Characteristic temperature in magnetically doped amorphous semiconductors

Abstract

The introduction of magnetic moments such as Gd into amorphous Si produces dramatic effects in electrical transport below a characteristic temperature ${T}^{*}$. Below ${T}^{*}$, the conductivity of the magnetically doped systems is strongly suppressed compared to equivalent nonmagnetic Y doped samples, and displays enormous negative magnetoresistance. ${T}^{*}$ occurs at relatively high temperatures $(\ensuremath{\sim}10\char21{}100\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ and decreases sharply with increasing Gd concentration, passing smoothly through the metal-insulator transition. In ternary samples with both Gd and nonmagnetic Y, ${T}^{*}$ decreases strongly with increasing metallization, whether due to the addition of Gd alone or a mixture of Gd and Y. These results cannot be explained by simple magnetic interaction models, suggest the crucial role of electron screening and are reminiscent of mass enhancement behavior.