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Home page > LPCNO > Seminars > 2011 > Neutron scattering: a probe for magnetism and superconductivity.

Neutron scattering: a probe for magnetism and superconductivity.

Date : 13/09/2011 à 14:00

Titre : Neutron scattering: a probe for magnetism and superconductivity.

Intervenant : Mark Laver

Provenance : Materials Research Division, Risø DTU, Technical University of Denmark, Roskilde, Denmark ; Nano-Science Center, Niels Bohr Institute, University of Copenhagen, Denmark ; Laboratory for Neutron Scattering, Paul Scherrer Institut, Villigen, Switzerland

Salle : Salle 29 (RdC)

Résumé: Neutron scattering probes the bulk of systems, but also thin films and confined environments. In this talk, topical studies are overviewed, using both polarised and unpolarised beams. The small-angle scattering technique, which measures nanoscale features, is encountered frequently and introduced using nanoparticles as an example.

Small-angle neutron scattering is invaluable for studies of the flux line (FL) lattice in superconductors. By itself the FL system can be exploited as a test-bed for theories of structural order in solids and glasses. Further, the study of FL lattice shapes is useful as a probe of the underlying superconducting state. This is discussed in an overview of recent explorations of superconductors ranging from elemental niobium to the iron pnictides and the cuprates.1,2

The nature of the interaction between the neutron and atomic moments may be used to deduce the magnetization direction. This is illustrated with recent results on an exchange-biased film,3 where magnetic domains with moments perpendicular to the applied field are clearly observed at the exchange bias field. Insight into the magnetic structure may additionally be realised by analyzing the polarization state of the scattering neutron. In the room-temperature multiferroic material BiFeO3, our neutron polarisation studies unveil a spin-density wave component to the long-wavelength magnetic modulation.4 The significance of this result on the bulk material to technological applications, which are envisaged to use strained films, is discussed.

1 in close collaboration with J. Chang, J. S. White, S. M. Hayden, E. M. Forgan, and J. Mesot. 2 M. Laver and E. M. Forgan, Nature Comms. 1, 45 (2011). 3 C. Dufour, M. R. Fitzsimmons, J. A. Borchers, M. Laver, K. L. Krycka, K. Dumesnil, S. M. Watson, W. C. Chen, J. Won, and S. Singh, Phys. Rev. B 84, 064420 (2011). 4 in close collaboration with M. Ramazanoglu, W. Ratcliff II, S. M. Watson, W. C. Chen, A. Jackson, K. Kothapalli, S. Lee, S. W. Cheong, and V. Kiryukhin.