Slow magnetic fluctuations and superconductivity in fluorine-doped NdFeAsO

TL;DR

This study investigates the magnetic and superconducting properties of NdFeAsO with fluorine doping, revealing slow magnetic fluctuations and a transition from long-range to short-range magnetic order near the onset of superconductivity.

Contribution

It provides the first systematic analysis of the crossover region between magnetism and superconductivity in NdFeAsO with fluorine doping using muon-spin spectroscopy and magnetometry.

Findings

Short-range magnetic interactions emerge at x=0.08 doping.

Slow magnetic fluctuations are observed near the superconducting transition.

Magnetic fluctuations disappear at low temperatures.

Abstract

Among the widely studied superconducting iron-pnictide compounds belonging to the Ln1111 family (with Ln a lanthanide), a systematic investigation of the crossover region between the superconducting and the antiferromagnetic phase for the Ln = Nd case has been missing. We fill this gap by focusing on the intermediate doping regime of NdFeAsO(1-x)F(x) by means of dc-magnetometry and muon-spin spectroscopy measurements. The long-range order we detect at low fluorine doping is replaced by short-range magnetic interactions at x = 0.08, where also superconductivity appears. In this case, longitudinal-field muon-spin spectroscopy experiments show clear evidence of slow magnetic fluctuations that disappear at low temperatures. This fluctuating component is ascribed to the glassy-like character of the magnetically ordered phase of NdFeAsO at intermediate fluorine doping.