Hyperfine Field in YIG with Charged Substitution

$\text{}^{57}$Fe NMR spectra were measured on thin films of yttrium iron garnet with divalent (Ca$\text{}^{2+}$) and tetravalent (Ge$\text{}^{4+}$) cation substitutions using the spin echo technique at 4.2 K. A series of Y$\text{}_{3-x}$Ca$\text{}_{x}$Fe$\text{}_{5-x}$Ge$\text{}_{x}$O$\text{}_{12}$ samples with 0 ≤ x ≤ 0.0 5 was prepared by an epitaxial growth from BaO/B$\text{}_{2}$O$\text{}_{3}$/BaF$\text{}_{2}$ flux on gadolinium gallium garnet substrate. Satellite lines corresponding to the iron ions having the Ge$\text{}^{4+}$ and Ca$\text{}^{2+}$ in their neighbourhood were identified. The sample with the germanium content of x(Ge) = 0.004 and (110) substrate orientation was used for a detailed study: NMR spectra of this sample were measured in an external magnetic field of 0.1 T applied along several directions in the plane of the film. The modification of the isotropic part and the anisotropy tensor of the hyperfine interaction caused by the Ge$\text{}^{4+}$ substituent were obtained from the experimental data. The results were compared with those previously reported for trivalent substitution (Ga$\text{}^{3+}$).