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

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.

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

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

  2. Outline • Bi-layer manganite • Ferromagnetic phase • Magnetic Momentum density • Magnetic Compton Profile (MCP) along (1 1 0) • B(r) overlap integral • Main results • Summary

  3. 3-element Ge Solid State Detector Res.~0.4 a.u. at 100keV Superconductor Magnet Pc=0.64 at Kx=1, Ky=14.4 Slits 11º Silicon Monochromator 50keV, 1= 100keV, 74keV, 125keV Ionization Chamber BESSRC Elliptical Multipole Wiggler B=0~7 Tesla, T=4.2K~300K B Experimental set-up Measurements are carried out by flipping the photon polarization Synchrotron Radiation

  4. La, Sr atoms MnO octahedra Bilayer Manganite La 1.2Sr 1.8Mn2O7 Metal-ferromagnetic ~ insulator-paramagnetic Tc=129K

  5. eg t2g eg t2g Ferromagnetic phase 3d orbitals in a perovskite environnement • ferromagnetic double exchange coupling between Mn3+ and Mn4+ gives charge delocalization Control: Temperature, Magnetic field H. At H=7 T we havea homogeneous ferromagnetic phase.

  6. Momentum density of d-orbitals

  7. Magnetic momentum density

  8. MCP along (110)

  9. Temperature dependence

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

  11. 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.

  12. Summary • We 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.

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