2-D magnetism reaches a new milestone

phys.org | 1/21/2019 | Staff
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Researchers at the Center for Correlated Electron Systems, within the Institute for Basic Science (IBS) in South Korea, in collaboration with Sogang University and Seoul National University, reported the first experimental observation of a XY-type antiferromagnetic material, whose magnetic order becomes unstable when it is reduced to one-atom thickness. Published in Nature Communications, these findings are consistent with theoretical predictions dating back to the 1970s.

Dimensionality in physics is an important concept that determines the nature of matter. The discovery of graphene opened the doors of the 2-D world: a place where being one-atom or two-atom thick makes a difference. Since then, several scientists became interested in experimenting with 2-D materials, including magnetic materials.

Materials - Spin - Behavior - Spins - Ferromagnets

Magnetic materials are characterized by their spin behavior. Spins can be aligned parallel or antiparallel to each other, resulting in ferromagnets or antiferromagnets, respectively. Beyond that, all class of materials can, in principle, belong to three different models according to some fundamental understanding of physics: Ising, XY or Heisenberg. The XY model explains the behavior of materials whose spins move only on a plane consisting of the x and y axis.

Spin behavior can dramatically change upon slicing down the magnet to its thinnest level, as 2-D materials are more sensitive to temperature fluctuations, which can destroy the pattern of well-aligned spins. Almost 50 years ago, John M. Kosterlitz and David J. Thouless, and Vadim Berezinskii independently, described theoretically that 2-D XY models do not undergo a normal magnetic phase transition at low temperatures, but a very unusual form, later called BKT transition. They realized that quantum fluctuations of individual spins are much more disruptive in the 2-D world than in the 3-D one, which can lead to spins taking a vortex pattern. Kosterlitz and Thouless were awarded the Nobel Prize in Physics in 2016.

Years - Materials

Over the years, ferromagnetic materials...
(Excerpt) Read more at: phys.org
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