Reduced Manganese Moment in Manganese Chromite

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Abstract
The net magnetization, magnetic susceptibility, 55Mn nuclear magnetic resonance, and neutron‐diffraction properties of MnCr2O4 have been reinvestigated. Our results are in general agreement with earlier findings. The neutron‐diffraction pattern of MnCr2O4 evidences appreciable deviation from a pure spiral configuration. Furthermore, the susceptibility data indicate that the Mn+ + ions possess a reduced magnetic moment of about 4.3μB, rather than the previously assumed value of 5.0μB. Given the hypothesis of an admixture of quartet states with quenched orbital momentum into the 6S free‐ion ground state, the reduced value of the 55Mn hyperfine field observed in manganese chromite is consistent with this low value for the manganese moment. The interpretation of the NMR result in terms of a ferrimagnetic spiral ground‐state spin configuration remains essentially unchanged, a manganese cone angle of about 61° being indicated. The use of 4.3μB for the Mn+ + moment improves the agreement between the theoretical and observed neutron‐diffraction patterns, but the best fit is still obtained with a much smaller value for this cone angle, namely 33°. Within the spiral model, the observed magnetic‐diffraction intensities are incompatible with the larger cone angle; the NMR findings are incompatible with the smaller. Other discrepancies are also discussed.

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