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New
Release -- Superconductor Week does not edit or endorse the following
news release: Freezing
magnets with magnets
Upton,
NY, Mar. 13: A "spin liquid" is a very unique, dynamic material in which each
spin – the tiny magnetic field carried by an electron – is not frozen into
place, producing clearly defined magnetic regions. Instead, the spins are free
to change orientation. Because of this, external magnetic fields applied to spin
liquids may produce changes that even extreme temperatures and pressures cannot.
Jason
Gardner, a scientist at the U.S. Department of Energy's
Brookhaven National
Laboratory and the National
Institute of Standards and Technology, has been able to freeze a spin liquid
by applying a magnetic field. This liquid-to-solid transition (like water to
ice) allowed Gardner and his colleagues to reveal an unusual property of a spin
liquid system -- a property that may hold the key to understanding this unusual
magnetic state and how it could be used to better understand superconductivity.
"Regular
liquids are expected to crystallize at low temperatures," Gardner said. "A spin
liquid should too, but the system I'm studying remains a liquid down to
temperatures close to absolute zero, the coldest temperature possible."
Gardner
will discuss this research at the March meeting of the American Physical Society
in Baltimore, Maryland. His talk will take place at 3:42 pm on March 13, in room
307 of the Baltimore Convention Center.
Spin
liquids are found in several magnetic materials, including high-temperature
superconducting materials, however Gardner studies this exotic magnetic state in
materials that exhibit geometrical frustration. This occurs when the geometry of
the material's atomic lattice and the magnetic interactions within the material
are incompatible. In his most recent study, he examined an insulating material
consisting of the elements terbium (Tb), titanium (Ti), and oxygen (O).
Abbreviated Tb2Ti2O7, this material remains in a spin liquid state at extreme
low temperatures, but begins to crystallize under extremely high pressure
(100,000 times atmospheric pressure) and now, as Gardner and his group have
discovered, under magnetic fields.
"Tb2Ti2O7
is a bit of a mystery in frustrated magnetism," Gardner said. "It remains very
dynamic down to 17 milli-Kelvin (absolute zero is 0 Kelvin), but theory states
that it should freeze at temperatures 1000 times higher. Fully understanding
this magnet will bring new insight into other dynamic systems, not only spin
liquids."
The
second part of Gardner's talk will center on the "neutron spin echo technique,"
a new area of research in frustrated magnetism. This technique uses neutrons to
measure the slow motions of atoms, molecules, and magnetic spins on very short
timescales -- as small as nanoseconds (billionths of a second) and even
picoseconds (trillionths of a second). It works by measuring the very subtle
change in speed of a neutron as it interacts with matter. It has been applied to
problems in biology, chemistry and physics including how oil and water interact
and how polymer chains vibrate.
"The
neutron spin echo facility at the Center for Neutron Research at NIST is unique
in the Americas," Gardner said. "In collaboration with Georg Ehlers at the
Spallation Neutron Source at Oak Ridge National Laboratory, we have been doing
some great work on the slow dynamics in frustrated magnets." Gardner and his
colleagues hope that their studies will encourage others to use this facility.
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