Analysis of the exchange magnetic structure in [Pb.sub.3][Mn.sub.7][O.sub.15]

The indirect-coupling model is used to analyze the exchange magnetic structure of [Pb.sub.3][Mn.sub.7][O.sub.15] in the hexagonal setting. The ratios of manganese ions [Mn.sup.4+]/[Mn.sup.3+] in each nonequivalent position are determined. [Pb.sub.3][([Mn.sub.0.95][Ge.sub.0.05]).sub.7][O.sub.15] and [Pb.sub.3][([Mn.sub.0.95][Ga.sub.0.05]).sub.7][O.sub.15] single crystals are grown by the solution-melt method in order to test the validity of the proposed model. The structural and magnetic properties of the single crystals are studied. The magnetic properties of the grown single crystals are compared with those of nominally pure [Pb.sub.3][Mn.sub.7][O.sub.15].