Two-channel anomalous Hall effect originating from the intermixing in Mn2CoAl/Pd thin films

The anomalous Hall effect (AHE) is an electronic transport phenomenon with rich physics. In thin magnetic films and multilayers, an unusual peak observed in AHE is often identified as the topological Hall effect (THE), induced by topologically nontrivial spin textures. However, it is a challenge to determine whether this unusual peak truly originates from such spin textures or is an artifact due to inhomogeneities. In this work, we systematically study the Pd thickness and temperature dependence of the Hall effect in ${\mathrm{Mn}}_{2}\mathrm{CoAl}$/Pd thin films. We observe an unusual peak in the Pd thickness dependence and rule out that the origin of the peak is from the topologically nontrivial spin textures by directly imaging the magnetic domain structures. We also build a model for the AHE based on the sum of contributions from ${\mathrm{Mn}}_{2}\mathrm{CoAl}$ and an intermixed CoPd alloy. These materials have opposite signs of the AHE and different coercive fields, which successfully explains the thickness and temperature behaviors of the unusual peak. Our results show that the interface mixing layer can play an important role in the interpretation of the AHE in ferromagnet/heavy metal systems.