Soft X-ray resonant scattering study of single-crystal LaSr$_2$Mn$_2$O$_7$

TL;DR

This study uses soft X-ray resonant scattering to investigate the electronic and magnetic structures of LaSr$_2$Mn$_2$O$_7$, revealing complex valence states, polarization-dependent resonances, and coupling between charge and orbital orderings.

Contribution

It provides detailed insights into the electronic states and their temperature-dependent behavior in LaSr$_2$Mn$_2$O$_7$ using resonant scattering at multiple edges, highlighting complex valence and ordering phenomena.

Findings

Resonant enhancement at Mn edges indicates mixed valence states.

Polarization dependence reveals complex electronic origins.

Charge Bragg reflection shows anomalies near orbital-ordering transition.

Abstract

Soft X-ray resonant scattering studies at the Mn $L_{\texttt{II, III}}$- and the La $M_{\texttt{IV, V}}$- edges of single-crystal LaSr$_2$Mn$_2$O$_7$ are reported. At low temperatures, below $T_\texttt{N} \approx 160$ K, energy scans with a fixed momentum transfer at the \emph{A}-type antiferromagnetic (0 0 1) reflection around the Mn $L_{\texttt{II, III}}$-edges with incident linear $\sigma$ and $\pi$ polarizations show strong resonant enhancements. The splitting of the energy spectra around the Mn $L_{\texttt{II, III}}$-edges may indicate the presence of a mixed valence state, e.g., Mn$^{3+}$/Mn$^{4+}$. The relative intensities of the resonance and the clear shoulder-feature as well as the strong incident $\sigma$ and $\pi$ polarization dependences strongly indicate its complex electronic origin. Unexpected enhancement of the charge Bragg (0 0 2) reflection at the La $M_{\texttt{IV, V}}$-edges with $\sigma$ polarization has been observed up to 300 K, with an anomaly appearing around the orbital-ordering transition temperature, $T_{\texttt{OO}} \approx 220$ K, suggesting a strong coupling (competition) between them.