mix strengthens magnet
Technology Research News
Work on the nanoscale doesn't have to produce
microscopic devices in order to come up with big results.
Researchers from IBM and the Georgia Institute of Technology have caused
4-nanometer metal particles to combine in a way that increases the strength
of magnets used in tiny, though not necessarily microscopic, electronic
devices. A nanometer is one millionth of a millimeter, or the length of
40 hydrogen atoms.
Permanent magnets are a key element of electric motors, generators, loudspeakers,
magnetic separators and magnetic levitation systems, and electric motors
are particularly important in small-scale applications. Using stronger
permanent magnets could reduce the size of these motors considerably,
said Shouheng Sun, a materials scientist at IBM Research.
The researchers' approach melds nanoparticles made from a pair of iron-platinum
compounds into a composite magnet that is potentially 50 percent stronger
than non-composite iron-platinum compounds, said Sun. The increase in
the available energy of the material means the magnet can carry out more
work than a similar-size non-composite magnet.
The key to the composite's strength is that the two compounds have different
magnetic properties: one is a hard-phase magnet and the other is a soft-phase
magnet. Hard-phase magnets hold their own, but aren't very strong: they
resist being demagnetized or reoriented by an external magnetic field
but tend to have weak magnetic fields. Soft-phase magnets are just the
opposite. They tend to have strong magnetic fields but those fields can
be easily demagnetized or reoriented by relatively small external magnetic
Coupling hard- and soft-phase materials so their magnetic orientations
line up produces an exchange-spring magnet, said Sun. This combination
of magnetic resilience and strength harbors more useful available energy,
The researchers made the material by mixing iron-platinum nanoparticles
and iron oxide nanoparticles in liquid, causing the nanoparticles to combine
by evaporating the liquid, then heating the nanoparticles to 650 degrees
Celsius. The heat converted the iron oxide to iron, which mixed with some
of the platinum to produce a pair of iron-platinum compounds with different
amounts of iron, and different magnetic properties. One material was hard-phase
and the other soft-phase. The heat also sintered, or partially blended,
the two compounds into an exchange-spring magnet.
This self-assembly process, which causes microscopic bits of material
to automatically line up particle by particle, is key when the particles
involved are so small. It's hard to make nanoscale composite materials
using conventional approaches, said Sun. "With self-assembly, we can start
with nano-sized components and engineer them into useful nanostructures,"
Exchange-spring magnets are an important new class of permanent magnets,
said Caroline Ross, an associate professor of materials science and engineering
at the Massachusetts Institute of Technology. This type of magnet has
a very high energy product, which makes it ideal for applications like
small motors where you need a strong magnet with a minimum volume, she
The researchers have shown that nanoparticle synthesis can produce very
good exchange-spring magnets, "at least on the small-scale available in
the experiment," said Ross. "The key to making these commercially useful
is to be able to produce the material in large enough quantities," she
The researchers' next step is to control the material's easy-axis orientation,
said Sun. A material's easy axis is the direction along which its magnetic
field prefers to line up. Controlling the orientation of the easy axis
would increase the energy product and thus the strength of the magnet
several times, he said.
The nanocomposite self-assembly method could be used to make practical
devices within five years, said Sun.
The researchers also plan to use the self-assembly technique to make other
kinds of nanocomposite materials for use in data storage and microwave
devices, said Sun.
Sun's research colleagues were Hao Zeng of IBM Research and Louisiana
Tech University, Jing Li of Louisiana Tech, and J. P. Liu and Zhong Wang
of Georgia Institute of Technology. They published the research in the
November 28, 2002 issue of Nature. The research was funded by the Defense
Advanced Research Projects Agency (DARPA) and IBM.
Timeline: <5 years
Funding: Government, Corporate
TRN Categories: Materials Science and Engineering
Story Type: News
Related Elements: Technical paper, "Exchange-Coupled Nanocomposite
Magnets by Nanoparticle Self-assembly," Nature, November 28, 2002
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