Low-temperature magnetic properties of amorphous germanium and silicon

The absolute magnetic susceptibility χ of amorphous Ge (a-Ge) prepared by evaporation, rf sputtering, and glow discharge decomposition of GeH₄ and of amorphous Si (a-Si) prepared by rf sputtering and glow discharge decomposition of SiH₄ was measured in the range of 1.5≤T≤300 K. The spin component χS of χ was fit to a Curie-Weiss law χS=C(T+ΘN) for $T>10$ K with ΘN between 0 and 4 K depending on the sample's state of anneal. Before annealing all samples except glow discharge a-Ge deviate from Curie-Weiss behavior below 8 K suggesting antiferromagnetic ordering of most of the spins. As the annealing temperature TA is increased above 50^∘{}C, the spin density NS in sputtered and evaporated a-Ge decreases and the antiferromagnetic ordering temperature TN is reduced to less than 1.5 K for TA≈200^∘{}C. The effect of hydrogen doping of sputtered a-Ge is to reduce TN 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.