Suppressed reflectivity due to spin-controlled localization in a magnetic semiconductor

TL;DR

This study reveals how spin polarization in Co-doped FeSi suppresses metallic reflectivity and increases charge carrier scattering, driven by disorder and electron interactions, leading to reduced metallicity even in fully polarized states.

Contribution

It uncovers a novel mechanism where spin polarization enhances disorder effects, reversing traditional interaction-disorder relationships in magnetic semiconductors.

Findings

Up to 25% reduction in mean-free path due to spin polarization.

Suppression of metallic reflectivity linked to increased scattering.

Deepening potential wells from Co atoms cause localization effects.

Abstract

The narrow gap semiconductor FeSi owes its strong paramagnetism to electron-correlation effects. Partial Co substitution for Fe produces a spin-polarized doped semiconductor. The spin-polarization causes suppression of the metallic reflectivity and increased scattering of charge carriers, in contrast to what happens in other magnetic semiconductors, where magnetic order reduces the scattering. The loss of metallicity continues progressively even into the fully polarized state, and entails as much as a 25% reduction in average mean-free path. We attribute the observed effect to a deepening of the potential wells presented by the randomly distributed Co atoms to the majority spin carriers. This mechanism inverts the sequence of steps for dealing with disorder and interactions from that in the classic Al'tshuler Aronov approach - where disorder amplifies the Coulomb interaction between carriers - in that here, the Coulomb interaction leads to spin polarization which in turn amplifies the disorder-induced scattering.