Strain-induced atomic-scale building blocks for ferromagnetism in epitaxial LaCoO3

TL;DR

This study reveals that strain-induced ferromagnetism in LaCoO3 thin films originates from compressed structural units within twin-wall domains, not directly from strain, emphasizing the role of ferroelasticity in magnetic behavior.

Contribution

It uncovers the atomic-scale origin of strain-induced ferromagnetism in LaCoO3, linking it to ferroelastic twin-wall domains and high-spin/low-spin order, combining microscopy and theoretical calculations.

Findings

Ferromagnetism arises from compressed structural units in twin-wall domains.

Ferroelastic structural units exhibit high-spin/low-spin magnetic order.

Strain influences magnetic properties via structural domain formation.

Abstract

The origin of strain-induced ferromagnetism, which is robust regardless of the type and degree of strain in LaCoO3 (LCO) thin films, is enigmatic despite intensive research efforts over the past decade. Here, by combining scanning transmission electron microscopy with ab initio density functional theory plus U calculations, we report that the ferromagnetism does not emerge directly from the strain itself, but rather from the creation of compressed structural units within ferroelastically formed twin-wall domains. The compressed structural units are magnetically active with the rocksalt-type high-spin/low-spin order. Our study highlights that the ferroelastic nature of ferromagnetic structural units is important for understanding the intriguing ferromagnetic properties in LCO thin films.