title: Single-ion anisotropy and exchange interactions in the cyano-bridged trimers MnIII2MIII(CN)6 (MIII = Co, Cr, Fe) species incorporating [Mn(5-Brsalen)]+ units: an inelastic neutron scattering and magnetic susceptibility study.
abstract: The electronic structures of the compounds K[(5-Brsalen)(2)(H(2)O)(2)-Mn(2)M(III)(CN)(6)].2H(2)O (M(III) = Co(III), Cr(III), Fe(III)) have been determined by inelastic neutron scattering (INS) and magnetic susceptibility studies, revealing the manganese(III) single-ion anisotropy and exchange interactions that define the low-lying states of the Mn-M(III)-Mn trimeric units. Despite the presence of an antiferromagnetic intertrimer interaction, the experimental evidence supports the classification of both the Cr(III) and Fe(III) compounds as single-molecule magnets. The value of 17(2) cm(-1) established from AC susceptibility measurements for a spin-reversal barrier of K[(5-Brsalen)(2)(H(2)O)(2)-Mn(2)Cr(CN)(6)].2H(2)O may be readily rationalized in terms of the energy level diagram determined directly by INS. AC susceptibility measurements on samples of K[(5-Brsalen)(2)(H(2)O)(2)-Mn(2)Fe(CN)(6)].2H(2)O are contrary to those previously reported, exhibiting but the onset of peaks below temperatures of 1.8 K at oscillating frequencies in the range of 100-800 Hz. INS measurements reveal an anisotropic ferromagnetic manganese(III)-iron(III) exchange interaction, in accordance with theoretical expectations based on the unquenched orbital angular momentum of the [Fe(CN)(6)](3-) anion, giving rise to an M(s) approximately +/-9/2 ground state, isolated by approximately 11.5 cm(-1) from the higher-lying levels. The reported INS and magnetic data should now serve as a benchmark against which theoretical models that aim to inter-relate the electronic and molecular structure of molecular magnets should be tested.
authors.affiliation: Laboratory for Neutron Scattering, ETH Zurich and Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland. philip.tregenna@psi.ch
authors.forename: Philip L W
authors.initials: PL
authors.lastname: Tregenna-Piggott
authors.forename: Denis
authors.initials: D
authors.lastname: Sheptyakov
authors.forename: Lukas
authors.initials: L
authors.lastname: Keller
authors.forename: Sophia I
authors.initials: SI
authors.lastname: Klokishner
authors.forename: Sergei M
authors.initials: SM
authors.lastname: Ostrovsky
authors.forename: Andrei V
authors.initials: AV
authors.lastname: Palii
authors.forename: Oleg S
authors.initials: OS
authors.lastname: Reu
authors.forename: Jesper
authors.initials: J
authors.lastname: Bendix
authors.forename: Theis
authors.initials: T
authors.lastname: Brock-Nannestad
authors.forename: Kasper
authors.initials: K
authors.lastname: Pedersen
authors.forename: Høgni
authors.initials: H
authors.lastname: Weihe
authors.forename: Hannu
authors.initials: H
authors.lastname: Mutka