Determination of characteristic muon precession and relaxation signals in FeAs and FeAs2, possible impurity phases in pnictide superconductors

TL;DR

This study uses muon-spin relaxation to characterize magnetic signals in FeAs and FeAs2, impurity phases in pnictide superconductors, clarifying their magnetic properties and ruling out their influence on prior measurements.

Contribution

It provides detailed muon-spin relaxation data on FeAs and FeAs2, clarifying their magnetic behavior and excluding their impact on previous superconductor studies.

Findings

FeAs shows well-defined muon precession with two frequencies.

FeAs2 lacks long-range magnetic order above 2 K.

Results exclude impurity effects in prior pnictide superconductor measurements.

Abstract

We report muon-spin relaxation measurements of highly homogeneous samples of FeAs and FeAs2, both previously found as impurity phases in some samples of recently synthesized pnictide superconductors. We observe well defined muon precession in the FeAs sample with two precession frequencies of 38.2(3) and 22.7(9) MHz at 7.5 K, with the majority of the amplitude corresponding to the lower frequency component. In FeAs2 we confirm previous measurements showing that no long-ranged magnetic order occurs above 2 K and measure the muon spin relaxation rate, which increases on cooling. Our results exclude the possibility that previous muon-spin relaxation measurements of pnictide superconductors have been measuring the effect of these possible impurities.