Electronic structure and magnetism for FeSi$_{(1-x)}$Ge$_x$ from supercell calculations

TL;DR

This study uses supercell calculations to explore how substituting Ge for Si in FeSi affects its electronic structure and magnetism, revealing a transition from insulating to magnetic metallic states near x=0.25.

Contribution

It provides detailed computational insights into the electronic and magnetic transitions in FeSi$_{(1-x)}$Ge$_x$, highlighting the roles of disorder and volume changes.

Findings

Band gap closes for x ≥ 0.3 due to disorder and volume increase.

Ferromagnetism emerges near x=0.25 and strengthens with x.

Electronic specific heat behavior explained by exchange splitting.

Abstract

Recent studies of FeSi$_{(1-x)}$Ge$_x$, which found a transition from an insulating to a magnetic metallic state near $x$=0.25, have revived the discussion about the role of strong correlation in these systems. Here are spin polarized band calculations made for 64-atom supercells of FeSi$_{(1-x)}$Ge$_x$ for different $x$ and different volumes for large $x$. The results show that the small band gap in FeSi is closed for $x \geq 0.3$, because of both substitutional disorder and increased volume. Ferromagnetism appears near this composition and becomes enforced for increasing $x$. The $x$-dependence of the electronic specific heat can be understood from the exchange splitting of the density-of-states near the gap. Strong volume dependencies for the properties of FeGe suggest experiments using pressure instead of $x$ for investigations of the gap.