Freezing Magnets With Magnets

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 discussed this research at the March meeting of the American Physical Society in Baltimore, Maryland.

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.

Source: Brookhaven National Laboratory

Related stories:

New stem cell tools to aid drug development
SCIENTISTS have designed, developed and tested new molecular tools for stem cell research to direct the formation of certain tissue types for use in drug development programmes.
Stanford's 'autonomous' helicopters teach themselves to fly
Stanford computer scientists have developed an artificial intelligence system that enables robotic helicopters to teach themselves to fly difficult stunts by watching other helicopters perform the same maneuvers. The result is an autonomous helicopter than can perform a complete airshow of complex tricks on its own.
Integral locates origin of high-energy emission from Crab Nebula
(PhysOrg.com) -- Thanks to data from ESA's Integral gamma-ray observatory, scientists have been able to locate where particles in the vicinity of the rotating neutron-star in the Crab Nebula are accelerated to immense energies.
Magnetism and Superconductivity Observed to Exist in Harmony
(Physorg.com) -- Physicists at Los Alamos National Laboratory, along with colleagues at institutions in Switzerland and Canada, have observed, for the first time in a single exotic phase, a situation where magnetism and superconductivity are necessary for each other's existence.
Cell removal technique could lead to cheaper drugs
Researchers at the University of Edinburgh have pioneered a simple way to remove dead cells from cell cultures used to make protein-based drugs, which are increasingly prescribed to treat a range of illnesses.
Fast quantum computer building block created
(PhysOrg.com) -- The fastest quantum computer bit that exploits the main advantage of the qubit over the conventional bit has been demonstrated by researchers at University of Michigan, U.S. Naval Research Laboratory and the University of California at San Diego.
New Speed Record for Magnetic Memories
(PhysOrg.com) -- An experiment carried out at the Physikalisch-Technische Bundesanstalt (PTB) has realized spin torque switching of a nanomagnet as fast as the fundamental speed limit allows. Using this so-called ballistic switching future non-volatile magnetic memories could operate as fast as the fastest non-volatile memories. The experiments are described in the next issue of Physical Review Letters (22 August, 2008).
New theory for latest high-temperature superconductors
Physicists from Rice and Rutgers universities have published a new theory that explains some of the complex electronic and magnetic properties of iron "pnictides." In a series of startling discoveries this spring, pnictides were shown to superconduct at relatively high temperatures. The surprising discoveries created a great deal of excitement in the condensed matter physics community, which has been scrambling to better understand and document the unexpected results.

News discussion:

Physics news