Synthesis and Characterization of Magnetoelectric Ba₇Mn₄O₁₅

We present the synthesis of a novel binary metal oxide material: Ba₇Mn₄O₁₅. The crystal structure has been investigated by high-resolution powder synchrotron X-ray diffraction in the temperature range of 100-300 K as well as by powder neutron diffraction at 10 and 80 K. This material represents an isostructural barium-substituted analogue of the layered material Sr₇Mn₄O₁₅ that forms its own structural class. However, we find that Ba₇Mn₄O₁₅ adopts a distinct magnetic ordering, resulting in a magnetoelectric ground state below 50 K. The likely magnetoelectric coupling mechanisms have been inferred from performing a careful symmetry-adapted refinement against the powder neutron diffraction experiments, as well as by making a comparison with the nonmagnetoelectric ground state of Sr₇Mn₄O₁₅.