Unusual Anomalous Hall Effect in a Co_2MnSi/MnGa/Pt Trilayer

An ultra-thin Co_2MnSi(0.5 nm)/MnGa(1.5 nm) bilayer capped with Pt (5 nm) has been successfully grown by molecular-beam epitaxy. It is a potential candidate of synthetic antiferromagnets due to antiferromagnetic coupling between Co_2MnSi and MnGa, which is a promising skyrmion-racetrack-memory medium without skyrmion Hall effect after capping with a Pt layer. Unusual humps in transverse Hall resistance loops are clearly observed in the temperature range from 260 to 400 K. This anomaly is generally attributed to topological Hall effect, but other than that, we prove that non-uniform rotation of magnetic moments in the bilayer with magnetic field sweeping is also a possible mechanism contributed to the unusual hump.