# Structural, Electronic and Magnetic Properties of Bulk and Epitaxial LaCoO$_3$ through Diffusion Monte Carlo

## TL;DR

This study uses advanced computational methods to explore the magnetic, electronic, and structural properties of LaCoO$_3$, revealing new insights into its ferromagnetism driven by strain and defects, with implications for material design.

## Contribution

The paper applies diffusion Monte Carlo calculations to elucidate the magnetic states of LaCoO$_3$, showing ferromagnetism can be induced by strain and defects, contrasting previous assumptions about its nonmagnetic bulk form.

## Key findings

- Bulk LaCoO$_3$ is antiferromagnetic in the ground state.
- Ferromagnetism in epitaxial LaCoO$_3$ can be promoted by strain and superstructure modulation.
- Defects and strain significantly influence magnetic properties.

## Abstract

Magnetism in lanthanum cobaltite (LCO, LaCoO$_3$) appears to be strongly dependent on strain, defects, and nanostructuring. LCO on strontium titanate (STO, SrTiO$_3$) is a ferromagnet with an interesting strain relaxation mechanism that yields a lattice modulation. However, the driving force of the ferromagnetism is still controversial. Experiments debate between a vacancy-driven or strain-driven mechanism for the ferromagnetism of epitaxial LCO. We found that a weak lateral modulation of the superstructure is sufficient to promote ferromagnetism. We find that ferromagnetism appears under uniaxial compression and expansion. Although earlier experiments suggest that bulk LCO is nonmagnetic, we find an antiferromagnetic ground state for bulk LCO. We discuss the recent experiments which indicate a more complicated picture for bulk magnetism and a closer agreement with our calculations. Role of defects are also discussed through excited state calculations.