Emergent c -axis magnetic helix in manganite-nickelate superlattices

The nature of the magnetic order in (La2/3Sr1/3MnO3)9/(LaNiO3)3 superlattices is investigated using x-ray resonant magnetic reflectometry. We observe a c-axis magnetic helix state in the (LaNiO3)3 layers that has not been reported in bulk nickelates, and which mediates the ∼130∘ magnetic coupling between the ferromagnetic (La2/3Sr1/3MnO3)9 layers, illustrating the power of x rays for discovering the magnetic state of complex oxide interfaces. Resonant inelastic x-ray scattering and x-ray absorption spectroscopy show that Ni-O ligand hole states from bulk LaNiO3 are mostly filled due to an interfacial electron transfer from Mn, driving the Ni orbitals closer to an atomiclike 3d8 configuration. We discuss the constraints imposed by this electronic configuration to the microscopic origin of the observed magnetic structure. The presence of a magnetic helix in (La2/3Sr1/3MnO3)9/(LaNiO3)3 is crucial for modeling the potential spintronic functionality of this system and may be important for designing emergent magnetism in novel devices in general.