Charge transport and magnetism in Tm0:03Yb0:97B12

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 δ ≈ 4:7 meV being close to the half of the spin fluctuation energy in YbB12. Large diffusive thermopower S = AT, A = -29:1 μV/K2 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 mß ≈ 250m0 (m0 - free electron mass). The effective parameters of magnetic centers and the analysis of anomalies favor the nonequivalent states of substitute Tm ions.