title: Competing exchange interactions on the verge of a metal-insulator transition in the two-dimensional spiral magnet Sr3Fe2O7.
abstract: We report a neutron scattering study of the magnetic order and dynamics of the bilayer perovskite Sr(3)Fe(2)O(7), which exhibits a temperature-driven metal-insulator transition at 340 K. We show that the Fe(4+) moments adopt incommensurate spiral order below T(N) = 115 K and provide a comprehensive description of the corresponding spin-wave excitations. The observed magnetic order and excitation spectra can be well understood in terms of an effective spin Hamiltonian with interactions ranging up to third-nearest-neighbor pairs. The results indicate that the helical magnetism in Sr(3)Fe(2)O(7) results from competition between ferromagnetic double-exchange and antiferromagnetic superexchange interactions whose strengths become comparable near the metal-insulator transition. They thus confirm a decades-old theoretical prediction and provide a firm experimental basis for models of magnetic correlations in strongly correlated metals.
authors.affiliation: Max-Planck-Institut für Festkörperforschung, D-70569 Stuttgart, Germany.
authors.forename: J-H
authors.initials: JH
authors.lastname: Kim
authors.affiliation: Max-Planck-Institut für Festkörperforschung, D-70569 Stuttgart, Germany and Solid State Physics Division, Bhabha Atomic Research Centre, Mumbai 400085, India.
authors.forename: Anil
authors.initials: A
authors.lastname: Jain
authors.affiliation: Helmholtz-Zentrum Berlin für Materialien und Energie, D-14109 Berlin, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Reehuis
authors.affiliation: Max-Planck-Institut für Festkörperforschung, D-70569 Stuttgart, Germany.
authors.forename: G
authors.initials: G
authors.lastname: Khaliullin
authors.affiliation: Max-Planck-Institut für Festkörperforschung, D-70569 Stuttgart, Germany.
authors.forename: D C
authors.initials: DC
authors.lastname: Peets
authors.affiliation: Max-Planck-Institut für Festkörperforschung, D-70569 Stuttgart, Germany and School of Physics, University of New South Wales, Sydney, New South Wales 2052, Australia and Australian Nuclear Science and Technology Organisation, Lucas Heights, New South Wales 2234, Australia.
authors.forename: C
authors.initials: C
authors.lastname: Ulrich
authors.affiliation: Forschungsneutronenquelle Heinz Maier-Leibnitz (FRM-II), D-85748 Garching, Germany.
authors.forename: J T
authors.initials: JT
authors.lastname: Park
authors.affiliation: Forschungsneutronenquelle Heinz Maier-Leibnitz (FRM-II), D-85748 Garching, Germany.
authors.forename: E
authors.initials: E
authors.lastname: Faulhaber
authors.affiliation: Helmholtz-Zentrum Berlin für Materialien und Energie, D-14109 Berlin, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Hoser
authors.affiliation: ISIS Facility, STFC, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11-0QX, United Kingdom.
authors.forename: H C
authors.initials: HC
authors.lastname: Walker
authors.affiliation: ISIS Facility, STFC, Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire OX11-0QX, United Kingdom and Physics Department, Highly Correlated Matter Research Group, University of Johannesburg, P.O. Box 524, Auckland Park 2006, South Africa.
authors.forename: D T
authors.initials: DT
authors.lastname: Adroja
authors.affiliation: Max-Planck-Institut für Festkörperforschung, D-70569 Stuttgart, Germany.
authors.forename: A C
authors.initials: AC
authors.lastname: Walters
authors.affiliation: Max-Planck-Institut für Festkörperforschung, D-70569 Stuttgart, Germany and Institut für Festkörperphysik, TU Dresden, D-01069 Dresden, Germany.
authors.forename: D S
authors.initials: DS
authors.lastname: Inosov
authors.affiliation: Max-Planck-Institut für Festkörperforschung, D-70569 Stuttgart, Germany and Leibniz Institut für Festkörper-und Werkstoffforschung, D-01171 Dresden, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Maljuk
authors.affiliation: Max-Planck-Institut für Festkörperforschung, D-70569 Stuttgart, Germany.
authors.forename: B
authors.initials: B
authors.lastname: Keimer