Magnetic response of the CE structure in the doping-free system NaMn7O12

We investigated the magnetic properties of the CE structure in NaMn7O12, characterized by the absence of cation disorder and structural inhomogeneities, where an unusual 3dx2-y2 orbital order is expected. Magnetization data show two salient features: a remanent magnetization below the magnetic ordering and a susceptibility anomaly at the charge ordering. The former feature suggests the existence of uncompensated spins in the CE structure. The latter, common to a variety of manganites, is quantitatively explained as an increase of the antiferromagnetic coupling concomitant with the Jahn-Teller distortion of both Mn3+O6 and Mn4+O6 octahedra.