Origin of large moments in Mn$_x$Si$_{1-x}$ at small x

TL;DR

This paper explains the large magnetic moments in Mn-doped silicon at very low concentrations by identifying a specific atomic configuration that weakens hybridization, providing insights for tuning magnetic properties in semiconductors.

Contribution

The study reveals that a particular atomic arrangement involving second-neighbor interstitial Si causes large magnetic moments in Mn$_x$Si$_{1-x}$, a novel insight into magnetic behavior at low doping levels.

Findings

Large magnetic moments arise from specific atomic configurations.

Weakened d-p hybridization explains the large moments.

A 513-atom model reproduces the observed magnetic moment.

Abstract

Recently, the magnetic moment/Mn, $M$, in Mn$_x$Si$_{1-x}$ was measured to be 5.0 $\mu_B$/Mn, at $x$ =0.1%. To understand this observed $M$, we investigate several Mn$_x$Si$_{1-x}$ models of alloys using first-principles density functional methods. The only model giving $M = 5.0$ was a 513-atom cell having the Mn at a substitutional site, and Si at a second-neighbor interstitial site. The observed large moment is a consequence of the weakened d-p hybridization between the Mn and one of its nearest neighbor Si atoms, resulting from the introduction of the second-neighbor interstitial Si. Our result suggests a way to tune the magnetic moments of transition metal doped semiconductors.