Magnetic frustration and short-range ordering in cubic defect spinel MgMnO3.

Magnetic properties of bulk MgMnO3, a cubic defect spinel with the structure 4MgMnO3=3[Mg2+][Mg+2 1/3Mn4+ 4/3□1/3]O4, are reported. For T > 150 K, magnetization M vs T data fits the Curie-Weiss law with μ ≃ 4μB expected for Mn4+ and θ ≃ -40 K indicating antiferromagnetic Mn4+-Mn4+coupling. For T < 150 K, a blocking temperature TB ≃ 15 K is observed below which coercivity increases with decreasing T. The electron magnetic resonance spectra yield a single broad line with g ≃ 1.9 whose linewidth increases with decreasing T leading to a peak at TB. As predicted in spinels with magnetic ions only on the B-sites, these observations suggest a magnetically frustrated state with short-range order only. [ABSTRACT FROM AUTHOR]