PURPOSE: To prepare the titled compound useful as a catalyst or a raw material of semiconductor, by mixing the oxides of Lu, Mn and Al at specific ratios, and heating the mixture.

CONSTITUTION: Lu2O3, MnO and Al2O3 are mixed together at molar ratios of about 1:2:1, and the mixture is heated at ≥1,300°C in a nonoxidizing atmosphere to obtain the compound represented by LuAlMnO4. YFe2O4 is a known compound having hexagonal lamellar structure and magnetism, and represented by the formula Y3+Fe2+Fe3+O42- wherein both iron ions and Y are surrounded by 5- and 6-coorindated O ions respectively. LuAlMnO4 is a novel compound having hexagonal lamellar structure of the figure obtained by replacing the Y3+, Fe2+ and Fe+3 of the above compound with Lu3+, Mn2+ and Al3+, respectively. In the figure, the large circle represents O, the small circle Tm, and the solid circle Al and Mn. The solid circles are distributed randomly, and Mn2+ and Al3+ are surrounded by 5-coordinated O ions and take the same positions in the crystallographic meaning. Lu is surrounded by 6-coordinated O, and O atoms take the close-packed configuration.