Electron-Spin Resonance And Superconductivity In Gdxla1-Xal2 Intermetallic Compounds

Electron-spin-resonance measurements of Gd in La${\mathrm{Al}}_{2}$ exhibit appreciable change of the $g$ value and linewidth upon alloying with other nonmagnetic impurities. This indicates the existence of a effect---the relaxation rate for the conduction electrons to the Gd ions ${\ensuremath{\delta}}_{\mathrm{ei}}$ exceeds that to the lattice ${\ensuremath{\delta}}_{\mathrm{eL}}$. We are able to shift the $g$ value from $g=1.988\ifmmode\pm\else\textpm\fi{}0.003$ to $g=2.11\ifmmode\pm\else\textpm\fi{}0.01$, opening the bottleneck completely. The intermetallic compounds $\mathrm{Gd}{\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Al}}_{2}$ are Abrikosov-Gorkov superconductors in the dilute limit. Measurements of the transition temperature and the upper critical field depend upon ${\ensuremath{\delta}}_{\mathrm{ei}}$ directly and ${\ensuremath{\delta}}_{\mathrm{eL}}$ indirectly. We are thus able to obtain parameters which determine superconducting critical-field and temperature behavior from magnetic resonance experiments.