Magnetism in Na-filled Fe-based skutterudites

TL;DR

This study uses first principles calculations to explore magnetism in Na-filled Fe-based skutterudites, revealing different magnetic behaviors near quantum critical points and providing insights into their magnetic states.

Contribution

It provides the first computational analysis of magnetism in Na-filled Fe-based skutterudites, highlighting their proximity to quantum criticality and differences in magnetic tendencies.

Findings

NaFe4Sb12 is a ferromagnetic metal near a quantum critical point.

NaFe4P12 shows a weaker ferromagnetic instability, possibly paramagnetic.

NaFe4As12 exhibits intermediate magnetic behavior.

Abstract

The interplay of superconductivity and magnetism is a subject of ongoing interest, stimulated most recently by the discovery of Fe-based superconductivity and the recognition that spin-fluctuations near a magnetic quantum critical point may provide an explanation for the superconductivity and the order parameter. Here we investigate magnetism in the Na filled Fe-based skutterudites using first principles calculations. NaFe4Sb12 is a known ferromagnet near a quantum critical point. We find a ferromagnetic metallic state for this compound driven by a Stoner type instability, consistent with prior work. In accord with prior work, the magnetization is overestimated, as expected for a material near an itinerant ferromagnetic quantum critical point. NaFe4P12 also shows a ferromagnetic instability at the density functional level, but this instability is much weaker than that of NaFe4Sb12, possibly placing it on the paramagnetic side of the quantum critical point. NaFe4As12 shows intermediate behavior. We also present results for skutterudite FeSb3, which is a metastable phase that has been reported in thin film form.