Magnetic-Resonance Study of Iron in Silver Chloride

The cubic electron-spin-resonance spectrum of ${\mathrm{Fe}}^{3+}$ in silver chloride has been studied at 1.3°K by the electron-nuclear-double-resonance (ENDOR) technique. ENDOR lines from 6 to 24 Mc/sec were observed on each of the five electron-spin-resonance transitions and have been identified as lines due to four chlorine nuclei which are nearest neighbors to the iron ion. The angular dependence of the crystal-field splitting of the electron resonance, as the orientation of the applied field is varied, proves that the iron is in a site of cubic symmetry. The angular variation of the ENDOR spectrum, as the field is rotated in a (100) plane, shows that the iron cannot be in a site of octahedral symmetry and that it therefore must be in a site of tetrahedral symmetry. ENDOR lines of both chlorine isotopes were identified. ${\mathrm{Cl}}^{35}$ ENDOR lines, chartetrahedral by $M_s=+\frac{3}{2}$ and $M_s=-\frac{3}{2}$, were studied with the applied field parallel to the [100] direction, and the best chlorine hyperfine and quadrupole coupling constants were determined for both isotopes. It is found that these constants can be used to predict the locations of all observed ${\mathrm{Cl}}^{35}$ and ${\mathrm{Cl}}^{37}$ ENDOR lines, but some discrepancies between the predicted spectrum and the observed lines remain which cannot be accounted for by effects of the cubic-field splitting term in the spin Hamiltonian.