Large anomalous Hall effect in a half-Heusler antiferromagnet

The anomalous Hall effect is usually associated with ferromagnets but a large anomalous Hall response can be found in topologically non-trivial half-Heusler antiferromagnets thanks to Berry phase effects associated with symmetry breaking. The quantum mechanical (Berry) phase of the electronic wavefunction plays a critical role in the anomalous 1 , 2 and spin Hall effects 3 , 4 , including their quantized limits 5 , 6 , 7 . While progress has been made in understanding these effects in ferromagnets 8 , less is known in antiferromagnetic systems. Here we present a study of antiferromagnet GdPtBi, whose electronic structure is similar to that of the topologically non-trivial HgTe (refs 9 , 10 , 11 ), and where the Gd ions offer the possibility to tune the Berry phase via control of the spin texture. We show that this system supports an anomalous Hall angle Θ AH > 0.1, comparable to the largest observed in bulk ferromagnets 12 and significantly larger than in other antiferromagnets 13 . Neutron scattering measurements and electronic structure calculations suggest that this effect originates from avoided crossing or Weyl points that develop near the Fermi level due to a breaking of combined time-reversal and lattice symmetries. Berry phase effects associated with such symmetry breaking have recently been explored in kagome networks 14 , 15 , 16 , 17 ; our results extend this to half-Heusler systems with non-trivial band topology. The magnetic textures indicated here may also provide pathways towards realizing the topological insulating and semimetallic states 9 , 10 , 11 , 18 , 19 predicted in this material class.