Magnetism in Na-filled Fe-based skutterudites

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. NaFe(4)Sb(12) 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. NaFe(4)P(12) also shows a ferromagnetic instability at the density functional level, but this instability is much weaker than that of NaFe(4)Sb(12), possibly placing it on the paramagnetic side of the quantum critical point. NaFe(4)As(12) shows intermediate behavior. We also present results for skutterudite FeSb(3), which is a metastable phase that has been reported in thin film form.