Resonant x-ray scattering in 3d-transition-metal oxides: Anisotropy and charge orderings

TL;DR

This paper reviews how resonant x-ray scattering (RXS) is used to investigate electronic anisotropy and charge orderings in 3d-transition-metal oxides, revealing symmetry breaking and structural distortions.

Contribution

It discusses the application of RXS at the K edge to detect local anisotropy and charge disproportionation, highlighting its effectiveness in studying electronic orderings in transition-metal oxides.

Findings

RXS reveals charge ordering in manganites, Fe3O4, and ferrites.

Detection of forbidden reflections and anisotropy in various oxides.

Electronic orderings are linked to structural distortions.

Abstract

The structural, magnetic and electronic properties of transition metal oxides reflect in atomic charge, spin and orbital degrees of freedom. Resonant x-ray scattering (RXS) allows us to perform an accurate investigation of all these electronic degrees. RXS combines high-Q resolution x-ray diffraction with the properties of the resonance providing information similar to that obtained by atomic spectroscopy (element selectivity and a large enhancement of scattering amplitude for this particular element and sensitivity to the symmetry of the electronic levels through the multipole electric transitions). Since electronic states are coupled to the local symmetry, RXS reveals the occurrence of symmetry breaking effects such as lattice distortions, onset of electronic orbital ordering or ordering of electronic charge distributions. We shall discuss the strength of RXS at the K absorption edge of 3d transition-metal oxides by describing various applications in the observation of local anisotropy and charge disproportionation. Examples of these resonant effects are (I) charge ordering transitions in manganites, Fe3O4 and ferrites and (II) forbidden reflections and anisotropy in Mn3+ perovskites, spinel ferrites and cobalt oxides. In all the studied cases, the electronic (charge and/or anisotropy) orderings are determined by the structural distortions.