Concentration dependence of magnetic and transport properties of amorphous Gd-Ge alloys

The properties of Gd
100-x
Ge
x
amorphous alloys show an unusual dependence on composition. At x = 50% the saturation magnetization and Curie temperature decrease precipitously. The resistivity and spontaneous Hall effect also have complex behavior in the same composition region. There is a maximum in ρ at 43% Ge superimposed on a more monotonic increase with increasing x. Also at x = 43% there is a pronounced maximum in the tangent of the Hall angle, ρ
H
/ρ. In addition to the peak at 43%, the resistivity also increases steeply above 75% Ge extrapolating toward values found for semiconducting, amorphous germanium. The Hall conductivity (ρ
H
/ρ
²
), on the other hand, decreases monotonically with increasing x over the entire composition range, x = 20 to 82%. In general, the spontaneous Hall effect in this metal-semiconductor system can be understood in terms of the Berger "side jump" model.