Contributions to the hyperfine field at the 57 Fe nucleus in crystals with garnet structure

ENDOR measurements are performed on a number of Fe 3+ doped crystals with garnet structure (YAIG, LuAlG, TmAlG, YGaG, LuGaG, TmGaG, and EuGaG) which enabled to determine the hyperfine field at the 57 Fe nucleus. The Fe 3+ ions occupy cation sites ((a)‐sites) which are surrounded by oxygen octahedra. It is found that the hyperfine field is linear dependent on the trigonal part of the crystal field at the (a)‐site, and thus on the field gradient V zz . This dependence is attributed to the dipole‐dipole interaction between electron and nuclear spins which in higher order contributes to the hyperfine field.