Nuclear magnetic resonance study of Fe3+ ions on A-sites of Fe3O4 in the low-temperature phase

The hyperfine field spectra of Fe3+ ions on A-sites have been investigated at 4.2 K by Nuclear Magnetic Resonance. From the spectra of the magnetically single domain specimin an external magnetic field, it has been confirmed that at least eight inequivalent A-sites exist. The directions of the principal and subprincipal axes of the anisotropic hyperfine field were determined for five sites, and one of the sites has mirror symmetry with reference Co the ac-plane. This cannot be explained by the symmetry groups Cc and c-glide which have been proposed by diffraction studies. For the sites with a lower hyperfine magnetic field (less than or equal to 508.5 kOe), the anisotropic part of the field is appreciably larger than the dipole field from the nearest-neighbour Fe ions on the B-sites. This result suggests a delocalization of the electron cloud of neighboring B-sites.