3 research outputs found
X-ray Resonant Scattering Studies of Orbital and Charge Ordering in PrCaMnO
We present the results of a systematic x-ray scattering study of the charge
and orbital ordering in the manganite series PrCaMnO with
=0.25, 0.4 and 0.5. The temperature dependence of the scattering at the
charge and orbital wavevectors, and of the lattice constants, was characterized
throughout the ordered phase of each sample. It was found that the charge and
orbital order wavevectors are commensurate with the lattice, in striking
contrast to the results of earlier electron diffraction studies of samples with
=0.5. High momentum-transfer resolution studies of the x=0.4 and 0.5 samples
further revealed that while long-range charge order is present, long-range
orbital order is never established. Above the charge/orbital ordering
temperature T, the charge order fluctuations are more highly correlated
than the orbital fluctuations. This suggests that charge order drives orbital
order in these samples. In addition, a longitudinal modulation of the lattice
with the same periodicity as the charge and orbital ordering was discovered in
the x=0.4 and 0.5 samples. For x=0.25, only long-range orbital order was
observed with no indication of charge ordering, nor of an additional lattice
modulation. We also report the results of a preliminary investigation of the
loss of charge and orbital ordering in the x=0.4 sample by application of a
magnetic field. Finally, the polarization and azimuthal dependence of the
charge and orbital ordering in these compounds is characterized both in the
resonant and nonresonant limits, and compared with the predictions of current
theories. The results are qualitatively consistent with both cluster and LDA+U
calculations of the electronic structure.Comment: 37 pages, 22 figure