ESR inGd3+-dopedLa3−xVxS4. A study of localized-moment-conduction-electron interactions. II

Abstract

Localized-moment-conduction-electron interactions are studied in the system ${\mathrm{La}}_{3\ensuremath{-}x}{V}_{x}{\mathrm{S}}_{4}:{\mathrm{Gd}}^{3+}$ ($0\ensuremath{\le}x\ensuremath{\le}\frac{1}{3}$) using the ESR technique. Measurements of linewidths and $g$ shifts as functions of temperature are reported. The investigations of a preceding paper, dealing with very dilute materials, are extended to higher concentrations of ${\mathrm{Gd}}^{3+}$ ions. The results of the preceding paper (applicability of the free-electron model, independence of the $d\ensuremath{-}f$ exchange integral of the conduction-electron wave vector) are confirmed and the absence of a bottleneck effect is shown for ${\mathrm{Gd}}^{3+}$ concentrations up to about 8 at.%. For a concentration of about 8-at.% ${\mathrm{Gd}}^{3+}$ in ${\mathrm{La}}_{2.79}{V}_{0.21}{\mathrm{S}}_{4}$, effects due to magnetic ordering show up. No evidence for magnetic ordering was found for the corresponding insulating sample. In samples containing small concentrations of magnetic impurities effects of very weak indirect exchange interactions are studied. From this considerable evidence could be obtained for the validity of the Ruderman-Kittel-Kasuya-Yosida spin-density oscillation model in ${\mathrm{La}}_{3\ensuremath{-}x}{V}_{x}{\mathrm{S}}_{4}:{\mathrm{Gd}}^{3+}$. The ESR linewidths for the insulating samples ${\mathrm{La}}_{2}$${\mathrm{S}}_{3}$: ${\mathrm{Gd}}^{3+}$ are shown to be due to purely dipolar interactions.