SPring-8, the large synchrotron radiation facility

Date & Time: 13:30-15:00, October 4, 2005

Speaker: Dr. Stuart Wilkins
Affiliation: ESRF

Abstract
　　Orbital ordering occurs when long-range order of anisotropic charge distributions develops in a material. Noted systems where this has been studied are the manganites [1], where long range ordering of the 3d electrons have been discovered and UPd3 [2] where the 5f electrons are shown to long-range order. Neutron diffraction is not sensitive to such effects, but resonance x-ray scattering (RXS) at an elemental absorption edge, combined with an analysis of the outgoing polarization as a function of the azimuthal angle, is particularly powerful. We report here experiments on both the magnanites La0.5Sr1.5MnO4 [1] and LaSr2Mn2O7 [3] and the actinide oxides UO2 [4] and NpO2 [5], as well as a mixed (U,Np)O2 system [6].

1: S. B. Wilkins et al., PRL 91 (2003) 167205
2: D. McMorrow et al., PRL 87 (2001) 057201
3: S. B. Wilkins et al., submitted to Physical Review Letters
4: S. B. Wilkins et al., submitted to Physical Review Letters
5: J. A. Paixao et al, PRL 89 (2002) 187202
6: S. B. Wilkins et al. PR B 70 (2004) 214402