A novel material that may demonstrate a highly unusual"liquid" magnetic state at extremely low temperatures has beendiscovered by a team of Japanese and U.S. researchers, according totomorrow's issue of Science.*
The material, nickel galliumsulfide (NiGa2S4), was synthesized by scientists at Kyoto University.Its properties were studied by both the Japanese team and byresearchers from The Johns Hopkins University (JHU) and the Universityof Maryland (UM) at the Commerce Department's National Institute ofStandards and Technology (NIST).
The scientists studied thepolycrystalline sample using both X-rays and neutrons as probes tounderstand its structure and properties. The neutron experiments wereconducted at the NIST Center for Neutron Research.
The team foundthat the triangular arrangement of the material's atoms appears toprevent alignment of magnetic "spins," the characteristic of electronsthat produces magnetism. A "liquid" magnetic state occurs when magneticspins fluctuate in a disorderedly, fluid-like arrangement that does notproduce an overall magnetic force. The state was first proposed astheoretically possible about 30 years ago. A liquid magnetic state maybe related to the similarly fluid way that electrons flow withoutresistance in superconducting materials.
According to CollinBroholm, a professor in the Department of Physics and Astronomy at TheJohns Hopkins University in Baltimore, "the current work shows that atan instant in time the material looks like a magnetic liquid, butwhether there are fluctuations in time, as in a liquid, remains to beseen."
Each electron can be thought of as a tiny bar magnet. Thedirection of its "north" pole is its spin. "An ordered pattern of spinsgenerally uses less energy," says Broholm, "but the triangular crystalstructure prevents this from happening in this material."
Theteam conducted their neutron experiments with an instrument called a"disk chopper spectrometer." The only one of its kind in North America,the instrument sends bursts of neutrons of the same wavelength througha sample. Then, more than 900 detectors arranged in a large semicircledetermine exactly where and when the neutrons emerge, providinginformation key to mapping electron spins.
"The energy range andresolution we can achieve with this instrument is ideal for studyingmagnetic systems," adds Yiming Qiu, a NIST guest researcher from UM.
Thewavelength of the slowed-down (cold) neutrons available at the NISTfacility--less than 1 nanometer (billionth of meter)--also allows theresearchers to study nanoscale magnetic properties too small to bemeasured with other methods.
The project was funded byGrants-in-Aid for Scientific Research from the Japan Society for thePromotion of Science and for the 21st Century Center of Excellence''Center for Diversity and Universality in Physics'' from MEXT ofJapan, and by the Inamori Foundation. Work at The Johns HopkinsUniversity was supported by the U.S. Department of Energy. Work at NISTwas supported in part by the National Science Foundation.
As anon-regulatory agency, NIST develops and promotes measurement,standards and technology to enhance productivity, facilitate trade andimprove the quality of life.
* S. Nakatsuji, Y. Nambu, H. Tonomura,O. Sakai, S. Jonas, C. Broholm, H. Tsunetsugu, Y. Qiu, Y. Maeno. "SpinDisorder on a triangular lattice." Science, Sept. 9, 2005.
Materials provided by National Institute of Standards and Technology (NIST). Note: Content may be edited for style and length.
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