title: Two-dimensional charge disproportionation of the unusual high valence state Fe(4+) in a layered double perovskite.
abstract: The crystal and magnetic structures of charge-disproportionated Ca2FeMnO6 were analyzed by neutron powder diffraction. Ca2FeMnO6 is a layered double perovskite oxide with a two-dimensional arrangement of Mn(4+) and unusual high valence Fe(4+) at room temperature. When cooled, the compound shows charge disproportionation followed by magnetic transition. Around 200 K, the Fe(4+) shows the charge disproportionation to Fe(3+) and Fe(5+), which are ordered in a checkerboard pattern in the two-dimensional FeO6 octahedral layers. The magnetic transition occurs at 95 K, which is much lower than the charge disproportionation temperature. The magnetic structure is commensurate but noncollinear, and the antiferromagnetic coupling of Fe(3+) and Fe(5+) spins in the FeO6 octahedral layers gives the ferrimagnetic moments. The unique magnetic structure is described as a result of two-dimensional localization of the ligand holes with effective spins.
authors.affiliation: †Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan.
authors.forename: Yoshiteru
authors.initials: Y
authors.lastname: Hosaka
authors.affiliation: †Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan.
authors.forename: Noriya
authors.initials: N
authors.lastname: Ichikawa
authors.affiliation: †Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Saito
authors.affiliation: ‡ISIS, Rutherford Appleton Laboratory, Harwell Oxford, Didcot OX11 0QX, United Kingdom.
authors.forename: Pascal
authors.initials: P
authors.lastname: Manuel
authors.affiliation: ‡ISIS, Rutherford Appleton Laboratory, Harwell Oxford, Didcot OX11 0QX, United Kingdom.
authors.forename: Dmitry
authors.initials: D
authors.lastname: Khalyavin
authors.affiliation: §Centre for Science at Extreme Conditions and School of Chemistry, University of Edinburgh, Mayfield Road, Edinburgh EH9 3JZ, United Kingdom.
authors.forename: J Paul
authors.initials: JP
authors.lastname: Attfield
authors.affiliation: †Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan.|∥Japan Science and Technology Agency, CREST, Uji, Kyoto 611-0011, Japan.
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Shimakawa