Origin of the Surface Magnetic Dead Layer in Rare‐Earth Titanates

Abstract

Perovskite rare‐earth titanates RTiO3 display a rich array of magnetic and electronic properties, with a Mott‐insulating ground state and ferro‐ or antiferromagnetic spin orders depending on the rare‐earth R. The nominal Ti valence is 3+ with a corresponding 3d1 configuration. Yet, at the surface of both bulk and thin films of RTiO3, the Ti valence has been found to strongly deviate towards the more stable 4+ state, adversely affecting magnetic properties. While this finding is rather ubiquitous, its exact origin is still poorly understood, which hampers the integration of RTiO3 into complex heterostructures harnessing their rich physics. Here, scanning transmission electron microscope and electron energy loss spectroscopy experiments are used to analyze the top part of an epitaxial DyTiO3 thin film displaying a well‐developed Ti4+‐rich layer over several nanometres. It shows that this valence evolution is related to a combination of short‐range ordered interstitial oxygen planes and Ti‐Dy cationic imbalance. Both defects synergistically contribute to enough hole doping for a complete transition toward Ti4+ over a few unit‐cells from the surface while a structure primarily of the perovskite‐type is maintained.