Quenched magnetic moment in Mn-doped amorphous Si (\textit{a}-Mn$_{x}$Si$_{1-x}$) across the metal-insulator transition

TL;DR

This study investigates the magnetic and electrical properties of Mn-doped amorphous silicon films, revealing quenched magnetic moments and a small positive magnetoresistance, contrasting with crystalline silicon behavior.

Contribution

It uncovers that most Mn atoms in amorphous silicon do not contribute to magnetization, challenging existing models and explaining the small magnetoresistance observed.

Findings

Most Mn atoms are magnetically inactive in amorphous silicon.

Only interstitial Mn$^{2+}$ states contribute to magnetization.

The films exhibit small positive magnetoresistance.

Abstract

The magnetic and electrical transport properties of Mn-doped amorphous silicon (\textit{a-}Mn$_{x}$Si$_{1-x}$) thin films have been measured. The magnetic susceptibility obeys the Curie-Weiss law for a wide range of $x$ (0.005-0.175) and the saturation moment is small. While all Mn atoms contribute to the electrical transport, only a small fraction (interstitial Mn$^{2+}$ states with $J$=$S$=5/2) contribute to the magnetization. The majority of the Mn atoms do not possess any magnetic moment, contrary to what is predicted by the Ludwig-Woodbury model for Mn in crystalline silicon. Unlike \textit{a-}Gd$_{x}$Si$_{1-x}$ films which have an enormous \textit{negative} magnetoresistance, \textit{a-}Mn$_{x}$Si$_{1-x}$ films have only a small \textit{positive} magnetoresistance, which can be understood by this quenching of the Mn moment.