Magnetic fluctuations and spin freezing in nonsuperconducting LiFeAs derivatives

TL;DR

This study investigates magnetic fluctuations and spin freezing in non-superconducting LiFeAs derivatives, revealing different magnetic behaviors and the absence of time-reversal symmetry breaking in stoichiometric LiFeAs.

Contribution

It provides detailed experimental insights into magnetic properties of LiFeAs derivatives, highlighting the absence of triplet pairing signatures and characterizing magnetic fluctuation crossover.

Findings

LiFe$_{1-x}$Ni$_x$As shows weak antiferromagnetic fluctuations

Li$_{1-y}$Fe$_{1+y}$As exhibits a crossover from ferromagnetic to antiferromagnetic fluctuations

No evidence of time-reversal symmetry breaking in LiFeAs

Abstract

We present detailed magnetometry and muon-spin rotation data on polycrystalline samples of overdoped, non-superconducting LiFe$_{1-x}$Ni$_x$As ($x = 0.1,\,0.2$) and Li$_{1-y}$Fe$_{1+y}$As ($0\leq y\leq 0.04$) as well as superconducting LiFeAs. While LiFe$_{1-x}$Ni$_x$As exhibits weak antiferromagnetic fluctuations down to $1.5\,{\rm K}$, Li$_{1-y}$Fe$_{1+y}$As samples, which have a much smaller deviation from the $1:1:1$ stoichiometry, show a crossover from ferromagnetic to antiferromagnetic fluctuations on cooling and a freezing of dynamically fluctuating moments at low temperatures. We do not find any signatures of time-reversal symmetry breaking in stoichiometric LiFeAs that would support recent predictions of triplet pairing.