High-field electron spin resonance spectroscopy study of GdO$_{1-x}$F$_{x}$FeAs superconductors

TL;DR

This study uses high-field electron spin resonance to investigate magnetic properties and their evolution in GdO$_{1-x}$F$_{x}$FeAs superconductors, revealing magnetic correlations and coupling effects related to superconductivity.

Contribution

It provides new insights into the magnetic interactions and short-range correlations in doped Fe-based superconductors using high-field ESR techniques.

Findings

Parent compound shows Fe magnetic order below 128 K.

Doped samples are superconducting with T$_c$ up to 45 K.

Short-range magnetic correlations exist in superconducting samples.

Abstract

We report a detailed investigation of GdO$_{1-x}$F$_{x}$FeAs (x = 0, 0.07 and 0.14) samples by means of high-field/high-frequency electron spin resonance (HF-ESR) together with measurements of thermodynamic and transport properties. The parent GdOFeAs compound exhibits Fe long-range magnetic order below 128 K, whereas both doped samples do not show such order and are superconducting with T$_c$ = 20 K (x = 0.07) and T$_c$ = 45 K (x = 0.14). The Gd$^{3+}$ HF-ESR reveals an appreciable exchange coupling between Gd and Fe moments, through which the static magnetic order is clearly seen in the parent compound. Owing to this coupling, HF-ESR can probe sensitively the evolution of the magnetism in the FeAs planes upon F doping. It is found that in both superconducting samples, where the Fe long-range order is absent, there are short-range, static on the ESR time scale magnetic correlations between Fe spins. Their occurrence on a large doping scale may be indicative of the ground states' coexistence.