ESR in Gd-doped La3/sub -//subx/V/subx/S4. A study of localized-moment--conduction-electron interactions

It is argued that the system La3/sub -//subx/V/subx/S4:Gd3+ is very suitable for studying effects arising from localized-moment--conduction-electron (d-f) interactions in a systematic way. The concentration of conduction electrons can be varied without affecting any other important parameters. Linewidths and g shifts, when performing ESR on the Gd3+ impurities (0.09 at.%) have been studied as a function of temperature and conduction-electron concentration n, using polycrystalline samples. From the linewidth measurements it is shown that temperature-dependent broadenings, observed for Gd3+ in the conducting materials, must be due to the d-f exchange interactions. By comparing the results for different concentrations n, it is shown that the free-electron model is a good one is inthese materials. Using the free-electron model, the d-f exchange integral has been estimated from the linewidth measurements. (/subF/)1/2 = 0.10 +- 0.01 eV, and from the g-shift measurement, J (0) = 0.11 +- 0.01 eV. J is proved to be independent of the conduction-electron wave vector q for a reasonable variation of q. In addition to a temperature-independent g-shift contribution, a contribution proportional to 1/T has also been measured. This shift contribution is discussed qualitatively