Muon spin relaxation studies of magnetic order and superfluid density in antiferromagnetic NdOFeAs, BaFe2As2 and superconducting (Ba,K)Fe2As2

TL;DR

This study uses muon spin relaxation to investigate magnetic order and superfluid density in various iron-based compounds, revealing coexistence of magnetism and superconductivity with different magnetic structures.

Contribution

It provides new insights into the magnetic and superconducting coexistence in NdOFeAs, BaFe2As2, and (Ba,K)Fe2As2 using muon spin relaxation measurements.

Findings

NdOFeAs shows static magnetic order below 135 K.

Superconducting (Ba,K)Fe2As2 exhibits coexistence of magnetism and superconductivity.

Magnetic order varies from commensurate to incommensurate or short-ranged.

Abstract

Zero-field (ZF) muon spin relaxation ($\mu$SR) measurements have revealed static commensurate magnetic order of Fe moments in NdOFeAs below $T_{N} \sim 135$ K, with the ordered moment size nearly equal to that in LaOFeAs, and confirmed similar behavior in BaFe$_{2}$As$_{2}$. In single crystals of superconducting (Ba$_{0.55}$K$_{0.45}$)Fe$_{2}$As$_{2}$, $\mu$SR spectra indicate static magnetism with incommensurate or short-ranged spin structure in $\sim$ 70 % of volume below $T_{N} \sim$ 80 K, coexisting with remaining volume which exhibits superfluid-response consistent with nodeless gap below $T_{c}\sim 30$ K.