Charge Transport and Magnetism in Tm_0.03Yb_0.97B₁₂

Abstract

Transport and magnetic properties of polycrystalline Tm0.03Yb0.97B12 samples were investigated at temperatures 1.8-300 K in magnetic fields up to 9 T. The activated behavior of resistivity, the Hall coefficient and thermopower is described in terms of a narrow gap εg ≈ 16.6 meV, which controls the charge transport in Tm0.03Yb0.97B12 at T > 40 K. The maximum of magnetic susceptibility found at 50 K is shown to be induced by a spin gap ∆ ≈ 4.7 meV being close to the half of the spin fluctuation energy in YbB12. Large diffusive thermopower S = AT , A = −29.1 µV/K 2 and the Pauli susceptibility χ0 ≈ 7.2 × 10 −3 emu/mol found below 20 K seem to be associated with the many-body resonance, which corresponds to states with an enhanced effective mass m * ≈ 250m0 (m0 -free electron mass). The effective parameters of magnetic centers and the analysis of anomalies favor the nonequivalent states of substitute Tm ions.