Strain Engineering of Altermagnetic Symmetry in Epitaxial RuO$_2$ Films

TL;DR

This study demonstrates how compressive strain induces altermagnetic phases in RuO₂ thin films, with experimental and theoretical evidence showing tunable magnetic properties and symmetry-dependent magnetic orders.

Contribution

It reveals strain-induced altermagnetism in RuO₂ films through combined first-principles calculations and experimental validation, highlighting symmetry effects and tunability.

Findings

Compressive strain stabilizes altermagnetic phase in RuO₂.

Strain enhances density of states near Fermi level, causing Fermi surface instability.

(100) RuO₂ exhibits ideal altermagnetic order, while (110) shows ferrimagnetic state.

Abstract

The magnetic ground state of RuO$_2$ has been under intense debate. Using first-principles calculations, we show that compressive strain along [001] direction stabilizes an altermagnetic phase in RuO$_2$ thin films grown on (100) and (110) TiO$_2$ substrates. We further identify that compressive strain enhances the density of states near the Fermi level, resulting in a Fermi surface instability and the emergence of altermagnetism. The magnitude of strain and the associated increase in the density of states can be tuned by varying the film thickness, as systematically confirmed by x-ray diffraction and photoemission spectroscopy measurements. Symmetry analysis further reveals that (100) RuO$_2$ hosts an ideal altermagnetic order, whereas broken symmetry in (110) films leads to an uncompensated ferrimagnetic state. Finally, we discuss the effects of Hubbard $U$ parameters and evaluate the realistic tunneling magnetoresistance of (100) RuO$_2$.