NIST research collaboration spies Galfenol's inner beauty mark

March 25, 2009

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 (NIST) 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 gallium 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 atomic structure 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 atomic level 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.
The study was funded in part by the Office of Naval Research.

* 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.

National Institute of Standards and Technology (NIST)

Related Magnetic Field Articles from Brightsurf:

Investigating optical activity under an external magnetic field
A new study published in EPJ B by Chengping Yin, Guangdong Provincial Key Laboratory of Quantum Engineering and Quantum Materials, South China, aims to derive an analytical model of optical activity in black phosphorous under an external magnetic field.

Magnetic field and hydrogels could be used to grow new cartilage
Instead of using synthetic materials, Penn Medicine study shows magnets could be used to arrange cells to grow new tissues

Magnetic field with the edge!
This study overturns a dominant six-decade old notion that the giant magnetic field in a high intensity laser produced plasma evolves from the nanometre scale.

Global magnetic field of the solar corona measured for the first time
An international team led by Professor Tian Hui from Peking University has recently measured the global magnetic field of the solar corona for the first time.

Magnetic field of a spiral galaxy
A new image from the VLA dramatically reveals the extended magnetic field of a spiral galaxy seen edge-on from Earth.

How does Earth sustain its magnetic field?
Life as we know it could not exist without Earth's magnetic field and its ability to deflect dangerous ionizing particles.

Scholes finds novel magnetic field effect in diamagnetic molecules
The Princeton University Department of Chemistry publishes research this week proving that an applied magnetic field will interact with the electronic structure of weakly magnetic, or diamagnetic, molecules to induce a magnetic-field effect that, to their knowledge, has never before been documented.

Origins of Earth's magnetic field remain a mystery
The existence of a magnetic field beyond 3.5 billion years ago is still up for debate.

New research provides evidence of strong early magnetic field around Earth
New research from the University of Rochester provides evidence that the magnetic field that first formed around Earth was even stronger than scientists previously believed.

Massive photons in an artificial magnetic field
An international research collaboration from Poland, the UK and Russia has created a two-dimensional system -- a thin optical cavity filled with liquid crystal -- in which they trapped photons.

Read More: Magnetic Field News and Magnetic Field Current Events is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to