M\"ossbauer spectroscopy study of magnetic fluctuations in superconducting RbGd$_2$Fe$_4$As$_4$O$_2$

TL;DR

This study uses Mössbauer spectroscopy to investigate magnetic fluctuations in the superconducting RbGd$_2$Fe$_4$As$_4$O$_2$, revealing no static magnetic order but detecting magnetic fluctuations linked to Gd$^{3+}$ and Fe moments.

Contribution

It provides new insights into the magnetic fluctuation behavior in a self-doped iron-based superconductor using temperature-dependent Mössbauer spectra.

Findings

No static magnetic order observed at Fe sites.

Magnetic fluctuations detected below 15 K and 100 K.

Self doping alters local electronic structure.

Abstract

$^{57}$Fe M\"ossbauer spectra were measured at different temperatures between 5.9 K and 300 K on the recently discovered self-doped superconducting RbGd$_2$Fe$_4$As$_4$O$_2$ with T$_c$ as high as 35 K. Singlet pattern was observed down to the lowest temperature measured in this work, indicating the absence of static magnetic order on the Fe site. The intermediate isomer shift in comparison with that of the samples RbFe$_2$As$_2$ and GdFeAsO confirms the self doping induced local electronic structure change. Surprisingly, we observe two magnetic fluctuation induced spectral broadenings below $\sim$15 K and $\sim$100 K which are believed to be originated from the transferred magnetic fluctuations of the Gd$^{3+}$ moments and that of the magnetic fluctuations of the Fe atoms, respectively.