# Magnetic ground state of SrRuO$_3$ thin film and applicability of standard first-principles approximations to metallic magnetism

## TL;DR

This study systematically compares LDA and GGA approximations in predicting the magnetic ground state of SrRuO$_3$ thin films, revealing significant differences especially under strain, and discusses their applicability to metallic magnetic systems.

## Contribution

It provides a detailed first-principles analysis of SrRuO$_3$ thin films, highlighting the limitations of standard approximations in metallic magnetism predictions.

## Key findings

- LDA and GGA give different predictions for thin film magnetism under strain.
- Both approximations agree for bulk SrRuO$_3$, but diverge in thin film conditions.
- Standard methods may have limitations in modeling correlated oxide and metallic magnetic systems.

## Abstract

A systematic first-principles study has been performed to understand the magnetism of thin film SrRuO$_3$ which lots of research efforts have been devoted to but no clear consensus has been reached about its ground state properties. The relative t$_{2g}$ level difference, lattice distortion as well as the layer thickness play together in determining the spin order. In particular, it is important to understand the difference between two standard approximations, namely LDA and GGA, in describing this metallic magnetism. Landau free energy analysis and the magnetization-energy-ratio plot clearly show the different tendency of favoring the magnetic moment formation, and it is magnified when applied to the thin film limit where the experimental information is severely limited. As a result, LDA gives a qualitatively different prediction from GGA in the experimentally relevant region of strain whereas both approximations give reasonable results for the bulk phase. We discuss the origin of this difference and the applicability of standard methods to the correlated oxide and the metallic magnetic systems.