Electron Accumulation and Emergent Magnetism in LaMnO3/SrTiO3 Heterostructures

TL;DR

This study investigates how electron accumulation and ferromagnetism emerge at LaMnO3/SrTiO3 interfaces, revealing critical thicknesses for electron reconstruction and magnetic order, and demonstrating control over these phenomena through doping.

Contribution

It uncovers the distinct critical thicknesses for electron accumulation and ferromagnetism, and shows how doping can manipulate emergent magnetic properties at ultrathin oxide interfaces.

Findings

Electron accumulation occurs at 2 unit cells.

Ferromagnetism emerges at 5 unit cells.

Doping enables ferromagnetism in 3-unit-cell films.

Abstract

Emergent phenomena at polar-nonpolar oxide interfaces have been studied intensely in pursuit of next-generation oxide electronics and spintronics. Here we report the disentanglement of critical thicknesses for electron reconstruction and the emergence of ferromagnetism in polar-mismatched LaMnO3/SrTiO3 (001) heterostructures. Using a combination of element-specific X-ray absorption spectroscopy and dichroism, and first-principles calculations, interfacial electron accumulation and ferromagnetism have been observed within the polar, antiferromagnetic insulator LaMnO3. Our results show that the critical thickness for the onset of electron accumulation is as thin as 2 unit cells (UC), significantly thinner than the observed critical thickness for ferromagnetism of 5 UC. The absence of ferromagnetism below 5 UC is likely induced by electron over-accumulation. In turn, by controlling the doping of the LaMnO3, we are able to neutralize the excessive electrons from the polar mismatch in ultrathin LaMnO3 films and thus enable ferromagnetism in films as thin as 3 UC, extending the limits of our ability to synthesize and tailor emergent phenomena at interfaces and demonstrating manipulation of the electronic and magnetic structures of materials at the shortest length scales.