Two Magnetic Orderings and a Spin-Flop Transition in Mixed Valence Compound Mn 3 O(SeO 3 ) 3 .

A mixed-valence manganese selenite, Mn 3 O(SeO 3 ) 3 , was successfully synthesized using a conventional hydrothermal method. The three-dimensional framework of this compound is composed of an MnO 6 octahedra and an SeO 3 trigonal pyramid. The magnetic topological arrangement of manganese ions shows a three-dimensional framework formed by the intersection of octa-kagomé spin sublattices and staircase-kagomé spin sublattices. Susceptibility, magnetization and heat capacity measurements confirm that Mn 3 O(SeO 3 ) 3 exhibits two successive long-range antiferromagnetic orderings with T N1 ~4.5 K and T N2 ~45 K and a field-induced spin-flop transition at a critical field of 4.5 T at low temperature.