  The coupling of electron spin to real-space magnetic textures leads to a
variety of interesting magnetotransport effects. The skyrmionic spin textures
often found in chiral B20-lattice magnets give rise, via real-space Berry
phases, to the topological Hall effect, but it is typically rather small. Here,
B20-ordered Fe$_{0.7}$Co$_{0.3}$Si epilayers display a giant topological Hall
effect due to the combination of three favourable properties: they have a high
spin-polarisation, a large ordinary Hall coefficient, and dense chiral spin
textures. The topological Hall resistivity is as large as 820 n$\Omega$cm at
helium temperatures. Moreover, we observed a drop in the longitudinal
resistivity of 100 n$\Omega$cm at low temperatures in the same field range,
suggesting that it is also of topological origin. That such strong effects can
be found in material grown in thin film form on commercial silicon wafer bodes
well for skyrmion-based spintronics.
