title: Light-induced spin-crossover magnet.
abstract: The light-induced phase transition between the low-spin (LS) and high-spin (HS) states of some transition-metal ions has been extensively studied in the fields of chemistry and materials science. In a crystalline extended system, magnetically ordering the HS sites of such transition-metal ions by irradiation should lead to spontaneous magnetization. Previous examples of light-induced ordering have typically occurred by means of an intermetallic charge transfer mechanism, inducing a change of valence of the metal centres. Here, we describe the long-range magnetic ordering of the extended Fe(II)(HS) sites in a metal-organic framework caused instead by a light-induced excited spin-state trapping effect. The Fe-Nb-based material behaves as a spin-crossover magnet, in which a strong superexchange interaction (magnetic coupling through non-magnetic elements) between photo-produced Fe(II)(HS) and neighbouring Nb(IV) atoms operates through CN bridges. The magnetic phase transition is observed at 20 K with a coercive field of 240 Oe.
authors.affiliation: Department of Chemistry, School of Science, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan. ohkoshi@chem.s.u-tokyo.ac.jp
authors.forename: Shin-Ichi
authors.initials: S
authors.lastname: Ohkoshi
authors.forename: Kenta
authors.initials: K
authors.lastname: Imoto
authors.forename: Yoshihide
authors.initials: Y
authors.lastname: Tsunobuchi
authors.forename: Shinjiro
authors.initials: S
authors.lastname: Takano
authors.forename: Hiroko
authors.initials: H
authors.lastname: Tokoro
mesh_terms: D018360:Crystallography, X-Ray; D007501:Iron / Q000737:chemistry*; D008027:Light; D008280:Magnetics; D008958:Models, Molecular; D015394:Molecular Structure; D009556:Niobium / Q000737:chemistry*; D009942:Organometallic Compounds / Q000737:chemistry*; D044367:Phase Transition
chemical_list: D009942:Organometallic Compounds; D009556:Niobium; D007501:Iron