Magnetic Flames in Molecular Magnets Exhibit
Properties Akin to Fire
(Source: City College of New York)
In a groundbreaking experiment, researchers from The City College of
New York (CCNY) and Lehman College have measured the speed of
magnetic avalanches and discovered that the process is analogous to
the flame front of a flammable substance. The discovery of a
“magnetic flame” could make it easier for engineers to study the
dynamics of fire.
Magnetic avalanches occur when the polarity of a molecular
nanomagnet is changed suddenly and sufficient energy is released to
cause a chain reaction that changes the polarity of the other
molecular nanomagnets in a crystal.
Yoko Suzuki, a graduate student at The City College, devised an
experiment to measure the progress of a molecular avalanche through
a crystal of Mn12 (manganese) acetate using an array of tiny
micrometer sized Hall sensors placed underneath the specimen. Ms.
Suzuki observed that the avalanche began at one end of the crystal
and propagated at speeds of a few meters per second in the form of a
“flame” front that released magnetic energy into the crystal.
 |
|
Computer simulation of a magnetic
avalanche. The boundary or "flame front" travels from top to
bottom, flipping magnetic spins from one direction (below the
boundary) to the other (above the boundary).
|
“Molecular nanomagnets are the first-known magnetic materials in
which the magnetic energy density is sufficient to ignite a
‘magnetic flame,’” said Dr. Myriam P. Sarachik, distinguished
professor of Physics at CCNY and Ms. Suzuki’s mentor. “This could
open a potentially important new road for investigating the dynamics
of fire in flammable substances because, unlike chemical burning,
magnetic burning is non-destructive, reversible and more readily
controlled.”
The investigation into the propagation of magnetic avalanches grew
out of a theory suggested by Eugene Chudnovsky and Dmitry Garanin.
Dr. Chudnovsky, distinguished professor of Physics at Lehman
College, collaborated with Ms. Suzuki and Professor Sarachik in the
present work.
Chudnovsky and Garanin had theorized that under the right
circumstances a magnetic system could be made to emit laser type
radiation. They suggested that a magnetic avalanche might initiate
such laser action. Measuring the speed of the avalanche would aid in
the examination of the theory.
When experimentalists at CCNY discovered that the avalanche
propagates at a constant speed of a few meters per second, Professor
Chudnovsky proposed that the effect is, in fact, “magnetic burning”.
Comparison between theory and experiment confirmed his conjecture.
A paper reporting the discovery of “magnetic burning” by Ms. Suzuki,
Professors Sarachik and Chudnovsky and coauthors has been accepted
for publication in Physical Review Letters. In addition to CCNY and
Lehman College, scientists from the Weizmann Institute in Israel and
the University of Florida participated in the project, providing the
Hall sensors and crystals, respectively.
For more information visit
www1.ccny.cuny.edu. |