Synthesis and Magnetic Properties of Two Mixed-Valence Compounds a 2 Mn Ⅱ Mn 2 Ⅲ (SEO 3 ) 6 (A = Sr and Ba)

Two isostructural mixed-valence manganese selenites, A2MnⅡMn2Ⅲ(SeO3)6 (A = Sr and Ba) have been successfully synthesized using a conventional hydrothermal method. These compounds were found to crystallize in the monoclinic space group P21/c, where Mn3+ ions are located in a distorted honeycomb motif centred by the Mn2+ ions. Magnetic measurements suggest that both of two compounds exhibit a similar magnetic behavior, where a short-range and a long-range antiferromagnetic order can be observed at low temperature , while a metamagnetic transition can also be observed under applied field. The UV-vis diffuse reflectance spectra indicate that the band gaps of two compounds are 2.89 eV and 2.82 eV, respectively.