Quasicrystals are solids with quasiperiodic atomic structures and symmetries. They have long-range order, but they lack periodicity. Since their discovery, scientists have sought physical properties related to their peculiar structure.
An international group of researchers led by the Tokyo University of Science has recently discovered long-range magnetic order in quasicrystals with icosahedral symmetry that turns ferromagnetism below certain temperatures. The study is the first-ever observation of long-range ferromagnetic order in icosahedral quasicrystals (i QCs).
Ryuji Tamura of Tokyo University of Science (TUS) said, “This successful synthesis of ferromagnetic i QCs is the culmination of more than ten years of research in our laboratory. Nobody knows what kind of peculiar behavior they will further reveal or how they can be exploited to advance technology, but now we have finally taken the first step. Elucidating the properties of these ferromagnetic i QCs will contribute greatly to the development of science.”
Magnetic order has four major types: ferromagnetism, antiferromagnetism, paramagnetism, and diamagnetism. The discovery of antiferromagnetic and ferromagnetic transitions in approximant crystals (APs) inspired scientists to observe magnetically ordered i QCs.
For this study, scientists prepared alloys of gold (Au), gallium (Ga) and gadolinium (Gd), and gold, gallium, and terbium (Tb). They used conventional X-ray diffraction to observe the formation of an icosahedral quasicrystal phase for both Au-Ga-Gd and Au-Ga-Tb.
Using magnetic susceptibility and specific heat measurements, scientists then explore the properties of two i QCs. Both alloys showed a ferromagnetic phase transition at 23 K (Gd i QC) and 16 K (Tb i QC), a signature of long-range magnetic order.
They further validated their results by performing neutron diffraction experiments using ECHIDNA (ANSTO, Australia) and ISSP-GPTAS (JRR-3, Japan). They observed the neutron diffraction patterns of the i QCs at different temperatures. Later, they observed prominent Bragg peaks below their respective transition temperatures, confirming the ferromagnetic nature of the i QCs.
Tamura said, “The discovery of long-range ferromagnetic order in this study has consequences far beyond the landscape of the physical properties of materials and opens doors to tailored magnetic materials. The crystal symmetry of ferromagnetic QCs is much higher than that of conventional periodic crystals, which makes it possible to apply them as ultrasoft magnetic materials.”
- Ryuji Tamura et al., Experimental Observation of Long-Range Magnetic Order in Icosahedral Quasicrystals, Journal of the American Chemical Society (2021). DOI: 10.1021/jacs.1c09954