Controlling magnetic properties of LaMnO₃/SrTiO₃ heterostructures by electronic reconstruction and stoichiometry: atomic scale evidence

Interface driven magnetic effects and phenomena associated with spin-orbital coupling and intrinsic symmetry breaking are of importance for fundamental physics and device applications. How interfaces affect the interplay between charge, spin, orbital and lattice degrees of freedom is the key to boost the device performances. In LaMnO₃ (LMO)/SrTiO₃ polar-nonpolar heterostructures, electronic reconstruction leads to an antiferromagnetic to ferromagnetic transition, making them viable for spin filter applications. The detailed electronic structure across the interfaces plays a critical role in understanding the microscopic origins of the observed magnetic phase transition, from antiferromagnetic at 5 unit cells (ucs) of LMO or below to ferromagnetic at 6 ucs or above. Here, we offer an atomic resolution picture of electronic reconstruction by quantifying the charge distribution across this abrupt magnetic transition using STEM-EELS. We find that the electronic reconstruction is confined within the first 2 ucs of LMO from the interface, and more importantly, it is robust against oxygen non-stoichiometry. When restoring stoichiometry, we achieve a ferromagnetic insulating state in LMO films with a thickness as thin as 2 nm, making LMO readily applicable as barriers in spin filters.