M. Della Mea

An unusual interplay among disorder, Kondo-effect and spin-glass behavior in the Kondo lattices, Ce2Au1−xCoxSi3

Abstract We report the results of magnetic measurements for the solid solution Ce2Au1−xCoxSi3. The results reveal that this solid solution is characterized by a magnetic phase diagram (plot of magnetic transition temperature versus x) unusual for Kondo lattices. In particular, the spin-glass freezing induced by disorder is observed only for the compositions at the weak coupling limit; as one approaches the quantum critical point by a gradual replacement of Au by Co, this disorder effect is surprisingly suppressed in favor of long range antiferromagnetic ordering in contrast to expectations. This unusual interplay between disorder, spin-glass freezing and the Kondo-effect calls for further refinement of theories on competition between magnetism and the Kondo effect.

Magnetic behaviour of PrFe4Sb12 and NdFe4Sb12 skutterudites

Abstract Skutterudites Pr0.73Fe4Sb12 and Nd0.72Fe4Sb12 order magnetically below 5 and 16.5 K , respectively. Pr0.73Fe4Sb12 exhibits an unusual high electronic contribution to the specific heat Cp/T of about 1000 mJ / mol K 2 ; moreover, magnetic fields of the order of 3 T are able to suppress long range magnetic order and at some critical field Cp/T behaves proportional to − ln T . Additionally, the low temperature resistivity changes from a T2 behaviour at μ 0 H=0 T to an almost linear dependence for μ0H≈3– 4 T .

Itinerant electron metamagnetism in LaCo 9 Si 4

The strongly exchange enhanced Pauli paramagnet LaCo 9 Si 4 is found to exhibit an itinerant metamagnetic phase transition with indications for metamagnetic quantum criticality. Our investigation comprises magnetic, specific heat, and nuclear magnetic resonance measurements as well as ab initio electronic structure calculations. The critical field is about 3.5 T for H∥c and 6 T for H⊥c, which is the lowest value ever found for rare earth intermetallic compounds. In the ferromagnetic state there appears a moment of about 0.2 μ B /Co at the 16k Co-sites, but significantly smaller moments at the 4d and 16l Co-sites.

Evolution of ground state properties of YbCu5−xAux

Abstract A substitution of Cu by Au in cubic YbCu5 yields YbCu4Au crystallizing in the fully ordered ternary MgCu4Sn structure, isostructural to YbCu5. The exchange of Cu by Au drives the system from a high TK to a low TK Kondo scenario, enabling long-range magnetic order to occur. Thereby, a critical concentration range is passed with the possibility of non-Fermi-liquid behavior.

A pressure and magnetotransport study of binary quasicrystal YbCd5.7

We have probed the quasicrystalline state in binary YbCd5.7 by monitoring its electrical resistivity between 1.5 and 300 K in externally applied hydrostatic pressure up to 16 kbar and measuring its magnetoresistivity up to 12 T from 0.5 to 20 K. The thermal variation of the resistivity is practically unaffected by pressure, indicating the stability of the quasicrystalline state in this pressure regime. A positive magnetoresistance, Δρ/ρ, of is observed at 0.65 K, which reduces to at 20 K in the maximum applied field of 12 T. Though the magnetoresistance of the sample investigated is about an order of magnitude larger than expected on the basis of the empirically derived relationship observed for a large number of quasicrystals, it is much below the unusually large anomalous magnetoresistance (20–200%) reported earlier in the literature. We believe that the intrinsic magnetoresistivity of YbCd5.7 in different samples may be primarily masked by the presence of traces of free Cd which is known to have a giant magnetoresistivity at low temperatures.