Crystal structures and magnetic properties of the manganese oxide chlorides Sr2MnO3Cl and Sr4Mn3O8-yCl2

Knee, Christopher S., Zhukov, Alexander A. and Weller, Mark T. (2002) Crystal structures and magnetic properties of the manganese oxide chlorides Sr2MnO3Cl and Sr4Mn3O8-yCl2. Chemistry of Materials, 14 (10), 4249-4255. (doi:10.1021/cm020280c).

Abstract

The crystal structures of the manganese oxide chlorides Sr2MnO3Cl and Sr4Mn3O8-yCl2 have been determined from neutron powder diffraction data collected at room temperature and at 2 K. The materials crystallize in the tetragonal space groups P4/nmm (Sr2MnO3Cl) and I4/mmm (Sr4Mn3O8-yCl2) and the structures are analogous to the n = 1 and n = 3 Ruddlesden-Popper phases Sr2MnO4 and Ca4Mn3O10. Both materials contain layers of highly distorted Mn(III)O5Cl octahedra. Sr4Mn3O8-yCl2, in addition, has a central layer of MnO6-delta 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 Sr2MnO3Cl and Sr4Mn3O8-yCl2, respectively. Antiferromagnetic order is confirmed by the presence of magnetic scattering in the low-temperature neutron diffraction data. The magnetic structure of Sr2MnO3Cl has been determined, yielding an ordered manganese moment mu(z) = 3.74(5) mu(B) at 2 K. In contrast, the magnetic scattering exhibited by Sr4Mn3O8-yCl2 suggests a level of magnetic frustration.

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