Magnetism in Two-leg Ladder Compound Ba6Fe8S15 with Mixed Oxidation State of Iron

The magnetic properties of two-leg ladder compound Ba6Fe8S15 were studied to clarify the magnetic state at low temperatures. The 57Fe Mössbauer spectra above 120K indicate the existence of only a single quadrupole doublet, which is consistent with the evidence of one crystallographic Fe site. Below 120K, however, the spectra characterized by two kinds of magnetic hyperfine patterns were observed, indicating an existence of complicated magnetic order. These spectra observed down to 4.2K were analyzed using one-site model of iron where only the hyperfine field is different from each pattern.