Physical properties of the type-I clathrate phase Ba8−xEuxAuySi46−y

The effect of the substitution of rare-earth atoms for guest atoms on the low-temperature transport and magnetic properties is investigated for single-crystalline type-I clathrates with the nominal composition Ba8−xEuxAuySi46−y (x = 1.0, 1.68 and y = 4.77, 5.32). The Seebeck coefficient and Hall coefficient data show that a transition from n- to p-type conduction takes place with increasing Au content. The n-type sample presents a large maximum in the thermal conductivity due to the freezing of three phonon Umklapp scattering processes at low temperatures, whereas the maximum of thermal conductivity in the p-type sample is strongly reduced due to dominant phonon-electron scattering process. Both samples are metal-like and ferromagnetic, with Curie temperatures TC of 3.1 K and 10.0 K for x = 1.0 and 1.68, respectively. The magnetization measurement confirmed the Eu2+ state in both samples and the Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction model explains the FM-type of order in which the nearest-neighbor (NNN) and the next-nearest-neighbor (NN) interactions play a major role at x = 1.0 and 1.68, respectively.

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