Magnetic coupling in La_2/3Sr_1/3MnO₃/SrRuO₃ heterostructures grown on SrTiO₃ (111) substrates with abrupt interface

We report on the magnetic coupling behavior in all-ferromagnetic La_0.7Sr_0.3MnO₃/SrRuO₃ (LSMO/SRO) heterostructures deposited on the SrTiO₃ (111) substrate, where the interface leads to an enhanced exchange field as compared to the one deposited on SrTiO₃ (001). Importantly, high-resolution scanning transmission electron microscopy reveals distinct interface structures of the (111) heterostructures depending on the growth sequence. The heterostructure with an SRO bottom layer shows an atomically flat and abrupt interface, while the one with an LSMO bottom layer shows a deformed interface due to the surface roughening of LSMO deposited directly on SrTiO₃ (111). As a result, the heterostructure with an abrupt interface exhibits a robust antiferromagnetic coupling between LSMO and SRO, while the one with a rough interface shows negligible magnetic coupling. Our results demonstrate the key role of an abrupt interface in determining the magnetic properties of oxide heterostructures.