  We report about the anomalous Hall effect in 4f 3d metallic alloys measured
using terahertz time-domain spectroscopy. The strength of the observed
terahertz spin-dependent transport phenomenon is in good agreement with
expectations based on electronic transport measurements. Employing this effect,
we succeeded to reveal ultrafast dynamics of the anomalous Hall effect which
accompanies the sub-100 picosecond optically induced magnetization reversal in
a GdFeCo alloy. The experiments demonstrate the ability to control currents at
terahertz frequencies in spintronic devices magnetically and ultrafast.
