57Fe NMR study of manganese ferrites

Magnetic properties of the manganese ferrites Mnx Fe3 - x O4 are markedly influenced by the valence states of Mn and Fe ions and by their distribution between the octahedral and tetrahedral sublattices. Hyperfine methods are capable of providing useful information on these characteristics, which is difficult to obtain otherwise. In the present contribution the Mnx Fe3 - x O4 (0.52 <x <1.80) cubic single crystals are studied by means of 57Fe nuclear magnetic resonance (NMR) at the liquid helium temperature. High quality samples and sensitive NMR equipment allowed to detect several well resolved 57Fe NMR spectral lines in the frequency range of 67-74 MHz in zero external magnetic field. In order to find out the location of iron nuclei from which the lines originate we applied external magnetic fields up to 1 T. This approach allows assignment of two spectral lines to iron nuclei in octahedral sublattice and one spectral line to irons in tetrahedral sublattice