Abstract
The structure and magnetic properties of LiMn2-XMgXO4 (X < 0.5) compounds prepared by the sol-gel technique were studied by means of powder X-ray diffraction and magnetic measurement. Specimens with X < 0.2 had a cubic symmetry of Fd3m, while those with X > 0.3 exhibited extra reflections attributable to the P4332 space group, where Mg2+ and Mn4+ have 1:3 cation ordering on a 16d octahedral sublattice. Mg2+-substitution led to the enhancement of low-temperature magnetic susceptibility, indicating magnetic phase conversion from antiferromagnetic to ferromagnetic characters. This was attributed to variation of the average Mn valence state. The Mn valence state was sensitive not only to the substitution but also the preparation conditions. Ideally, ferromagnetic ordering was expected in specimens of the compound with X = 0.5. However, both the magnetization and the Curie temperature depended on the preparation temperature (Tprep): they took maximum values (Ms = 4.68μB, Tc = 23K) at Tprep = 700°C, where the chemical composition of the specimen was the closest to the stoichiometric composition. The magnetic properties of Li-Mn-Mg spinel oxides were briefly discussed in comparison with those of Li-Mn-Ni spinel oxides.
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