Experimental Observation of Long-Range Magnetic Order in Icosahedral Quasicrystals

[Image: see text] 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 Au(65)Ga(20)Gd(15)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 Au(65)Ga(20)Tb(15)i QC, a ferromagnetic behavior is still retained with T(C) = 16 K. Although the sharp anomaly in the specific heat observed for the Au(65)Ga(20)Gd(15)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 Au(65)Ga(20)Tb(15)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.