Magnetism and Disorder Effects on muSR Measurements of the Magnetic Penetration Depth in Iron-Based Superconductors

TL;DR

This paper demonstrates that field-induced magnetic order and vortex-lattice disorder significantly hinder accurate measurements of the magnetic penetration depth in iron-based superconductors using TF-muSR, leading to uncertainties.

Contribution

It reveals the impact of magnetic order and vortex disorder on muSR measurements, highlighting limitations in current methods for iron-based superconductors.

Findings

Field-induced magnetic order affects muSR measurements.

Vortex-lattice disorder causes deviations in magnetic field distribution.

Uncertainty in penetration depth values is introduced by these effects.

Abstract

It is shown that attempts to accurately deduce the magnetic penetration depth of overdoped BaFe_{1.82}Co_{0.18}As2 single crystals by transverse-field muon spin rotation (TF-muSR) are thwarted by field-induced magnetic order and strong vortex-lattice disorder. We explain how substantial deviations from the magnetic field distribution of a nearly perfect vortex lattice by one or both of these factors is also significant for other iron-based superconductors, and this introduces considerable uncertainty in the values of the magnetic penetration depth obtained by TF-muSR.