^{57}Fe NMR spectra were measured on thin films of yttrium iron garnet with divalent (Ca^{2+}) and tetravalent (Ge^{4+}) cation substitutions using the spin echo technique at 4.2 K. A series of Y_{3-x}Ca_{x}Fe_{5-x}Ge_{x}O_{12} samples with 0 ≤ x ≤ 0.0 5 was prepared by an epitaxial growth from BaO/B_{2}O_{3}/BaF_{2} flux on gadolinium gallium garnet substrate. Satellite lines corresponding to the iron ions having the Ge^{4+} and Ca^{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^{4+} substituent were obtained from the experimental data. The results were compared with those previously reported for trivalent substitution (Ga^{3+}).
Series of lutetium doped yttrium iron garnet films is studied by means of ^{57}Fe nuclear magnetic resonance. Satellite spectral lines are resolved and identified in the spectra and concentrations of lutetium in dodecahedral sites as well as yttrium/lutetium antisite defects in octahedral sites are estimated. Compared to yttrium, lutetium cations are found to have stronger disposition towards creating the antisite defects.
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