Surface-Localized Magnetic Order in RuO2 Thin Films Revealed by Low-EnergyMuon Probes

Ruthenium dioxide (RuO2) has recently emerged as a altermagnetic candidate, but its intrinsic magnetic ground state in thin films remains widely debated. This study aims to clarify the nature and spatial extent of the magnetic order in RuO2 thin films grown under different conditions. Thin films of RuO2 with thicknesses of 30 nm and 33 nm are deposited by pulsed laser deposition and sputtering onto TiO2(110) and Al2O3( ¯1102) substrates, respectively. Low-energy muon spin rotation/relaxation (LE-μSR) with depth-resolved sensitivity measurements are performed in transverse magnetic fields (TF) from 4 K to 290 K. The μSR data collected with muon implantation energy of 1 keV reveal that magnetic signals originate from the near-surface region of the film (