Molecule-like cluster magnetism and cationic order in the new hexagonal perovskite Ba 4 Sn 1.1 Mn 2.9 O 12 .

The new hexagonal perovskite phase of composition Ba 4 Sn 1.1 Mn 2.9 O 12 has been synthesized by solid-state reactions at 1673 K. The crystal structure has been investigated using X-ray and neutron diffraction. The hexagonal perovskite structure has an ordered arrangement of Sn and Mn ions on the corner-sharing octahedral centers and the face-sharing octahedral centers respectively. Short Mn-Mn distances have been evidenced in the face-sharing trimer of MnO 6 octahedra. The magnetic susceptibility shows magnetic cluster behavior, with cluster formation temperature ∼220 K. Antiferromagnetic order has been observed at T N ∼ 6 K. Ba 4 Sn 1.1 Mn 2.9 O 12 is a semiconductor with a transport activation energy of 0.61 eV.