Magnetic and Thermoelectric Properties of a Heterogeneous Mixed-Valence System, Yb_2Pt_3Sn_5 (Condensed Matter: Electronic Structure, Electrical, Magnetic and Optical Properties)

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We have studied the valence states and thermoelectric properties of Yb_2T_3Sn_5 (T = Pt and Pd) with two inequivalent Yb sites. For Yb_2Pt_3Sn_5, the 4f-hole occupation number n_f is estimated to be 0.4 at 300 K from the magnetic susceptibility and L_<III>-edge absorption spectrum. Intermediate-valence behaviors manifest themselves in a largely negative value of the paramagnetic Curie temperature, -216 K, a broad peak at 300 K in the magnetic part of the resistivity, and a large minimum in the thermopower, -38μV/K at 60 K. The specific heat shows no transition down to 0.6 K. These results are explained by a model in which Yb ions in one site are divalent and those in the other site are in a valence fluctuating state with a Kondo temperature of 200 K. Thus, Yb_2Pt_3Sn_5 is a rare example of the heterogeneous mixed-valence system. An isostructural compound Yb_2Pd_3Sn_5 has a larger unit-cell volume by 2.4%, which allows the Yb ions in both the sites to be divalent.
社団法人日本物理学会の論文
2003-07-15