Ferromagnetic 2/1 Quasicrystal Approximants

The existence of various magnetic orders has recently been established in the Tsai-type 1/1 approximant Au-Al-Gd by variation of the electron-per-atom (e/a) ratio [Ishikawa et al. Phys. Rev. B 98, 220403(R) (2018)]. Here, we report ferromagnetic (FM) 2/1 quasicrystal approximants and show that the magnetic order of higher-order approximants can be tailored starting from known magnetic 1/1 approximants. The (Au,Cu)-(Al,In)-R (R = Gd, Tb) 2/1 approximants are synthesized by the simultaneous substitution of isovalent elements Cu and In for Au and Al, respectively, to the FM Au-Al-R (R = Gd, Tb) 1/1 approximants with e = 1.74. Both the (Au,Cu)-(Al,In)-R (R = Gd, Tb) 2/1 approximants exhibit a FM transition at significantly high Curie temperatures of T-C = 30.0 and 15.3 K, respectively. Therefore, this method of isovalent substitution will also enable the realization of a variety of magnetic orders for the 2/1 approximant by variation of the e/a ratio. Such isovalent substitution may also stabilize magnetic quasicrystals for a given e/a ratio, which would lead to the realization of the long-range magnetic order in quasicrystals.