Strain-Induced Atomic-Scale Building Blocks for Ferromagnetism in Epitaxial LaCoO₃.

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 <i>ab initio</i> density functional theory <i>plus U</i> 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.