Interfacial Modulation on Co_0.2Fe_2.8O₄ Epitaxial Thin Films for Anomalous Hall Sensor Applications

Magnetic oxide films with a strong anomalous Hall effect (AHE) have attracted much attention due to their strong sensitivity and high polarization for magnetic sensor applications. However, the linearity of the anomalous Hall sensors still needs improving. In this work, we propose to use the interface regulation to improve the linearity of the AHE. We grow spinel ferrite Co_0.2Fe_2.8O₄ (CoFeO) thin films on MgAl₂O₄ (MAO) substrates and alter their interfacial properties by inserting a graphene layer between the MAO substrate and the CoFeO film. Through a detailed structure and performance analysis, it reveals that the insertion of graphene has not broken the epitaxial nature of the films but endows the film with a nanopillar-like structure. A series of electrical tests show that the Hall resistance signal of our thin film system has high sensitivity and high linearity to the magnetic field. Reduced hysteresis and better linearity of the anomalous Hall resistance were found in the graphene-inserted heterostructure due to differences in the nanostructure and possibly interfacial coupling. These results suggest that interfacial engineering offers a pathway to tune the performance of ferrite thin film systems for sensor applications.