Intermediate-valence icosahedral Au-Al-Yb quasicrystal

Watanuki, Tetsu; Kashimoto, Shiro*; Kawana, Daichi*; Yamazaki, Teruo*; Machida, Akihiko; Tanaka, Yukinori*; Sato, Taku*

A quasiperiodic, intermediate-valence (IV) system is realized in an icosahedral Au-Al-Yb quasicrystal. X-ray absorption spectroscopy near the Yb -edge indicates that quasiperiodically arranged Yb ions assume a mean valence of 2.61, between a divalent state (4, = 0) and a trivalent one (4, = 7/2). Magnetization measurements demonstrate that the 4 holes in this quasicrystal have a localized character. The magnetic susceptibility shows a Curie-Weiss behavior above 100 K with an effective magnetic moment of 3.81 per Yb. Moreover, a crystalline approximant to this quasicrystal is an IV compound. We propose a heterogeneous IV model for the quasicrystal, whereas the crystalline approximant is most likely a homogeneous IV system. At temperatures below 10 K, specific heat and magnetization measurements reveal non-Fermi-liquid behavior in both the quasicrystal and its crystalline approximant without either doping, pressure, or field tuning.