A New Era in Materials Science: Antiferromagnetic Quasicrystals Unveiled
Quasicrystals (QCs) are fascinating solid materials that exhibit an intriguing atomic arrangement. Unlike regular crystals, in which atomic arrangements have an ordered repeating pattern, QCs display long-range atomic order that is not periodic. Due to this ‘quasiperiodic’ nature, QCs have unconventional symmetries that are absent in conventional crystals. Since their Nobel Prize-winning discovery, condensed matter physics researchers have dedicated immense attention towards QCs, attempting to both realize their unique quasiperiodic magnetic order and their possible applications in spintronics and magnetic refrigeration.
Although theoreticians have long expected the establishment of antiferromagnetism in select QCs, it has yet to be directly observed. Experimentally, most magnetic iQCs exhibit spin-glass-like freezing behavior, with no sign of long-range magnetic order, leading researchers to question whether antiferromagnetism is even compatible with quasi periodicity – until now.
In a groundbreaking study, a research team has finally discovered antiferromagnetism in a real QC. The team was led by Ryuji Tamura from the Department of Materials Science and Technology at Tokyo University of Science (TUS), along with Takaki Abe, also from TUS, Taku J. Sato from Tohoku University, and Max Avdeev from the Australian Nuclear Science and Technology Organisation and The University of Sydney. Their study was published in the journal Nature Physics on April 11, 2025.
“As was the case for the first report of antiferromagnetism in a periodic crystal in 1949, we present the first experimental evidence of antiferromagnetism occurring in an iQC,” says Tamura. Building upon their recent discovery of ferromagnetism in the Au-Ga-R iQCs, the researchers identified a novel Tsai-type gold-indium-europium (Au-In-Eu) iQC, exhibiting 5-fold, 3-fold, and 2-fold rotational symmetries. The team conducted a series of bulk property measurements and neutron experiments to examine its magnetic nature. Magnetic susceptibility measurements showed a sharp cusp at a temperature of 6.5 Kelvin (K) for both the zero-field cooled and field-cooled conditions, consistent with an antiferromagnetic transition. Specific heat measurements also showed a peak at the same temperature, verifying that the cusp is due to a long-range magnetic order.
To further validate their results, the team performed neutron diffraction measurements of the iQC at temperatures of 10 K and 3 K. They observed additional magnetic Bragg peaks – sharp intensity peaks in the diffraction pattern indicating an ordered magnetic structure – at 3 K, which consistently showed an abrupt increase around the transition temperature of 6.5 K in temperature-dependence measurements, providing the first clear evidence of long-range antiferromagnetic order in a real QC.
As to why the Au-In-Eu iQC hosts an antiferromagnetic phase, the researchers found that, unlike previously studied iQCs, which commonly exhibit a negative Curie-Weiss temperature, this novel iQC has a positive Curie-Weiss temperature. Interestingly, they also discovered that with a slight increase in the electron-per-atom ratio through elemental substitution, the antiferromagnetic phase disappears and the iQC shows spin-glass behavior, much like previous iQCs. This suggests that iQCs with a positive Curie-Weiss temperature favor antiferromagnetic order establishment, opening new avenues for future studies to develop novel antiferromagnetic QCs by controlling the electron-per-atom ratio.
“This discovery finally resolves the longstanding issue of whether antiferromagnetic order is possible in real QCs,” adds Tamura. “Antiferromagnetic QCs could enable unprecedented functions, such as ultrasoft magnetic responses, and will bring about a revolution in spintronics and magnetic refrigeration in the future.”
The researchers’ discovery aligns with the United Nations’ sustainable development goals (SDGs) – affordable and clean energy (SDG 7), industry, innovation, and infrastructure (SDG 9) – by building energy-efficient electronics. Solving a decades-long mystery, this discovery not only reinvigorates the search for unexplored antiferromagnetic QCs but also opens a new research field of quasiperiodic antiferromagnets, with implications extending far beyond spintronics.
“Source: Tohoku University
