Modification of hyperfine field on⁵⁷Fe nuclei in substituted ferrimagnetic garnets

Abstract

We review the results of the NMR on⁵⁷Fe nuclei in a number of ferrimagnetic garnets Y_3−x R_xFe₅O₁₂ (R =rare earth or Bi) and Y₃Fe_5−xM_xO₁₂ (M=Al, Ga, In). For suitable concentrations of substituted ions (x∼0.1–0.4) satellite lines in the NMR spectra of both tetrahedral and octahedral Fe ions are observed. These satellites correspond to Fe ions in the vicinity of which single substitution is situated. The splitting between the satellite and the parent line has its origin in the change of the dipolar field and in the change of crystal field effects (including the transfer of electrons). While the dipolar field is easily calculated, once the magnetic moments and the geometry is known, the origin of the change of the crystal field effects is much less clear. Experimental results show that it is anisotropic and that in some cases the anisotropy may be substantial. This anisotropy is discussed within the framework of the semiempirical “independent bond” method.