Low-temperature magnetic properties of amorphous germanium and silicon

Abstract

The absolute magnetic susceptibility $\chi$ of amorphous $\mathrm{Ge} (a-\mathrm{Ge})$ prepared by evaporation, rf sputtering, and glow discharge decomposition of Ge${\mathrm{H}}_4$ and of amorphous $\mathrm{Si} (a-\mathrm{Si})$ prepared by rf sputtering and glow discharge decomposition of Si${\mathrm{H}}_4$ was measured in the range of $1.5\le T\le 300$ K. The spin component ${\chi }_S$ of $\chi$ was fit to a Curie-Weiss law ${\chi }_S=\frac{C}{(T+{\Theta }_N)}$ for $T>\mathrm{}10\mathrm{}$ K with ${\Theta }_N$ between 0 and 4 K depending on the sample's state of anneal. Before annealing all samples except glow discharge $a-\mathrm{Ge}$ deviate from Curie-Weiss behavior below 8 K suggesting antiferromagnetic ordering of most of the spins. As the annealing temperature $T_A$ is increased above 50°C, the spin density $N_S$ in sputtered and evaporated $a-\mathrm{Ge}$ decreases and the antiferromagnetic ordering temperature $T_N$ is reduced to less than 1.5 K for $T_A\approx 200$°C. The effect of hydrogen doping of sputtered $a-\mathrm{Ge}$ is to reduce $T_N$ below 1.5 K. These results are discussed in terms of several theories of amorphous antiferromagnetism and the present understanding of spins in amorphous tetrahedral semiconductors.