  Historically, the genesis of anomalous Hall effect (AHE) in magnetic
materials has always been a fascinating yet controversial topic in the solid
state physics community. Recent progress on the understanding of this topic has
revealed an intimate connection between the Berry curvature of occupied
electronic states and the intrinsic AHE. Magnetic Weyl semimetals with broken
time reversal symmetry is a classic example, which is expected to show large
contributions to Berry curvature around the topological nodes and hence to the
AHE. Here, we report a kagome metallic ferromagnet Nd$_3$Al, with a large
unconventional positive magnetoresistance (~ 80 %) and colossal anomalous Hall
conductivity of 1.8x10^5 S/cm (largest ever reported to the best of our
knowledge). We also show that the magnetic state of this compound is quite
different from its analogues in many respects. While the compound is
predominantly an itinerant ferromagnet, its low temperature phase exhibits
topological band structure, enhanced skew scattering as well as topological
spin texture arising in the spin frustrated kagome lattice. Various
experimental findings such as topological Hall effect, non-saturating positive
magnetoresistance etc. give strong indication to this scenario. Ab-initio
calculations broadly confirm the experimental findings by revealing the
presence of flat bands and Weyl points originating from the itinerant Nd
moments. The non-trivial band structure, enhanced skew scattering and the spin
texture in a clean polycrystalline sample are found be responsible for the
colossal Hall conductivity and topological Hall effect.
