75As NMR local probe study of magnetism in (Eu1-xKx)Fe2As2

TL;DR

This study uses 75As NMR to investigate how Eu2+ magnetic moments influence the local magnetic environment and relaxation processes in (Eu1-xKx)Fe2As2 across different doping levels.

Contribution

It provides detailed insights into the local magnetic interactions and the effects of Eu doping on NMR properties in EuFe2As2-based superconductors.

Findings

Eu2+ moments dominate NMR properties and cause broad linewidths.

Increasing Eu content reduces NMR signal intensity, disappearing at full Eu doping.

Spin-lattice relaxation rate is influenced by Eu2+ fluctuations and superconductivity.

Abstract

75As NMR measurements were performed as a function of temperature and doping in (Eu1-xKx)Fe2As2 (x=0,0.38,0.5,0.7) samples. The large Eu2+ moments and their fluctuations are found to dominate the 75As NMR properties. The 75As nuclei close to the Eu2+ moments likely have a very short spin-spin relaxation time (T2) and are wiped out of our measurement window. The 75As nuclei relatively far from Eu2+ moments are probed in this study. Increasing the Eu content progressively decreases the signal intensity with no signal found for the full-Eu sample (x=0). The large 75As NMR linewidth arises from an inhomogeneous magnetic environment around them. The spin lattice relaxation rate (1/T1) for x=0.5 and 0.7 samples is nearly independent of temperature above 100K and results from a coupling to paramagnetic fluctuations of the Eu2+ moments. The behavior of 1/T1 at lower temperatures has contributions from the antiferromagnetic fluctuations of the Eu2+ moments as also the fluctuations intrinsic to the FeAs planes and from superconductivity.