title: Crystal structure and magnetism of Fe2(OH)[B2O4(OH)].
abstract: The structure and magnetism of Fe2(OH)[B2O4(OH)] are reported. Powder x-ray diffraction reveals a characteristic structure containing two crystallographically independent zigzag-ladder chains of magnetic Fe(2+) ions. Magnetization measurements reveal a phase transition at 85 K, below which a weak spontaneous magnetization (≈ 0.15 μB/Fe) appears. Below 85 K, magnetization increases with decreasing temperature down to 70 K, below which it decreases and approaches a constant value at low temperature. The Mössbauer spectrum at room temperature is composed of two paramagnetic doublets corresponding to the two crystallographic Fe(2+) sites. Below 85 K, each doublet undergoes further splitting because of the magnetic hyperfine fields. The temperature dependence of the hyperfine field is qualitatively different for the two distinguishable Fe(2+) sites. This is responsible for the anomalous temperature dependence of the magnetization.
authors.affiliation: Department of Physics, Chuo University, 1-13-27 Kasuga, Bunkyo-ku, Tokyo 112-8551, Japan.
authors.forename: Yotaro
authors.initials: Y
authors.lastname: Kurayoshi
authors.forename: Shigeo
authors.initials: S
authors.lastname: Hara
authors.forename: Hirohiko
authors.initials: H
authors.lastname: Sato
authors.forename: Cathrine
authors.initials: C
authors.lastname: Frandsen
authors.forename: Steen
authors.initials: S
authors.lastname: Mørup
authors.forename: Helge Kildahl
authors.initials: HK
authors.lastname: Rasmussen
authors.forename: Shin
authors.initials: S
authors.lastname: Nakamura