Charge and magnetic X-ray scattering

Abstract

The hole doped transition metal oxides show remarkable properties that are related to the influence of charge and spin correlations. In this thesis charge correlations in hole doped manganite and nickelate systems are smdied using soft (˂2 keV), normal (10 keV) and high energy x-ray scattering (100 keV).The charge and J aim-Teller (JT) order is studied in the bi-layer manganite La(_2)-(_2r) Sr(_1)+(_2x)Mn(_2)O(_7) for x = 0.5, 0.55 and 0.60 using high energy x-ray scattering. In the x = 0.55 sample the charge ordered state existed in the same checkerboard pattern as observed in the x = 0.5 sample with no change in behaviour. However, in the x = 0.6 doped sample the charge ordered state entered a new regime characterised by incommensurate JT and charge order. The magnitude of the incommensurability was inversely proportional to the intensity of the JT and charge peaks. High resolution x-ray measurements of the charge stripe order in the La(_2-x)Sr(_x)NiO(_4) system in the doping range 0.20 ≤ x ≤ 0.50 are presented. As the doping was moved away in either direction from the commensurate x = 0.33 the charge stripes changed from a highly correlated state to an increasingly disordered charge glass state. At the commensurate 0.5 composition there was no increase in the intensity or correlation of the charge order despite a significantly higher transition temperature than in the lower doped compositions. Finally the first measurements of the orbital order in La(_0.5)Sr(_1.5) MnO(_4) using soft x-ray scattering at the manganese L edges are presented. The measurements directly probe the orbital order unlike the previously reported measurements at the manganese K-edge. Energy scans were carried out on the orbital order and compared with theoretical predictions. From this it was determined that both the Jahn-Teller distortions and direct orbital ordering contribute to the observed scattering.