Umbrella Structure in Pr, Nd and Yb Substituted YIG Studied by 57Fe NMR

The NMR spectra of 57Fe in Pr :YIG, Nd : YIG and Yb :YIG were measured on polycrystalline samples at 4.2 K in the zero external field. In the NMR spectra of both tetrahedral and octahedral sites the resolved satellite structure appears. This structure is caused by the change of the hyperfine field on the nuclei of those Fe3+ ions, which are the nearest or next nearest neighbours of the substituted Re3+ ion. The change of the hyperfine field is given by the change of dipole and transferred contribution. Both contributions are sensitive to the kind of Re3+ ion and to the value and direction of its magnetic moment. The satellite structure of NMR spectra provides sufficient amount of information (splitting) to find unknown parameters of the non-collinear (umbrella) arrangement of Re3+ magnetic moments