Coupling of Anomalous Hall and Planar Hall Effects in Ferromagnet/Antiferromagnet Bilayers

The Hall effect in ferromagnetic (FM) materials is typically linked to magnetization, yet its manifestation in complex heterostructures remains poorly understood. Here, we demonstrate that antiferromagnetic (AFM) NiO can modulate the ferromagnetic state of epitaxial SrRuO₃ (SRO). We systematically investigate the structural, magnetic, and transport properties of SRO/NiO, NiO/SRO, and single-layer SRO films. Remarkably, only the SRO/NiO bilayer exhibits a pronounced unconventional hump-dip feature in the Hall hysteresis, which is absent in NiO/SRO and pure SRO. Microstructural analysis reveals the presence of nanosized globular NiO in the SRO/NiO bilayer, which increases the interfacial area and promotes spin misalignment and modifies magnetic anisotropy of SRO. This spin disorder and modified anisotropy strongly alter the magnetic and transport responses in the SRO/NiO heterostructure. We attribute the irregular Hall feature to a temperature-dependent interplay of the anomalous Hall effect (AHE), planar Hall effect (PHE), and magnetoresistance in the SRO/NiO heterostructure. These findings highlight the critical role of the AFM/FM interfacial microstructure in tailoring Hall transport phenomena.