Localized Electron Magnetism in the Icosahedral Au-Al-Tm Quasicrystal and Crystalline Approximant

We report the magnetic, thermal, and transport properties of the Au-Al-Tm quasicrystal, which is isostructural to the first and only quasicrystal Au-Al-Yb that shows a novel quantum critical behavior. The Tm-based quasicrystal undergoes a spin-glass-like freezing below T-f similar to 0.4 K. We also synthesize the Au-Al-Tm approximant to the quasicrystal and find that it shows a similar spin-glass-like freezing below T-f similar to 0.3 K. Both the quasicrystal and the approximant follow the Curie-Weiss law in a wide temperature range above T-f, indicating that the 4f electrons are well localized on the vertices of the icosahedron. The interspin interaction is antiferromagnetic and its magnitude is as small as similar to 1 K. The spin-glass-like freezing is presumably driven by the combined effect of the chemical disorder of Au/Al ions and the frustrated nature of the icosahedron. On the basis of these results, we discuss a possible origin of the unusual quantum criticality observed in the Yb-based system.