Quenched magnetic moment in Mn-doped amorphous Si films

Abstract

The absence of a Mn local moment was observed in Mn-doped amorphous silicon $(a\text{\ensuremath{-}}{\mathrm{Mn}}_{x}{\mathrm{Si}}_{1\ensuremath{-}x})$ films. The magnetic susceptibility obeys the Curie-Weiss law for a wide range of $x$ ($5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$ up to 0.175) but with extremely small moment. Magnetization measurements suggest that this behavior occurs because only a small percentage of Mn (${\mathrm{Mn}}^{2+}$ states with $J=S=5∕2$) contribute to the magnetization. Thus, the magnetic moments are quenched for the majority of Mn atoms, contrary to the general belief of the existence of a localized Mn moment in Si. X-ray absorption spectroscopy suggests that the quenching of Mn moments is attributed to the formation of an itinerant but Anderson-localized impurity band, forming at $x$ as low as $5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$.