago

The bizarre nature of reality as laid out by quantum theory has survived another test, with scientists performing a famous experiment and proving that reality does not exist until it is measured.

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.