A non-magnetic Kondo effect in UAsSe ferromagnet?

The upturn in the resistivity upon cooling far below the ferromagnetic tran sition in the metallic system UAsSe is rather unusual. Measurements on seve ral single crystals show that its magnitude monotonically increases with de creasing 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, gamma (20-4 0 mJ mol(-1) K-2), and the Debye temperature. Theta (D) (252-310K), have be en observed for crystals with different Tc values. OD increases only for sp ecimens with T-c > 111 K, while gamma = gamma (T-c) shows a minimum close t o Tc = 111 K. No effect in magnetic fields up to 14 T has been observed. Th e observations suggest a non-magnetic Kondo effect arising from two-level s ystems. (C) 2001 Elsevier Science B.V. All rights reserved.