Evolution of thermoelectric properties in EuYbBfamily.

Seebeck effect in the crystalline samples of EuYbB(= 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 (=) and phonon drag components. The latter contribution is induced by quasilocal (Einstein) modes of ytterbium and europium ions with characteristic temperatures Θ(YbB) ≈ 91 K and Θ(EuB) ≈ 122 K. The estimation of effective massof the charge carriers proves that increasing of Eu content induces crossover from 'heavy' holes with(⩽ 0.127) ≈ 0.3-0.36to 'light' electrons with(⩾ 0.9) ≈ 0.12-0.13(-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.