Direct experimental evidence of tunable charge transfer at the $LaNi{O}_3/CaMn{O}_3$ ferromagnetic interface

Abstract

Interfacial charge transfer in oxide heterostructures gives rise to a rich variety of electronic and magnetic phenomena. Designing heterostructures where one of the thin-film components exhibits a metal-insulator transition opens a promising avenue for controlling such phenomena both statically and dynamically. In this letter, we utilize a combination of depth-resolved soft X-ray standing-wave and hard X-ray photoelectron spectroscopies in conjunction with polarization-dependent X-ray absorption spectroscopy to investigate the effects of the metal-insulator transition in $LaNi{O}_3$ on the electronic and magnetic states at the $LaNi{O}_3/CaMn{O}_3$ interface. We report on a direct observation of the reduced effective valence state of the interfacial Mn cations in the metallic superlattice with an above-critical $LaNi{O}_3$ thickness (6 u.c.) due to the leakage of itinerant Ni 3d $e_g$ electrons into the interfacial $CaMn{O}_3$ layer. Conversely, in an insulating superlattice with a below-critical $LaNi{O}_3$ thickness of 2 u.c., a homogeneous effective valence state of Mn is observed throughout the $CaMn{O}_3$ layers due to the blockage of charge transfer across the interface. The ability to switch and tune interfacial charge transfer enables precise control of the emergent ferromagnetic state at the $LaNi{O}_3/CaMn{O}_3$ interface and, thus, has far-reaching consequences on the future strategies for the design of next-generation spintronic devices.