Researchers at Tokyo University of Science (TUS) have achieved a first in materials science: the successful synthesis of bulk, annealable ferromagnetic icosahedral quasicrystals without relying on the previously required process of rapid quenching. These newly created quasicrystals, possessing a distinctive ten-fold symmetry unlike traditional materials, open a pathway to systematically study quasiperiodic magnetism and magnetic criticality. Until now, ferromagnetic quasicrystals were unstable due to their production method, transforming into different phases upon annealing; the TUS team bypassed this limitation, creating samples with enhanced thermal stability. “Using compositionally tuned multicomponent alloying and guided by a machine-learning-based phase classifier, we developed ferromagnetic icosahedral quasicrystals with improved structural quality,” explains Professor Ryuji Tamura, leading the research alongside Dr. Farid Labib. This breakthrough establishes quasicrystals as a third platform for magnetism, alongside periodic crystals and amorphous materials.
Machine-Learning Guided Alloy Design for Ferromagnetic Quasicrystals
Professor Ryuji Tamura and Dr. Farid Labib from the Research Institute of Science and Technology at Tokyo University of Science (TUS), Japan, spearheaded the effort, achieving a breakthrough in materials design and stability. Previously, creating these materials necessitated rapid quenching, yielding unstable samples unsuitable for detailed analysis of their intrinsic magnetic characteristics. To circumvent this limitation, the TUS team first employed a machine-learning-based phase classifier, leveraging existing databases like HYPOD-X to predict promising compositions. Tamura’s initial screening generated 675 quinary alloy systems, ultimately focusing on gold-copper-aluminum-indium-R (Au-Cu-Al-In-R) combinations, where R represented gadolinium, terbium, or dysprosium. Subsequent arc melting and controlled annealing yielded three bulk ferromagnetic icosahedral quasicrystals, Au-Cu-Al-In-Gd, Au-Cu-Al-In-Tb, and Au-Cu-Al-In-Dy, demonstrating remarkable thermal stability during prolonged annealing at 723 Kelvin. X-ray diffraction confirmed a significant improvement in quasiperiodic order compared to rapidly quenched samples.
Magnetic assessments revealed long-range ferromagnetic order within a temperature range of 9.7 to 28.3 Kelvin, dependent on the R element utilized, confirming intrinsic ferromagnetic behavior. The team observed that the resulting materials exhibited distinct magnetic critical behaviors, influenced by the spin symmetry of the rare-earth element, and attributed this to differing spin fluctuations within the gadolinium system.
Magnetic and specific heat assessments demonstrated clear bulk long-range ferromagnetic order within a temperature range of 9.7 ̶ 28.3 Kelvin, depending on the constituent R element (i.e., Gd, Tb, and Dy), providing clear evidence of intrinsic ferromagnetic order in these newly discovered QCs.
The pursuit of stable quasicrystals has historically been hampered by synthetic limitations; until recently, creating these materials demanded rapid quenching, a process yielding unstable structures unsuitable for detailed analysis. This achievement marks a significant step forward, allowing for more comprehensive investigation of the intrinsic magnetic properties of these unique materials. Their initial screening of 675 quinary alloy systems pinpointed gold-copper-aluminum-indium-R (Au-Cu-Al-In-R) systems, with R representing gadolinium, terbium, or dysprosium, as particularly favorable candidates. Crucially, long-time annealing at 723 Kelvin demonstrated the thermal stability of these newly synthesized quasicrystals, a characteristic absent in previously produced samples. Subsequent X-ray diffraction studies confirmed a marked improvement in quasiperiodic order. Magnetic behavior was observed between 9.7 to 28.3 Kelvin, dependent on the R element utilized, providing definitive evidence of intrinsic ferromagnetism. Interestingly, variations in the constituent R element led to distinct magnetic critical behaviors, highlighting the interplay between quasiperiodic order and spin symmetry, and suggesting that “magnetic criticality in quasicrystals is determined by the combination of quasiperiodic order and spin symmetry,” according to Professor Tamura.
These results indicate that magnetic criticality in QCs is determined by the combination of quasiperiodic order and spin symmetry.
Farid Labib spearheaded the effort, which promises to unlock deeper understanding of magnetism in these unique materials. Previously, the necessity of rapid quenching resulted in unstable quasicrystals, hindering detailed investigations of their intrinsic magnetic properties; annealing would typically cause a transformation into more conventional, periodic crystal structures. The TUS team employed a machine-learning-based approach to identify promising alloy compositions. Magnetic behavior was observed between 9.7 to 28.3 Kelvin, varying with the R element used. Notably, the team observed distinct magnetic critical behaviors between the Gd, Tb, and Dy-based compounds, attributing the differences to variations in spin fluctuations and magnetic anisotropy.
Using compositionally tuned multicomponent alloying and guided by a machine-learning-based phase classifier, we developed ferromagnetic icosahedral QCs with unprecedented structural quality, enabling the first systematic investigations of intrinsic magnetic properties, including critical behavior, in QCs.
The creation of stable, bulk ferromagnetic quasicrystals, materials exhibiting order without traditional crystalline repetition, promises advancements in sensing, energy conversion, and information processing technologies. This breakthrough allows for systematic investigation of the intrinsic magnetic properties previously obscured by material instability. The TUS team, led by Professor Ryuji Tamura and Dr. Farid Labib, leveraged machine learning to identify promising alloy compositions. Magnetic behavior was observed between 9.7 and 28.3 Kelvin, depending on the R element. Notably, the three compounds exhibited distinct magnetic critical behaviors despite sharing the same quasiperiodic lattice. Tb- and Dy-based quasicrystals displayed characteristics of mean-field ferromagnetism, while Gd-based samples deviated toward shorter-range interactions. The team attributes this difference to stronger spin fluctuations in the Gd system, highlighting the influence of spin symmetry.
Specifically, Tb- and Dy-based icosahedral QCs showed critical parameters close to mean-field values, indicating mean-field-like ferromagnetism characterized by infinitely long-range interactions.
