Bulk ferromagnetic quasicrystals emerge without rapid quenching, unlocking stable magnetic studies

A groundbreaking discovery in the field of materials science has opened new avenues for studying ferromagnetism in quasicrystals. Researchers have successfully created bulk ferromagnetic quasicrystals without relying on rapid quenching, a method that had previously limited the structural integrity and stability of such materials. This achievement marks a significant shift in understanding how quasicrystals can be utilized for exploring intrinsic magnetic properties, offering a more robust foundation for future studies. The development of these quasicrystals comes after years of challenges in achieving stable structures that could support detailed investigation of their magnetic characteristics. Ferromagnetism, typically observed in both periodic crystals and amorphous materials, had proven difficult to realize in quasicrystals due to their unique long-range quasiperiodic order and unconventional rotational symmetries. However, recent advancements have allowed scientists to observe ferromagnetism in gold-based icosahedral quasicrystals, establishing them as a novel platform for magnetic research. Previously, all known ferromagnetic quasicrystals required synthesis through rapid quenching, a process that resulted in metastable and structurally flawed materials. When subjected to annealing, these quasicrystals transformed into approximant crystals, which, while similar in local atomic structure, possessed periodic order rather than the quasiperiodic nature of quasicrystals. This transformation hindered the ability to study the intrinsic magnetic properties of true quasicrystals, particularly aspects such as magnetic criticality, which describe the behavior of a material near a magnetic phase transition. To overcome these limitations, a research team led by Professor Ryuji Tamura from the Department of Materials Science and Technology and Dr. Farid Labib from the Research Institute of Science and Technology at Tokyo University of Science (TUS) in Japan employed a novel approach. They used a machine-learning-based phase classifier to guide the selection of suitable alloy compositions for creating stable ferromagnetic icosahedral quasicrystals. By analyzing data from the HYPOD-X QC database and other existing resources, they identified 675 potential quinary alloy systems. Among these, the gold-copper-aluminum-indium-rare earth (Au-Cu-Al-In-R) systems showed the greatest promise. Specifically, the combinations involving rare earth elements such as gadolinium (Gd), terbium (Tb), and dysprosium (Dy) were selected for further exploration. Using conventional arc melting techniques followed by controlled annealing, the researchers synthesized three bulk quinary ferromagnetic icosahedral quasicrystals: Au-Cu-Al-In-Gd, Au-Cu-Al-In-Tb, and Au-Cu-Al-In-Dy. These newly developed quasicrystals demonstrated remarkable stability even under prolonged annealing at high temperatures, specifically at 723 Kelvin. X-ray diffraction analyses confirmed a notable enhancement in quasiperiodic order compared to earlier ferromagnetic quasicrystals made via rapid quenching methods. Magnetic and specific heat measurements also indicated the presence of long-range ferromagnetic order within a temperature range of 9.7 to 28.3 Kelvin, depending on the rare earth element incorporated. This finding provides clear evidence of intrinsic ferromagnetic ordering in these newly discovered quasicrystals. Despite sharing the same quasiperiodic lattice structure, each compound displayed distinct magnetic critical behaviors influenced by the single-ion magnetic anisotropy of the respective rare earth elements. This variation suggests that the magnetic properties of quasicrystals can be finely tuned based on the choice of constituents, opening up possibilities for tailoring materials with specific magnetic responses for various applications. This breakthrough paves the way for further exploration of quasicrystals' magnetic properties, potentially leading to innovations in technology and materials engineering. With the newfound ability to create stable bulk quasicrystals, researchers can now conduct more comprehensive studies on their magnetic behaviors, contributing significantly to the broader understanding of magnetism in non-periodic solids. Future work will likely focus on expanding the range of elements used in these alloys and investigating the practical implications of these findings in real-world applications.