UpDate - Vol. 16, No. 14
December 12, 1996
Physicist coordinated prestigious think tank
Just as he combines permanent or "hard" magnets with "soft"
or temporary ferromagnetic materials to create super-strong,
lightweight magnets, George Hadjipanayis, physics and astronomy,
brought opposing camps of researchers together last summer for a
prestigious international think tank exploring magnetic
phenomena.
Hadjipanayis, who heads a $2.3 million Department of Defense-
sponsored Multidisciplinary University Research Initiative (MURI)
on magnetic materials, was invited to direct an Advanced Study
Institute in Mykonos, Greece. Sponsored by the North Atlantic
Treaty Organization (NATO), the U.S. Army, the U.S. Department of
Energy and the UD Department of Physics and Astronomy, the July 1-
12 event gave researchers studying hard ferromagnetic materials
and magnetic recording media a rare opportunity to compare notes
with those focusing on soft magnets. It also gave students a
chance to learn from leading magnetics experts.
"In organizing this event, I wanted to help educate students
to succeed in this field," Hadjipanayis, a native of Cyprus who
received his doctoral degree from the University of Manitoba,
Canada, said. "The students heard presentations by some very big-
name scientists. They even got to play a little volleyball with
them."
Departmental colleagues Patricia K. Musa and Helen Long
provided administrative support during the event. When asked what
she thought of the island of Mykonos, Long emphatically offered
this two-word description: "It's fabulous." Mykonos is surrounded
by the crystal-clear green and blue waters of the Aegean Sea. She
said the residents live in quaint white houses with trim painted
to match the colors of the ocean. Gentle trade winds provide
"natural air-conditioning," Hadjipanayis added.
One of the first researchers to develop strong, iron-rich
neodymium-iron-boron (Nd-Fe-B) magnets prepared by heating and
then cooling rare earth-iron compounds, Hadjipanayis has directed
two previous NATO Advanced Study institutes.
"Each year, NATO sponsors several of these institutes on
topics of current scientific interest," Henry Glyde, physics and
astronomy chairperson, said. "These events are held in a NATO
country and attended by world experts as well as a select number
of graduate students representing NATO and different countries.
By selecting George to direct this latest institute, NATO
recognized his many accomplishments and his role as a leading
expert in the field of magnetics research. It's a great honor for
the University to have a faculty member who was selected to
direct not one, but three institutes."
The most recent Advanced Study Institute focused on a
phenomenon known as magnetic hysteresis, which provides
fundamental information about a material's magnetic properties.
Magnetism occurs within atoms when electrons revolve around
a nucleus while also spinning on their own axes-just as spinning
planets circle the Sun in our solar system, Hadjipanayis
explained. Both of these motions (and especially the spinning)
produce a magnetic force. In most materials, electrons are
arranged so that their movements "cancel each other out, creating
no net magnetism," Hadjipanayis said. But no cancellation occurs
in ferromagnets, and a magical interaction between the electrons
of neighboring atoms aligns their spinning, making them point in
the same direction and producing a large magnetic force
throughout the material.
If no magnetic field is present, Hadjipanayis said,
ferromagnetic materials exhibit no magnetic strength, although
their electrons are aligned and spinning.
In the absence of a magnetic field, it seems, different
domains are magnetized in different directions, resulting in zero
magnetization. When an external magnetic field is applied, the
domain walls shift to align the spins of all electrons within
every domain.
In soft magnets, the domain walls move easily, Hadjipanayis
said, whereas they're more resistant to change in hard magnets.
Consequently, the strength of the magnetic field needed to
"coerce" or demagnetize a material can serve as a measure of its
hardness.
Because soft magnets can easily be "switched off and on," or
demagnetized, they're used in electrical transformers, which
convert an AC (alternating current) voltage to a lower or higher
value, Hadjipanayis said. On the other hand, hard magnets are
difficult to demagnetize, making them suitable for devices
requiring a constant magnetic field, such as motors and
generators. Hard magnets also may be found in many "hidden"
applications, such as automobiles, which require magnets for 25
different functions, and in VCRs and computers, Hadjipanayis
said. Semi-hard magnets, incorporating qualities of both hard and
soft magnets, are ideal for use in magnetic recording media, he
said.
Hadjipanayis directs several campus efforts to develop more
powerful and less expensive magnets. Lately, he has been trying
to combine the strength of hard magnets with the efficiency and
versatility of soft magnets. For example, his team is mixing, on
the nanometer scale, particles of an inexpensive, soft magnetic
material (iron) with stronger but more costly rare-earth magnetic
particles.
"We are developing a new type of less expensive magnet that
could be useful in the automobile industry," he explained.
"Currently, many magnets in cars are made of ferrite. Ferrites
are not very strongly magnetic, so you have to use a large piece
of the material. A rare-earth magnet would allow you to
miniaturize these components, but they would be too expensive for
use in cars."
Hadjipanayis also develops special microstructures composed
of magnetic particles grown from vapor. If the process can be
more precisely controlled, he said, highly magnetic and isolated
particles smaller than 10 nanometers could reduce magnetic
interference on recording disks, making it possible to store more
information, perhaps with a density greater than 10 billion bits
per square inch.
Finally, Hadjipanayis and his colleagues are making films
composed of many alternating nanometer-scale layers of hard and
soft magnets, for use in magneto-electric applications, such as
computer components.
-Ginger Pinholster