Synthesis and Characterization of Magnetoelectric Ba 7 Mn 4 O 15 .

We present the synthesis of a novel binary metal oxide material: Ba 7 Mn 4 O 15 . 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 Sr 7 Mn 4 O 15 that forms its own structural class. However, we find that Ba 7 Mn 4 O 15 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 Sr 7 Mn 4 O 15 .