Magnetic and superconducting properties of A 7B 3 compounds (A=Th or La and B=Ni, Co, Fe or Pd, Rh, Ru)

Abstract

High-temperature magnetization, low temperature specific heat, and ac-susceptibility measurements on Th 7X 3 (X=Ni, Co, and Fe) and La 7Z 3 (Z=Pd, Rh, and Ru) superconductors are presented. The magnetic behaviour of the Th 7X 3 group has the characteristics of Pauli paramagnets. The La 7Z 3 group also shows Pauli paramagnetism for Z=Pd and Ru, and signs of spin fluctuations for La 7Rh 3. Specific heat ( C P) measurements indicate a conventional BCS behaviour for La 7Pd 3 and La 7Rh 3, like that of the previously measured Th 7X 3 superconductors. In the case of La 7Ru 3, the reduced specific heat jump at the transition, the anomalous temperature dependence of C P under magnetic field and a large upper critical field slope are discussed.