Soft x-ray resonant diffraction study of magnetic and orbital correlations in a manganite near half-doping

TL;DR

This study uses resonant x-ray diffraction at the Mn L-edge to compare magnetic and orbital correlations in a manganite near half-doping, revealing differences in correlation lengths and spectral weight shifts that challenge traditional models.

Contribution

It provides the first direct comparison of magnetic and orbital correlations in Pr0.6Ca0.4MnO3 using resonant x-ray diffraction, highlighting discrepancies with classical charge-ordering theories.

Findings

Magnetic correlation length exceeds orbital correlation length by nearly a factor of two.

Large (~3 eV) spectral weight shift observed between magnetic and orbital line shapes.

Results challenge the classical Goodenough charge-ordering picture.

Abstract

We have utilized the resonant x-ray diffraction technique at the Mn L-edge in order to directly compare magnetic and orbital correlations in the Mn sub-lattice of Pr0.6Ca0.4MnO3. The resonant line shape is measured below T_OO ~ 240 K at the orbital ordering wave vector (0,1/2,0), and below T_N ~ 175 K at the antiferromagnetic wave vector (1/2,0,0). Comparing the width of the super-lattice peaks at the two wavevectors, we find that the correlation length of the magnetism exceeds that of the orbital order by nearly a factor of two. Furthermore, we observe a large (~ 3 eV) shift in spectral weight between the magnetic and orbital line shapes, which cannot be explained within the classic Goodenough picture of a charge-ordered ground state. To explain the large shift, we calculate the resonant line shapes for orbital and magnetic diffraction based on a relaxed charge-ordered model.