Browsing by Author "Tamura, R"

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    Experimental observation of long-range magnetic order in icosahedral quasicrystals
    (American Chemical Society, 2021-11-17) Tamura, R; Ishikawa, A; Suzuki, S; Kotajima, T; Tanaka, Y; Seki, T; Shibata, N; Yamada, T; Fujii, T; Wang, CW; Avdeev, M; Nawa, K; Okuyama, D; Sato, TJ
    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 Au65Ga20Gd15i QC exhibits a ferromagnetic transition at TC = 23 K, manifested as a sharp anomaly in both magnetic susceptibility and specific heat measurements, along with an appearance of magnetic Bragg peak below TC. 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 Au65Ga20Tb15i QC, a ferromagnetic behavior is still retained with TC = 16 K. Although the sharp anomaly in the specific heat observed for the Au65Ga20Gd15i QC becomes broadened upon Tb substitution, neutron diffraction experiments clearly show marked development of magnetic Bragg peaks just below TC, indicating long-range magnetic order for the Au65Ga20Tb15i 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. © 2021 The Authors - CC BY. Published by American Chemical Society
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    Long-range magnetic order in real icosahedral quasicrystals
    (Research Square, 2021-03-22) Tamura, R; Ishikawa, A; Suzuki, S; Kotajima, A; Tanaka, Y; Seki, T; Shibata, N; Yamada, T; Fujii, T; Wang, CW; Avdeev, M; Sato, T
    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 TC = 23 K, manifested as a sharp anomaly in both magnetic-susceptibility and specific-heat measurements. Quick magnetic saturation to almost the full moment (7μB/Gd3+) is observed under 100 Oe at 2 K. This is the first observation of long-range magnetic order in a real quasicrystal, in contrast to the spin-glass-like behaviours 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 behaviour is still retained with TC = 16 K. Although the sharp anomaly in the specific heat observed for the Au65Ga20Gd15 i QC is significantly broadened upon Tb substitution, neutron-diffraction experiments clearly show the marked development of magnetic Bragg peaks below TC, 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. © This work is licensed under a CC BY 4.0 License.
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    Magnetic properties of the quasicrystal approximant Au65Ga21Tb14
    (American Physical Society, 2023-05-31) Nawa, K; Avdeev, M; Ishikawa, A; Takakura, H; Wang, CW; Tamura, R; Okuyama, D; Satao, TJ; Murasaki, R
    The magnetic properties of the quasicrystal approximant Au65Ga21Tb14 were investigated using magnetization and neutron diffraction experiments. The temperature dependences of the magnetic susceptibility and magnetization curve indicate dominant ferromagnetic interactions, whereas a whirling antiferromagnetic order was observed in neutron diffraction experiments. In the antiferromagnetic phase, the magnetic moments are aligned almost perpendicular to a pseudofivefold symmetry axis, which corresponds to the easy-axis direction of a Tb atom. Magnetic properties similar to those of Au72Al14Tb14 in spite of the substantial difference in the Au concentration suggest the robustness of the easy-axis anisotropy against the chemical environment. ©2023 American Physical Society
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    Whirling spin order in the quasicrystal approximant Au72Al14Tb14
    (American Physical Society, 2019-08-13) Sato, TJ; Ishikawa, A; Sakurai, A; Hattori, M; Avdeev, M; Tamura, R
    A neutron powder diffraction experiment has been performed on the quasicrystal approximant Au72Al14Tb14, a body-centered-cubic crystal of icosahedral spin clusters. The long-range antiferromagnetic order was confirmed at the transition temperature TN=10.4 K. The magnetic structure consists of noncoplanar whirling spins on the icosahedral clusters, arranged in an antiferroic manner. A simple icosahedral spin-cluster model with uniaxial anisotropy accounts well the whirling spin order as well as the in-field metamagnetic transition, indicating that the icosahedral symmetry is essential. ©2019 American Physical Society