X-ray polarization analysis of orbital ordered state in La0.88Sr0.12MnO3

Hole-doped lanthanum manganites La1-xSrxMnO3 have been revisited since the discovery of colossal magnetoresistance (CMR). In this system, orbital as well as spin and charge degrees of freedom have attracted much attention. However, direct observation of orbital ordering (OO) is very difficult and there have been few experiments. Recently, Murakami et al. [Phys. Rev. Lett. 80 (1998) 1932, Phys. Rev. Lett. 81 (1998) 582 ] observed the azimuthal-angle dependence of OO superlattice peaks in La0.5Sr1.5MnO4 and LaMnO3 by resonant x-ray diffraction, which is sensitive to the anisotropy of the structure factor. It is also known that the OO peak changes the polarization of photons from σ to π', which was also observed by Murakami et ai. in LaMnO3. We confirmed that the (0 3 0) reflection of La0.88Sr0.12MnO3 is an OO superlattice peak using synchrotron resonant x-ray diffraction, and then carried out polarization analysis of the OO superlattice peak. While the azimuthal-angle dependence of (0 3 0) shows a clear two-fold dependence, the polarization dependence is somewhat obscure. We found that the beak consists of two parts, one of which shows a σ → π' polarization and the other shows σ → σ' behaviour. We speculate the latter is an extrinsic contamination, though the origin is unknown. (author)