Along with the progression of the low-dimensional materials, the high-quality thin film and two-dimensional material come into the stage of spintronics, where the surfaces should be important or even dominate the transport phenomena. For anomalous Hall effect (AHE), however, the surfaces are mainly treated as an additional scattering source to the residual resistance, and the corresponding AHE is submerged by the bulk contributions. In this work, we have disentangled contributions from the surface and the bulk to the AHE in ${\mathrm{CoNi}}_3$ (001) epitaxial and ${\mathrm{CoNi}}_3$ polycrystalline films by varying thickness and temperature. The surface and the bulk anomalous Hall angles are found to have opposite signs for all temperatures and the corresponding surface anomalous Hall angles are surprisingly much larger than the bulk anomalous Hall angles. Furthermore, the first-principles calculations are carried out and the observed surface AHE is successfully replicated.

• Received 15 November 2023
• Revised 29 February 2024
• Accepted 1 March 2024

DOI:https://doi.org/10.1103/PhysRevB.109.104422