Electron-spin resonance of a localized moment in the superconducting state: B Ru2:Gd (B=La, Ce, Th)

The electron-spin-resonance spectrum of Gd in the type-II cubic superconductors LaRu2, CeRu2, and ThRu2 has been observed in both the normal and superconducting regimes. Upon transition from the normal to the superconducting state, the spectra exhibit (a) a change in line shape (AB ratio), (b) an increase in thermal broadening immediately below Tc(H), and (c) a change in g value. Comparison with experiments performed by others, as well as a preliminary interpretation of the data, is presented.