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
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
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)
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  MCP direction makes our occupancy analysis particularly robust because of symmetry constraints.Changes in occupancy give dramatic structural response to the onset of ferromagnetism.