Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Researchers Say ’Frustrated Magnets’ Hint at Broader Organizing Principle in Nature

27.08.2002


When "frustrated" by their arrangement, magnetic atoms surrender their individuality, stop competing with their neighbors and then practice a group version of spin control—acting collectively to achieve local magnetic order—according to scientists from the Commerce Department’s National Institute of Standards and Technology, Johns Hopkins University and Rutgers University writing in the Aug. 22, 2002, issue of the journal Nature.


Chill! Atoms in zincochromite, a "geometrically frustrated magnet," resolve their frustration through group spin control. Neighboring tetraheda (solids with four triangular faces) contribute a side each to create hexagonal (six-sided) spin clusters. A hexagon bunches the spins of magnetic atoms-one at each corner-into a single "spin director" (arrows). The composite behavior achieves local magnetic order.



The unexpected composite behavior detected in experiments done at the NIST Center for Neutron Research (NCNR) accounts for the range of surprising—and, heretofore, unexplainable—properties of so-called geometrically frustrated magnets, the subject of intensifying research efforts that may lead to new types of matter. The finding also may shed light on natural clustering processes including the assembly of quarks and other minuscule components into atoms, the folding of proteins and the clumping of stars in galaxies, the scientists say.

These and other important phenomena—including high-temperature superconductivity—suggest that there are "higher-order organizing principles that are intrinsic to nature," explains lead author Seung-Hun Lee, NCNR staff physicist.


The team discovered that self-organized "spin clusters" emerge out of competing interactions in a geometrically frustrated magnet. Though involving interactions on a very tiny scale—measured in nanometers (billionths of a meter)—the team says its discovery may provide a new model for exploring "emergent structure in complex interacting systems" on different levels. They singled out research on protein folding as a potential beneficiary. In protein folding, cells assemble units called amino acids into complex three-dimensional shapes that dictate the function of the resulting protein.

Lee and colleagues set out to determine how atoms arrayed in the lattice—like geometry of frustrated magnets resolve an apparent predicament: how to align their spins-the sources of magnetism—when faced with a bewildering number of options.

As a conventional magnet cools, atoms pair up with their neighbors and line up their spins, so that they spin in parallel or in opposition (antiparallel). At a temperature unique to the type of material, the magnet undergoes a phase transition, at which a highly symmetrical, long-range ordering of spins is achieved. The material and each spin are said to be in their ground state, a condition of equilibrium, or ultimate stability.

For illustration, this spin-ordering is accomplished easily in materials with squares as a structural building block. An atom can spin antiparallel to the spins of the atoms in the two adjacent corners.

This is not the case for a geometrically frustrated magnet, which is assembled from triangular units. If atoms at two corners spin antiparallel, the atom in the third is left with a no-win situation. Whichever orientation it chooses, the third atom will be out of sync with one of its two neighbors. As a result, the entire system is "geometrically frustrated" and all spins can fluctuate among a range of potential ground states. Long-range order is not attainable, raising the question as to how spins organize locally to cope with a seemingly confusing array of alignment options.

At the NCNR, researchers used neutrons, which are sensitive to magnetic spins, to probe magnetic interactions in zincochromite, a mineral whose crystal structure consists of tetrahedral building blocks with four triangular faces. Beams of neutrons can serve as a high-power magnetic microscope that reveals the geometric arrangement of spins in a solid and how this arrangement evolves as temperature changes. Patterns of neutrons that scattered after they were beamed at zincochromite samples revealed orderly groupings of spins.

The researchers determined that, at low temperatures, the spins organize into six-sided, or hexagonal, structures that repeat throughout the material. Six neighboring tetrahedra contribute one side each to the hexagon. In turn, six spins, one at each corner, are arranged so that each one is antiparallel to its two nearest neighbors—a highly stable organization.

The patterns of scattered neutrons also suggest that the six hexagon spins act in concert, bunching all spins into one and creating what Lee and his colleagues call a "spin director." Each hexagon achieves local magnetic order and its spin director is largely confined, interacting only weakly with the spin directors of neighboring hexagons.


As a result, the researchers say, geometrically frustrated magnets are not, as suspected, a system of strongly interacting spins, but rather a "protectorate of weakly interacting" composite spins.

In addition to Lee, collaborators include Collin Broholm of Johns Hopkins University and the NCNR; William Ratcliff of Rutgers University; Goran Gasparovic of Johns Hopkins; Qing Zhen Huang of the NCNR; Tae Hee Kim of Rutgers; and Sang-Wook Cheong of Rutgers.

As a non-regulatory agency of the U.S. Department of Commerce’s Technology Administration, NIST develops and promotes measurements, standards, and technology to enhance productivity, facilitate trade and improve the quality of life.

Mark Bello | EurekAlert!
Further information:
http://www.nist.gov/

More articles from Physics and Astronomy:

nachricht Meteoritic stardust unlocks timing of supernova dust formation
19.01.2018 | Carnegie Institution for Science

nachricht Artificial agent designs quantum experiments
19.01.2018 | Universität Innsbruck

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Artificial agent designs quantum experiments

On the way to an intelligent laboratory, physicists from Innsbruck and Vienna present an artificial agent that autonomously designs quantum experiments. In initial experiments, the system has independently (re)discovered experimental techniques that are nowadays standard in modern quantum optical laboratories. This shows how machines could play a more creative role in research in the future.

We carry smartphones in our pockets, the streets are dotted with semi-autonomous cars, but in the research laboratory experiments are still being designed by...

Im Focus: Scientists decipher key principle behind reaction of metalloenzymes

So-called pre-distorted states accelerate photochemical reactions too

What enables electrons to be transferred swiftly, for example during photosynthesis? An interdisciplinary team of researchers has worked out the details of how...

Im Focus: The first precise measurement of a single molecule's effective charge

For the first time, scientists have precisely measured the effective electrical charge of a single molecule in solution. This fundamental insight of an SNSF Professor could also pave the way for future medical diagnostics.

Electrical charge is one of the key properties that allows molecules to interact. Life itself depends on this phenomenon: many biological processes involve...

Im Focus: Paradigm shift in Paris: Encouraging an holistic view of laser machining

At the JEC World Composite Show in Paris in March 2018, the Fraunhofer Institute for Laser Technology ILT will be focusing on the latest trends and innovations in laser machining of composites. Among other things, researchers at the booth shared with the Aachen Center for Integrative Lightweight Production (AZL) will demonstrate how lasers can be used for joining, structuring, cutting and drilling composite materials.

No other industry has attracted as much public attention to composite materials as the automotive industry, which along with the aerospace industry is a driver...

Im Focus: Room-temperature multiferroic thin films and their properties

Scientists at Tokyo Institute of Technology (Tokyo Tech) and Tohoku University have developed high-quality GFO epitaxial films and systematically investigated their ferroelectric and ferromagnetic properties. They also demonstrated the room-temperature magnetocapacitance effects of these GFO thin films.

Multiferroic materials show magnetically driven ferroelectricity. They are attracting increasing attention because of their fascinating properties such as...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

10th International Symposium: “Advanced Battery Power – Kraftwerk Batterie” Münster, 10-11 April 2018

08.01.2018 | Event News

See, understand and experience the work of the future

11.12.2017 | Event News

Innovative strategies to tackle parasitic worms

08.12.2017 | Event News

 
Latest News

Let the good tubes roll

19.01.2018 | Materials Sciences

How cancer metastasis happens: Researchers reveal a key mechanism

19.01.2018 | Health and Medicine

Meteoritic stardust unlocks timing of supernova dust formation

19.01.2018 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>