Spin state of Mn3O4 investigated by 55Mn nuclear magnetic resonance

The Mn-55 nuclear magnetic resonance spectrum for the spinel oxide Mn3O4 was measured at low temperature to investigate the spin structure in the ground state. The spectrum consists of three peaks in the frequency range of 250-265 MHz, which corresponds to the hyperfine field range of 24-25 T. The temperature dependence of the spectrum and the rf enhancement factor show that Mn3+ ions have two different magnetic moments, one of which is strongly related to the commensurate-incommensurate phase transition. This is consistent with the picture of two magnetic moments R and S claimed from the results of a neutron experiment. Comparison with a heat-treated sample suggests a relation between the two different magnetic moments and the occupation sites of manganese ions, the tetrahedral and octahedral sites. Theoretical estimations of the dipolar hyperfine field and the observed peak splitting predict that the magnetic moments of R and S differ by 5% at maximum. The spin-spin relaxation time has a frequency dependence that induces spectrum broadening and further splitting of the peak coming from S, indicating that the Suhl-Nakamura interaction is the major relaxation mechanism in Mn3O4.