Hidden spin liquid in an antiferromagnet: Applications to FeCrAs

TL;DR

This paper proposes a theoretical model for FeCrAs, revealing a hidden spin liquid phase in the non-magnetic Fe sublattice that coexists with magnetic order in the Cr sublattice, explaining its unusual metallic and non-metallic properties.

Contribution

It introduces a microscopic Hamiltonian and uses slave-rotor mean field theory to identify a stable spin liquid phase in FeCrAs's Fe sublattice, a novel insight into its complex behavior.

Findings

Discovery of a spin liquid phase in the Fe sublattice.

Explanation of FeCrAs's metallic and non-metallic signatures.

Proximity to a metal-insulator transition influences properties.

Abstract

The recently studied material FeCrAs exhibits a surprising combination of experimental signatures, with metallic, Fermi liquid like specific heat but resistivity showing strong non-metallic character. The Cr sublattice posseses local magnetic moments, in the form of stacked (distorted) Kagome lattices. Despite the high degree of magnetic frustration, anti-ferromagnetic order develops below ~125K suggesting the non-magnetic Fe sublattice may play a role in stabilizing the ordering. From the material properties we propose a microscopic Hamiltonian for the low energy degrees of freedom, including the non-magnetic Fe sublattice, and study its properties using slave-rotor mean field theory. Using this approach we find a spin liquid phase on the Fe sublattice, which survives even in the presence of the magnetic Cr sublattice. Finally, we suggest that the features of FeCrAs can be qualitatively explained by critical fluctuations in the non-magnetic sublattice Fe due to proximity to a metal-insulator transition.