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Magnetism of Tsai-type 1/1 approximants has been extensively investigated for the last decade. The experimental results on Tsai-type approximants are reviewed and the magnetic behaviors are classified and discussed in terms of the average electron-per-atom (e/a) ratio. The paramagnetic Curie-Weiss temperature # p is found to oscillate in a universal manner as a function of the e/a ratio, and the magnetic order systematically changes with the variation in # p . In addition, recent work shows that the 2/1 approximants also follow the trend observed for the 1/1 approximants, which implies that the magnetic phase diagram of the 1/1 approximants can be applicable to higher-order approximants including quasicrystals that are yet to be discovered.

Quasicrystals (QCs), first discovered in 1984, generally do not exhibit long-range magnetic order. Here, we report on long-range magnetic order in the real icosahedral quasicrystals (i QCs) Au–Ga–Gd and Au–Ga–Tb. The Au65Ga20Gd15 i QC exhibits a ferromagnetic transition at T C = 23 K, manifested as a sharp anomaly in both magnetic susceptibility and specific heat measurements, along with an appearance of magnetic Bragg peak below T C. This is the first observation of long-range magnetic order in a real quasicrystal, in contrast to the spin-glass-like behaviors observed for the other magnetic quasicrystals found to date. Moreover, when Gd is replaced by Tb, i.e., for the Au65Ga20Tb15 i QC, a ferromagnetic behavior is still retained with T C = 16 K. Although the sharp anomaly in the specific heat observed for the Au65Ga20Gd15 i QC becomes broadened upon Tb substitution, neutron diffraction experiments clearly show marked development of magnetic Bragg peaks just below T C, indicating long-range magnetic order for the Au65Ga20Tb15 i QC also. Our findings can contribute to the further investigation of exotic magnetic orders formed on real quasiperiodic lattices with unprecedented highest global symmetry, i.e., icosahedral symmetry.