A non-magnetic Kondo effect in UAsSe ferromagnet?

Abstract

The upturn in the resistivity upon cooling far below the ferromagnetic transition in the metallic system UAsSe is rather unusual. Measurements on several single crystals show that its magnitude monotonically increases with decreasing Curie temperature (T_C between 101.5 and 117 K). On the other hand, the resistivity in the paramagnetic state shows a weak sample dependence only. Distinct differences for both the Sommerfeld coefficient, γ (20–40 mJ mol−1 K−2), and the Debye temperature, Θ_D (252–310 K), have been observed for crystals with different T_C values. Θ_D increases only for specimens with $\text{T}{}_{\mathrm{<mtext>C</mtext>}}\text{>111}\text{K}$, while γ=γ(T_C) shows a minimum close to $\text{T}{}_{\mathrm{<mtext>C</mtext>}}\text{=111}\text{K}$. No effect in magnetic fields up to 14 T has been observed. The observations suggest a non-magnetic Kondo effect arising from two-level systems.