Effects of altermagnetic order, strain and doping in RuO$_2$

TL;DR

This study combines experimental measurements and first-principles calculations to investigate how altermagnetic order, strain, and doping influence the optical and vibrational properties of RuO$_2$, revealing a complex interplay of magnetic states.

Contribution

It provides new insights into the magnetic states of RuO$_2$ under various strain conditions, combining experimental data with theoretical analysis.

Findings

RuO$_2$ exhibits a nonmagnetic ground state in bulk.

Strain on TiO$_2$ (001) does not induce magnetism.

Strain on TiO$_2$ (110) stabilizes nearly degenerate ferromagnetic and altermagnetic states.

Abstract

RuO$_2$, one of the most widely studied transition metal oxides, was recently predicted to host a novel form of collinear magnetic order referred to as altermagnetism. In this study we combine experiment (reflectance, transmittance, ellipsometry and Raman measurements) and first-principles calculations to elucidate the potential role of altermagnetic order, strain and doping on the optical and vibrational properties of RuO$_2$ grown on TiO$_2$ (001), (101) and (110) substrates. Our combined experimental and theoretical results point toward a nonmagnetic ground state as the most consistent description of the optical and vibrational properties of bulk RuO$_2$. RuO$_2$ strained to TiO$_2$ (001) remains nonmagnetic in our calculations. Straining to TiO$_2$ (110) stabilizes ferromagnetic and altermagnetic states that are nearly degenerate and both lower in energy than the nonmagnetic state. The relative energetic ordering of these states is highly sensitive to the level of strain and the choice of exchange-correlation approximation.