Magnetic phase transition and physical properties of spinel-type nickel manganese oxide Original Research Article

A photo-induced change of the magnetism causes a great interest in the study of the perovskite-type manganese oxides, where the charge-ordered (CO) state with the ordered Mn3+ and Mn4+ alternation is broken by light illumination. We synthesized the powder samples of (Ni1−xMnx)Mn2O4 and Ni(NiyMn2−y)O4 compounds to qualify the function of the photo-induced magnetism in the spinel-type manganese oxide. Structural analysis indicates that the powder samples with excess Ni in nominal composition (y>0) clearly show the existence of NiO as the second phase. Magnetic transition without structural change was observed at 120 K in nominal NiMn2O4. The transition is associated with the spontaneous magnetic moment interpreted as a mixed ferro-ferrimagnet coming from at least three magnetic sublattices. The X-ray study shows no trace of the existence of CO state such as Mn2+ and Mn4+ or Mn3+ and Mn4+ alternation. The electron-spin resonance shows no significant change under light illumination with photon energy 1.2 eV.