World's First Ferromagnetic Icosahedral Quasicrystals Realized Without Ultra-Rapid Cooling - Research on Quasicrystal Magnetism Enters New Phase with High-Quality Samples

【Research Summary and Key Points】

In a five-element alloy system Au-Cu-Al-In-R (R = Gd, Tb, Dy) containing rare-earth elements, stable ferromagnetic icosahedral quasicrystals were successfully fabricated for the first time in the world using conventional arc melting and heat treatment.

The systematic differences in magnetic critical behavior depending on the type of rare-earth element (Gd, Tb, Dy) were quantitatively clarified, and it was shown that their origin lies in the combination of the quasiperiodic structure and spin symmetry.

This research demonstrates that quasicrystals are a new material platform whose magnetic critical behavior can be controlled by composition design, and it is expected to significantly advance research on magnetism and quantum phenomena in quasiperiodic structures.

【Research Overview】

A joint research group led by Professor Ryuji Tamura of the Department of Materials and Manufacturing Science, Faculty of Science and Technology, Tokyo University of Science, has succeeded for the first time in the world in fabricating ferromagnetic icosahedral quasicrystals, which were previously only obtainable by a special "ultra-rapid cooling method (*1)" involving extremely fast cooling of molten alloys, using conventional arc melting and heat treatment. Conventional ferromagnetic quasicrystals were metastable phases dependent on ultra-rapid cooling, making high-quality fabrication and precise property evaluation difficult. With this achievement, ferromagnetic quasicrystals have evolved from special metastable substances to a new class of magnetic materials that can be fabricated and high-quality processed by conventional heat treatment, opening the way for full-scale research into magnetic phase transitions and magnetic critical phenomena (*3) in quasiperiodic structures.

Quasicrystals (*4) are special materials that, while lacking periodicity in their atomic arrangement, exhibit extensive order known as long-range order, and have attracted attention for their unique electronic and thermal properties, different from those of ordinary crystals. However, the intrinsic magnetism of ferromagnetic quasicrystals has been difficult to understand because they have only been obtainable as metastable phases through ultra-rapid cooling. Therefore, this research group considered the realization of quasicrystals that do not require ultra-rapid cooling to be key to their elucidation, and explored new quasicrystal candidates using machine learning, followed by their synthesis and property evaluation.

This time, the synthesis of three new types of icosahedral quasicrystals composed of five metallic elements: Au (gold), Cu (copper), Al (aluminum), In (indium), and R (R = Gd (gadolinium), Tb (terbium), Dy (dysprosium)) was successful. These can be fabricated by conventional arc melting and heat treatment and exhibit excellent thermal stability, maintaining their quasiperiodic structure even after prolonged heat treatment. All quasicrystals showed clear ferromagnetic order, while their magnetic critical behavior systematically differed depending on the type of rare-earth element. It was quantitatively revealed that the Gd system deviates significantly from mean-field theory (*5), whereas the Tb and Dy systems exhibit mean-field-like behavior. These results indicate that the magnetic critical behavior in quasicrystals is determined by the combination of the quasiperiodic structure and spin symmetry (*6), and suggest a new material design guideline for controlling magnetic critical behavior by selecting rare-earth elements.

Furthermore, this research is an interdisciplinary study that fuses materials science, condensed matter physics, crystallography, and AI, and is significant in that new substances predicted by machine learning were actually synthesized and discovered. This achievement also opens the door to fabricating ferromagnetic quasicrystals without reliance on ultra-rapid cooling, providing a research foundation for full-scale investigation of magnetic phase transitions and quantum phenomena in quasiperiodic structures.

These research results were published online on July 7, 2026, in the international academic journal "Journal of the American Chemical Society."

【Background of the Research】

Magnetic properties in crystalline and amorphous materials have been studied for many years, and the understanding of magnetic order has greatly advanced. On the other hand, quasicrystals, with their non-periodic structure possessing five-fold rotational symmetry (pentagonal or star-like) not found in ordinary crystals, were thought to be incapable of forming long-range magnetic order, only short-range or spin-glass-like (*7) magnetic order.

However, this conventional wisdom was overturned by the discovery of ferromagnetic quasicrystals in the Au-Ga-Gd and Au-Ga-Tb systems by this research group in 2021 (Note 1). This demonstrated that spontaneous magnetization and long-range magnetic order could be realized even on a quasiperiodic lattice, and quasicrystals have come to be recognized as a "third magnetic platform" following crystals and amorphous materials. However, all ferromagnetic quasicrystals discovered to date have been metastable phases obtainable only through ultra-rapid cooling, and they transform into stable periodic crystals upon annealing. Consequently, structural improvement and precise measurements were difficult, and it was not possible to quantitatively investigate the magnetic critical phenomena unique to quasicrystals.

Therefore, this research aimed to realize ferromagnetic icosahedral quasicrystals that do not require ultra-rapid cooling, and conducted candidate material exploration using machine learning. This was a crucial task for establishing ferromagnetic quasicrystals as a new class of magnetic materials that can be produced with high quality.

Note 1: Tokyo University of Science Press Release (November 19, 2021)

"Discovery of Ferromagnetic Quasicrystals - A Leap Forward in Understanding the Unique Magnetism Exhibited by Quasiperiodicity."

【Details of Research Results】

Three types of five-element icosahedral quasicrystals (Gd system: Au54Cu7.5Al12In12Gd14.5, Dy system: Au57.5Cu5Al13In10Dy14.5, Tb system: Au57.5Cu5.5Al10.5In12Tb14.5), which were top candidates from the machine learning classifier, were synthesized. Their average valence electron number (e/a, *8) was 1.77, 1.74, and 1.75, respectively, all close to the value for Tsai-type ferromagnetic quasicrystals (e/a ≈ 1.7). The synthesized quasicrystals undergo a phase transition to an approximant crystal at temperatures above 723 K (K is Kelvin; 0°C is approximately 273.1 K), but were found to maintain stability at temperatures below 723 K even after prolonged heat treatment. Furthermore, prolonged heat treatment at 723 K resulted in sharper X-ray diffraction peaks, confirming that the disorder in atomic arrangement decreases and quasicrystalline order is formed over a wider range due to heat treatment.

The synthesized Gd, Dy, and Tb quasicrystals showed clear ferromagnetic transitions at Curie temperatures (*9) of TC = 28.3 K, 16.5 K, and 9.7 K, respectively. Specific heat measurements revealed significant lambda-type transitions (*10) at each phase transition temperature, confirming the presence of long-range ferromagnetic order. Furthermore, magnetization measurements showed that the Gd system quasicrystal exhibited isotropic Heisenberg-type (*11) behavior, saturating magnetization at low magnetic fields (approx. 0.6 T). In contrast, the Tb and Dy system quasicrystals exhibited non-Heisenberg-type behavior, with magnetization not saturating even under high magnetic fields (up to 7 T), due to strong directional dependence of spin orientation (single-ion anisotropy).

These differences in properties are thought to be due to differences in spin symmetry. In Gd3+, which lacks orbital angular momentum, isotropic spin fluctuations are large, and their influence leads to critical behavior that deviates from the predictions of mean-field theory. In contrast, in Tb3+ and Dy3+, strong magnetic anisotropy suppresses spin fluctuations, stabilizing behavior closer to mean-field theory. These results indicate that the magnetic critical behavior in quasicrystals is determined by the combination of the quasiperiodic structure and spin symmetry, and that quasiperiodicity is an important factor characterizing magnetic critical phenomena.

This research is the world's first realization of ferromagnetic quasicrystals that do not require ultra-rapid cooling, and it opens the way to studying magnetic phase transitions in quasiperiodic structures with high-quality samples.

Professor Tamura of Tokyo University of Science, who led this research, commented, "This achievement allows us to fabricate ferromagnetic quasicrystals without relying on ultra-rapid cooling, opening the path to studying magnetism and quantum phenomena arising from quasiperiodic structures with high-quality samples. We believe that ferromagnetic quasicrystals, previously considered special metastable substances, have now entered a phase where they can be studied in earnest as a new class of magnetic materials."

This research was supported by Grants-in-Aid for Scientific Research (JP19H05817, JP19H05818, JP19H05819, JP21H01044) from the Japan Society for the Promotion of Science (JSPS) and the Strategic Basic Research Programs CREST (JPMJCR22O3) from the Japan Science and Technology Agency (JST).

【Terms】

*1 Ultra-rapid cooling method

A special fabrication method involving extremely rapid cooling of molten alloys. It can form metastable phases unobtainable by conventional heat treatment, but has limitations on sample size and quality.

*2 Ferromagnetic icosahedral quasicrystal

Among quasicrystals, those with icosahedral symmetry (non-periodic symmetry with five-fold, three-fold, and two-fold rotation axes) in which ferromagnetism is realized. Ferromagnetism is a strong magnetic order where magnetic moments of adjacent atoms spontaneously align in the same direction. It was thought that regular alignment of magnetic moments would be difficult in quasicrystals due to the lack of long-range periodicity. However, the existence of ferromagnetic quasicrystals in the Au-Ga-Gd and Au-Ga-Tb systems was reported in 2021, attracting attention as a phenomenon that overturns conventional solid-state physics by coexisting non-periodic structure and long-range magnetic order.

*3 Magnetic critical phenomenon

A phenomenon where physical quantities such as magnetization and specific heat exhibit singular behavior according to power laws when a substance transitions between a magnetically ordered state and a non-ordered state at a specific temperature, such as the Curie temperature or Néel temperature.

*4 Quasicrystal

A solid structure that, despite lacking the periodic atomic arrangement of ordinary crystals, exhibits long-range order and sharp diffraction patterns, unlike amorphous materials. Its most distinctive feature is possessing symmetries forbidden in crystals, such as five-fold symmetry. It is a solid state located between crystals and amorphous materials, possessing order but not periodicity.

*5 Mean-field theory

An approximation method in which the interaction with each spin in a many-body system is replaced by the average effect (mean field) of surrounding spins, ignoring individual fluctuations.

*6 Spin symmetry

A property indicating the tendency of spins to align in a particular direction.

*7 Spin-glass-like

A special type of magnetic material in which electron spins are fixed in random orientations.

*8 Average valence electron number (e/a)

The number of valence electrons per atom. An important indicator that determines the crystal structure and magnetic properties of a substance.

*9 Curie temperature

The temperature at which a ferromagnetic material loses its magnetic order.

*10 Lambda-type transition

A continuous phase transition where the specific heat curve exhibits a peculiar shape resembling the Greek letter lambda (λ).

*11 Heisenberg-type

A magnetic model in which spins are not constrained to a specific direction and can freely change their orientation in three-dimensional space.

【Publication Information】

Journal:

Journal of the American Chemical Society

Article Title:

Bulk Ferromagnetic Icosahedral Quasicrystals without Rapid Quenching

Authors:

Ryuji Tamura, Farid Labib, Kazuki Inagaki, Ryo Takeuchi,

Takafumi Tsugawa, Takenori Fujii, Shintaro Suzuki, Asuka Ishikawa, Chang Liu, Minoru Kusaba, Ryo Yoshida

DOI:

10.1021/jacs.6c03748

【Presenters】

Ryuji Tamura

Professor, Department of Materials and Manufacturing Science, Faculty of Science and Technology, Tokyo University of Science (Corresponding Author)

Farid Labib

Assistant Professor, Research Support Center, Advanced Research Institute for Science and Engineering, Tokyo University of Science

Kazuki Inagaki

Completed Master's Program, Department of Materials and Manufacturing Science, Graduate School of Science and Technology, Tokyo University of Science, 2019

Ryo Takeuchi

Completed Master's Program, Department of Materials and Manufacturing Science, Graduate School of Science and Technology, Tokyo University of Science, 2022

Takafumi Tsugawa

Completed Master's Program, Department of Materials and Manufacturing Science, Graduate School of Science and Technology, Tokyo University of Science, 2022

Takenori Fujii

Assistant Professor, Division of Research and Development, Center for Low Temperature Science, The University of Tokyo

Shintaro Suzuki

Assistant Professor, Department of Physics, Faculty of Science and Technology, Aoyama Gakuin University

Asuka Ishikawa

Technical Staff, Research Center for Advanced Science and Technology, Graduate School of Engineering, The University of Tokyo

Chang Liu

Associate Professor, Center for Advanced Data Science, Research Organization of Information and Systems, The Institute of Statistical Mathematics; Visiting Researcher, Advanced Scientific Computing Program (AGIS), Advanced Scientific Computing Program (AGIS), RIKEN

Minoru Kusaba

Project Assistant Professor, Department of Advanced Materials Science, National Institute for Fusion Science, National Institutes of Natural Sciences

Ryo Yoshida

Professor and Center Director, Center for Advanced Data Science, Research Organization of Information and Systems, The Institute of Statistical Mathematics

【Contact Information Regarding Research】

Ryuji Tamura (tamura【@】rs.tus.ac.jp)

Professor, Department of Materials and Manufacturing Science, Faculty of Science and Technology, Tokyo University of Science

【Regarding JST Projects】

Shinji Kanayama (crest【@】jst.go.jp)

Green Innovation Group, Department of Strategic Basic Research Programs, Japan Science and Technology Agency

TEL: 03-3512-3531 FAX: 03-3222-2066

【Contact Information for Media and Public Relations】

Public Relations Section, Management Planning Department, Tokyo University of Science

TEL: 03-5228-8107 FAX: 03-3260-5823

E-mail: koho【@】admin.tus.ac.jp

Public Relations Division, Japan Science and Technology Agency

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