Yinwan Li ANL/ UI Chicago P. A. Montano UIChicago/US DOE J. Mitchell ANL

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Temperature-dependent orbital degree of freedom of a bilayer manganite by magnetic Compton scattering. Yinwan Li ANL/ UI Chicago P. A. Montano UIChicago/US DOE J. Mitchell ANL B. Barbiellini, P.E. Mijnarends, S. Kaprzyk and A. Bansil NU Boston. - PowerPoint PPT Presentation

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  • Temperature-dependent orbital degree of freedom of a bilayer manganite by magnetic Compton scattering

    Yinwan Li ANL/ UI Chicago P. A. MontanoUIChicago/US DOEJ. MitchellANLB. Barbiellini, P.E. Mijnarends, S. Kaprzyk and A. Bansil NU Boston

    *Project supported by the U. S. Department of Energy

  • OutlineBi-layer manganiteFerromagnetic phaseMagnetic Momentum densityMagnetic Compton Profile (MCP) along (1 1 0)B(r) overlap integralMain resultsSummary

  • Experimental set-upMeasurements are carried out by flipping the photon polarization SynchrotronRadiation

  • Bilayer Manganite La 1.2 Sr 1.8 Mn2O7Metal-ferromagnetic ~ insulator-paramagnetic Tc=129K

  • Ferromagnetic phase 3d orbitals in a perovskite environnementferromagnetic double exchange coupling between Mn3+ and Mn4+ gives charge delocalizationControl: Temperature, Magnetic field H. At H=7 T we have a homogeneous ferromagnetic phase.

  • Momentum density of d-orbitals

  • Magnetic momentum density

  • MCP along (110)

  • Temperature dependence

  • B(r):Fourier transform of MCP Overlap integral along (110)This minimum gives the x2-y2 occupation

  • Important result The gain of d(z^2) results in an expansion of the apical distance Mn-O (observed in PRB 55, 63 (1997)) and, below Tc, it correlates with FM order.

  • SummaryWe have used a large magnetic field of 7 T which ensures a ferromagnetic homogeneous phase for all studied temperatures. The choice of the [110] MCP direction makes our occupancy analysis particularly robust because of symmetry constraints.Changes in occupancy give dramatic structural response to the onset of ferromagnetism.