Seebeck effect in the crystalline samples of EuxYb1−xB6 (x = 0, 0.082, 0.127, 0.9, 1) was investigated at temperatures 2–300 K. For all the compounds thermopower is shown to be well described by the sum of diffusion (Sd = AT) and phonon drag components. The latter contribution is induced by quasilocal (Einstein) modes of ytterbium and europium ions with characteristic temperatures ΘE(YbB6) ≈ 91 K and ΘE(EuB6) ≈ 122 K. The estimation of effective mass m* of the charge carriers proves that increasing of Eu content induces crossover from ‘heavy’ holes with mh*(x ⩽ 0.127) ≈ 0.3–0.36 m0 to ‘light’ electrons with me*(x ⩾ 0.9) ≈ 0.12–0.13 m0 (m0−free electron mass). For the Eu-rich compounds we propose the existence of additional point on the phase diagram, which corresponds to short-range magnetic order with enhanced spin fluctuations preceding the stabilization of magnetic polarons.
Read full abstract