The ESR spectra of Gd in metallic single crystals of LaSb exhibit appreciable variation in the ESR line shape upon changing the temperature from 1.7 to 300 K. At low temperatures, a completely resolved fine-structure splitting appropriate to Gd in a cubic crystalline field is observed. The fourth-order cubic-crystalline-field parameter is b4 --+ 32+ 2 Oe. The increase of the temperature leads to significant narrowing effects with the result of a single anisotropic line at room temperature. A Korringa relaxation rate of AH K/T = 0,19 + 0.03 Oe/K was extracted from the thermal broadening of the collaosed spectrum. The thermal broadening of the -1/2~+1/2 fine-structure transition is considerably enhanced, however, with respect to this Korringa thermal broadening. All these features are in complete agreement with the predictions of the theory for exchange narrowing of the fine structure in metals. The ESR line shape was calculated using this theory. Comparison of the theoretical line shape with the one observed experimentally indicates the presence of an additional narrowing mechanism, This narrowing is due to Gd spin-spin interaction in LaSb. The line shape analysis yields an exchange-interaction parameter of 0.03 eV between the spin of Gd and that of the conduction electron. The same value for the exchange parameter is derived, independently, from the experimental Korringa thermal broadening.

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Linewidth measurements are reported of the ESR spectra of metallic Gd,Lal PIBE compounds (z = 1.0 to 0.01). This system is remarkable because contributions from the exchange narrowed linewidth 4 H e x and the homogeneous linewidth AHhom can be estimated. The interpretation of 4 H e x leads to values for the "exchange fields" H e as a function of the Gd concentration.Es wird uber Messungen der Linienbreiten im ESR-Spektrum metallivcher Gd,Lal-,BE-Verbindungen (z = 1.0 bis 0,Ol) berichtet. Dieses System ist insofern bemerkenswert, als die Beitrage der austauschverschmalerten Linienbreite AHex und der homogenen Linienbreite b f f h o m abgeschatzt werden konnen. Die Interpretation von AH,, fiihrt zu den Werten fur das .,Austauschfeld" H e als Funktion der Gd-Konzentration.

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The activation energy of the hopping frequency of the vanadium-3dl-electron is derived from the temperature dependence of the ESR linewidth in the following semiconducting, pentavalent vanadium-compounds: NaxV20 s, LixV205 (x<0.02), V20 s weakly doped with WO 3 or MoO 3 (Ea~0.07 eV). In V2MoOs, vanadium-3d 1-electrons are responsible for the electronic conductivity, too.