On evaluation of Kondo-like electron transport characteristics of TLS-Kondo ferromagnets; uranium pnictochalcogenides

Abstract

The tetragonal compound UAs 1− x Se 1+ x shows two-level-system (TLS) Kondo effect in ferromagnetic state (Curie temperature T C∼100–120 K). We have examined its ab-plane electrical resistivity dependence on temperature (down to 30 mK), on magnetic field (up to 14 T) and on external pressure (up to 19.3 kbar). Observed saturation of the TLS-Kondo resistivity ρ K( T)∼1− AT n below the Kondo temperature, T K can be characterised by gradual decrease of n from the Fermi liquid value n=2 just below T K to n=1 in the range ∼3.5–7 K and to n=1/2 for over one decade of temperature below ∼3.5 K. The coefficient A from the n=1 range is scaled with T K increasing from 33 to 49 K, when T C( x) varies from 101.9 (0.048) to 108.5 K (0.029). Either longitudinal or transverse magnetoresistance is positive and low (<0.2%/T) at 0.1 K. The pressure enhances T C (=110.8 K) by 0.23 K/kbar and lowers ρ K(0)/ ρ K(300) ratio by −0.0054 kbar −1. A consistency of the evaluated characteristics with the TLS-Kondo model is discussed.