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This paper investigates the conditions for altermagnetism in rutile RuO2 by integrating experimental data with first-principles calculations, focusing on epitaxial strain, defects, doping, and interfaces. While bulk RuO2 appears nonmagnetic, thin films exhibit magnetic signatures dependent on structural context, with epitaxial strain identified as the primary driver for altermagnetism. The study predicts specific substrate-orientation combinations that stabilize this phase and elucidates how carrier doping and chemical substitution modulate the magnetic state.
Epitaxial strain, not intrinsic bulk properties, is the key to unlocking altermagnetism in RuO2 thin films, with specific substrate combinations predicted to stabilize the phase.
The magnetic ground state of rutile RuO2 remains disputed, raising a central question: under what structural and chemical conditions can this material support altermagnetism? We address this question by combining a critical assessment of experimental and theoretical studies with first-principles calculations of epitaxial strain, point defects, doping, and interfaces. Bulk-sensitive measurements reported in the literature are consistent with a nonmagnetic ground state, while magnetic signatures in thin films depend strongly on their structural environment and do not necessarily establish homogeneous altermagnetic order. Our calculations identify substrate-imposed epitaxial strain as the leading factor favoring altermagnetism among the conditions examined and predict several substrate-orientation combinations that stabilize an altermagnetic ground state. Carrier doping and chemical substitution modify this strain-induced magnetism in distinct ways. Uniform hole doping strengthens the magnetic tendency, whereas Ru vacancies provide little benefit and can weaken the magnetic state through local structural distortions. Cr or Mn substitution, by contrast, enhances Ru magnetic moments and further stabilizes the strained altermagnetic phase. These results distinguish the effects of carrier doping from those of local structural and chemical changes and identify concrete routes to realizing altermagnetism in RuO2 films.