Abstract
A superconducting transition temperature of 8.0 K is reported for the nonmagnetic () C compound with the C-type structure and a derived coherence length ξ(0) of 230 Å and a penetration depth λ(0) of 860 Å. No transition down to 2 K was observed for the magnetic, mixed-valence (/ or average valence of +5.2) C compound with the same structure. Systematic variation of for the quaternary and pseudoquaternary compounds in the RC system (R=Sc, Y, La, Lu, Th, U, or magnetic lanthanides) is studied through the variation of with the R ionic radius, Ni-Ni nearest-neighbor in-plane distance, and the normal-state Pauli-like temperature-independent paramagnetic susceptibility. Maximum at 16.6 K for C with an optimum Ni-Ni distance of 2.45 Å was observed, along with a large normal-state Pauli paramagnetic susceptibility. As a comparison, the 8.0-K C superconductor has a longer Ni-Ni distance of 2.60 Å and a smaller normal-state susceptibility. Variations of the Ni(3d)-dominated conduction band and the density of states at the Fermi level N() are believed to be the driving force for the variation of nonmagnetic compounds in the present system.
- Received 12 September 1994
DOI:https://doi.org/10.1103/PhysRevB.51.420
©1995 American Physical Society