Observation of giant anomalous Hall effect in a topological magnet*

The boom of topological materials and the novel properties which they host has generated great interest in the condensed mattered community over the last decade.  An interesting research direction is coupling topological properties with strong correlations, electronic or magnetic, to design technologically useful materials. One such possibility is inducing magnetism in a Dirac semimetal, resulting in a net Berry curvature and thus a large anomalous Hall effect (AHE) response which has been proposed as a path towards energy efficient electronic and spintronic devices. Several compounds in the tetragonal BaAl₄ family (space group I4/mmm), possess Dirac cones near the Fermi level, which can be tuned by chemical substitution.  Furthermore, magnetism can be induced by substituting Ba with rare earth ions, providing a promising route to engineering a large AHE.

Here we report the observation of giant AHE in a Eu-based BaAl₄ -type compound. Indeed doping on the non-magnetic sublattice tunes the Dirac point to the Fermi level as probed by angle-resolved photoemission measurements. Our magneto-electrical transport measurements show that the onset of the AHE coincides with magnetic order below 20 K,  and monotonously increases on cooling. The anomalous Hall conductivity approaches 50x10³ (Ohm cm)^-1 and the tangent of the Hall angle is close to 0.14 at the lowest measured temperature of 2 K. We discuss possible origins of both the giant AHE and temperature dependence.