Browsing by Author "Walker, HC"

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    Competing exchange interactions on the verge of a metal-insulator transition in the two-dimensional spiral magnet Sr3Fe2O7
    (Americal Physical Society, 2014-10-03) Kim, JH; Jain, A; Reehuis, M; Khaliullin, G; Peets, DC; Ulrich, C; Park, JT; Faulhaber, E; Hoser, A; Walker, HC; Adroja, DT; Walters, AC; Inosov, DS; Maljuk, A; Keimer, B
    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. © 2014, American Physical Society.
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    Magnetic structure and magnon dynamics of the quasi-two-dimensional antiferromagnet FePS 3
    (American Physical Society, 2016-12-07) Lançon, D; Walker, HC; Ressouche, E; Ouladdiaf, B; Rule, KC; McIntyre, GJ; Hicks, TJ; Rønnow, HM; Wildes, AR
    Neutron scattering from single crystals has been used to determine the magnetic structure and magnon dynamics of FePS3, an S=2 Ising-like quasi-two-dimensional antiferromagnet with a honeycomb lattice. The magnetic structure has been confirmed to have a magnetic propagation vector of kM=[0112] and the moments are collinear with the normal to the ab planes. The magnon data could be modeled using a Heisenberg Hamiltonian with a single-ion anisotropy. Magnetic interactions up to the third in-plane nearest neighbor needed to be included for a suitable fit. The best fit parameters for the in-plane exchange interactions were J1=1.46, J2=−0.04, and J3=−0.96 meV. The single-ion anisotropy is large, Δ=2.66 meV, explaining the Ising-like behavior of the magnetism in the compound. The interlayer exchange is very small, J′=−0.0073 meV, proving that FePS3 is a very good approximation to a two-dimensional magnet. ©2016 American Physical Society
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    REXS contribution to electronic ordering investigation in solids
    (Springer Heidelberg, 2012-06-01) Beale, TAW; Beutier, G; Bland, SR; Bombardi, A; Bouchenoire, L; Bunau, O; Di Matteo, S; Fernandez-Rodriguez, J; Hamann-Borrero, JE; Herrero-Martin, J; Jacques, VLR; Johnson, RD; Juhin, A; Matsumura, T; Mazzoli, C; Mulders, AM; Nakao, H; Okamoto, J; Partzsch, S; Princep, AJ; Scagnoli, V; Strempfer, J; Vecchini, C; Wakabayashi, Y; Walker, HC; Wermeille, D; Yamasaki, Y
    Resonant Elastic X-Ray Scattering (REXS) has played a fundamental role in understanding electronic properties and in revealing hidden order, local symmetries and exotic states realized in correlated solids. This article reports on some of the relevant scientific contributions and technical advances over the last 20 years, by providing a list of related publications produced by various groups all around the world. The given perspective is that of a group of young scientists involved at various times in the investigation of the beauty of electronic ordering by the REXS technique. © 2012, Springer.