Evidence of Orbital Ordering in Jahn-Teller Undistorted LaSr${}_2$Mn${}_2$O${}_7$

Abstract

Resonant soft x-ray diffraction has been used to probe the temperature dependent orbital and magnetic structure of $\mathrm{LaS}{\mathrm{r}}_2\mathrm{M}{\mathrm{n}}_2{\mathrm{O}}_7$. Previous crystallographic studies have shown that this material has almost no MnO${}_6$ oxygen displacement due to Jahn-Teller distortions at low temperatures. Within the low-temperature A-type antiferromagnetic phase, we found strong intensity at the $(1/4,1/4,0)$ orbital and $LaS{r}_{2}M{n}_2{O}_7$ magnetic reflections. This shows that even in the near absence of Jahn-Teller distortion, this compound is strongly orbitally ordered. A fit to the Mn $L$-edge resonance spectra demonstrates the presence of orbital ordering of the Mn${}^{3+}$ ions with virtually no Jahn-Teller crystal field in addition to possible Mn${}^{3+}$ and Mn${}^{2+}$~like valence fluctuations.

Accepted for publication in Journal of Physics:Condensed Matter as a letter to the editor