Nuclear Magnetic Resonance of Mn⁵⁵ in Manganese Ferrite

Abstract

The nuclear magnetic resonance (NMR) of Mn⁵⁵ in ferrimagnetic manganese ferrite (MnFe₂O₄) was studied by using a pulsed NMR method. A pulsed NMR apparatus operating in the UHF range was constructed, as described in detail. The signal was observed in the temperature range from 90°K to 450°K and in the external field up to 14000 Oe. The observed temperature dependence of the resonance frequency was proportional to T^3⁄2 in the lower temperature range and the resonance frequency extrapolated to 0°K was 594Mc/sec, corresponding to the value of 563 KOe of hyperfine field. The nuclei involed have been identified as associated with Mn²⁺ ions located on the tetrahedral site in the spinel lattice from the external field dependence of resonance frequency. In the frequency range between 450 and 620 Mc/sec, other signals (e. g. those associated with Mn²⁺ or Mn³⁺ on the octahedral site) were not observed at room temperature. The dynamical characters of the spin echo signal (enhacement and relaxation) were also studied.