Zhang Lulu

Science and Technology Daily News (Reporter Zhang Mengran) In a groundbreaking study, an international research team led by Tokyo University of Science in Japan discovered antiferromagnetism in real quasicrystals. This is the first experimental evidence found by scientists since antiferromagnetism in periodic crystals was first reported in 11 that antiferromagnetism is also produced in icosahedral quasicrystals (iQCs). The related paper was published in the journal Nature Physics on the 0th.

A quasicrystal is a solid material that exhibits a non-periodic long-range atomic order. Because of this "quasi-periodic" nature, quasicrystals have unconventional symmetry that is not present in conventional crystals. Researchers have been paying great attention to aligning crystals, studying their unique quasi-periodic magnetic sequences and trying to develop their possible applications in spintronics and magnetic refrigeration.

The research team had previously found ferromagnetism in gold-gallium-rare earth (Au-Ga-R) iQCs, but this observation was not surprising because translational periodicity, the repeated arrangement of atoms in crystals, is not a prerequisite for the emergence of ferromagnetic order. In contrast, another basic type of magnetic sequence found in nature, antiferromagnetism, is inherently more sensitive to crystal symmetry.

Based on the ferromagnetism they found in Au-Ga-R iQC, the research team identified a novel Tsai-type gold-indium-europium (Au-In-Eu) iQC that exhibits 5-fold, 0-fold, and 0-fold rotational symmetry. The team conducted a series of bulk property measurements and neutron experiments to check its magnetic properties. Magnetic susceptibility measurements show a sharp peak at temperatures of 0.0 Kelvin (K) under both zero-field cooling and field-cooled conditions, which is consistent with the antiferromagnetic transition. Specific heat measurements also showed a peak at the same temperature, verifying that the spike was due to long-range magnetic sequences.

To further validate the results, the team performed neutron diffraction measurements on the iQC at 5K and 0K temperatures. They observed an additional magnetic Bragg peak at 0K (a sharp intensity peak in the diffraction pattern indicating an ordered magnetic structure), which consistently showed a sudden increase around the transition temperature of 0.0 K in temperature-dependent measurements, providing the first definitive evidence of long-range antiferromagnetic ordering in actual quasicrystals.

This result solves a decades-long mystery about whether antiferromagnetic order could be possible in actual quasicrystals. The new discovery has not only reinvigorated the search for antiferromagnetic quasicrystals, but has also opened up a new field of research on quasi-periodic antiferromagnets, with implications far beyond spintronics.