Crystal Structures and Magnetic Properties of the Manganese Oxide Chlorides Sr2MnO3Cl and Sr4Mn3O8-yCl2

The crystal structures of the manganese oxide chlorides Sr 2 MnO 3 Cl and Sr 4 Mn 3 O 8 - y Cl 2 have been determined from neutron powder diffraction data collected at room temperature and at 2 K. The materials crystallize in the tetragonal space groups P 4/ nmm (Sr 2 MnO 3 Cl) and I 4/ mmm (Sr 4 Mn 3 O 8 - y Cl 2 ) and the structures are analogous to the n = 1 and n = 3 Ruddlesden−Popper phases Sr 2 MnO 4 and Ca 4 Mn 3 O 10 . Both materials contain layers of highly distorted Mn(III)O 5 Cl octahedra. Sr 4 Mn 3 O 8 - y Cl 2, in addition, has a central layer of MnO 6 - δ octahedra with oxygen vacancies localized within the tetragonal plane. Consequently, the average coordination of the site is reduced to a mixture of 6-fold and 5-fold and some of the Mn atoms adopt pyramidal coordination. The level of oxygen deficiency within Sr 4 Mn 3 O 8 - y Cl 2 y = 0.44 confirms the Mn valence is predominantly +3. Magnetic susceptibility measurements indicate the onset of antiferromagnetic ordering ( T AF ) in the materials at 80 and 90 K for Sr 2 MnO 3 Cl and Sr 4 Mn 3 O 8 - y Cl 2, respectively. Antiferromagnetic order is confirmed by the presence of magnetic scattering in the low-temperature neutron diffraction data. The magnetic structure of Sr 2 MnO 3 Cl has been determined, yielding an ordered manganese moment μ z = 3.74(5) μ B at 2 K. In contrast, the magnetic scattering exhibited by Sr 4 Mn 3 O 8 - y Cl 2 suggests a level of magnetic frustration.