Probing the antiferromagnetic structure of (111)-oriented heterostructures using angle dependent x-ray absorption spectroscopy

(111)-oriented perovskite oxide heterostructures offer unique properties such as a buckled honeycomb structure resembling that of graphene with the stacking of highly polar layers. These factors impact the magnetic structure and exchange coupling in epitaxial heterostructures composed of ferromagnetic (FM) and antiferromagnetic (AF) layers. We demonstrate the development of measurement protocols for angle-dependent soft x-ray absorption spectroscopy measurements from (111)-oriented heterostructures which are used to unambiguously determine the orientation of the AF spin axis and how it responds to an applied magnetic field due to exchange coupling interactions with the adjacent FM layer. For the La_0.7Sr_0.3MnO₃/La_0.7Sr_0.3FeO₃ (LSFO) system, the LSFO layers possess two populations of AF order: the majority of AF moments cant out-of-the-plane of the film along low-index crystallographic directions, while a minority of AF moments lie within the (111)-plane. The relative orientation of the AF and FM spins differs for each type of AF domain. These results highlight the complexity of magnetic interactions which depend on factors such as crystalline orientation, sublayer thickness, and applied magnetic field which can be used to tune the AF order in perovskite oxide heterostructures.