Colossal anomalous Hall conductivity and topological Hall effect in ferromagnetic kagome metal Nd3Al

We report a polycrystalline kagome metallic ferromagnet Nd3Al with a large unconventional positive magnetoresistance (similar to 80%) and a colossal anomalous Hall conductivity of 3 x 10(4) S/cm. We find that, though it is predominantly ferromagnetic, the low temperature phase is rather complex. The reduction in the effective moment, thermomagnetic irreversibility, anomalous temperature dependence of magnetization, large and non-saturating positive magnetoresistance, and existence of the finite topological Hall effect make this compound quite interesting. Various experimental proofs point toward topological band structure and topological spin texture in the frustrated kagome lattice. Ab initio calculations broadly confirm the presence of flatbands and Weyl points originating from the itinerant Nd-moments. The non-trivial band structure, enhanced skew scattering, and topological spin texture in a frustrated kagome lattice are found to be responsible for the colossal Hall conductivity and the topological Hall effect.