Mössbauer and magnetic studies of mixed-valence linear chain compounds: Na3Fe2S4 and Na3Fe2Se4

Mossbauer and magnetic data establish the two compounds Na3Fe2X4(X=S, Se) as mixed-valence linear chain compounds with rapid valence fluctuation. The compounds exhibit 1-dimensional antiferromagnetic coupling within the chains, and below a critical temperature a 3-dimensional ferrimagnetic ordering between the chains.