Imaging and Control of Ferromagnetism in a Polar Antiferromagnet

TL;DR

This study demonstrates an atomically sharp phase transition from antiferromagnetic to ferromagnetic in ultrathin LaMnO3 films on SrTiO3, driven by electronic reconstruction due to polarity effects, revealing new emergent functionalities at the atomic scale.

Contribution

It reports the first direct visualization and control of a magnetic phase transition in atomically thin polar oxide films, highlighting the role of electronic reconstruction.

Findings

Antiferromagnetic to ferromagnetic transition at six unit cells thickness

Visualization of the phase transition using scanning SQUID microscopy

Electronic reconstruction explains the phase change

Abstract

Atomically sharp oxide heterostructures often exhibit unusual physical properties that are absent in the constituent bulk materials. The interplay between electrostatic boundary conditions, strain and dimensionality in ultrathin epitaxial films can result in monolayer-scale transitions in electronic or magnetic properties. Here we report an atomically sharp antiferromagnetic-to-ferromagnetic phase transition when atomically growing polar antiferromagnetic LaMnO3 (001) films on SrTiO3 substrates. For a thickness of five unit cells or less, the films are antiferromagnetic, but for six unit cells or more, the LaMnO3 film undergoes a phase transition to a ferromagnetic state over its entire area, which is visualized by scanning superconducting quantum interference device microscopy. The transition is explained in terms of electronic reconstruction originating from the polar nature of the LaMnO3 (001) films. Our results demonstrate how new emergent functionalities can be visualized and engineered in atomically thick oxide films at the atomic level.