Altermagnets, a recently discovered class of magnetic materials exhibiting ferromagneticlike spin-split bands and antiferromagneticlike compensated magnetic order, have attracted significant interest for next-generation spintronic applications. Ruthenium dioxide (${\mathrm{Ru}\mathrm{O}}_2$) has emerged as a promising altermagnetic candidate due to its compensated antiparallel magnetic order and strong spin-split electronic bands. However, recent experimental and theoretical reports also suggest that ${\mathrm{Ru}\mathrm{O}}_2$ may be nonmagnetic in its ground state, underscoring the need for deeper investigations into its magnetic character. Specifically, (100)-oriented ${\mathrm{Ru}\mathrm{O}}_2$ films are expected to generate spin currents with transverse spin polarization parallel to the Néel vector. Here, we investigate magnetotransport in epitaxial ${\mathrm{Ru}\mathrm{O}}_2/$permalloy (Py) heterostructures to examine spin Hall magnetoresistance and interfacial effects generated in such systems. Our measurements reveal a pronounced negative angular-dependent magnetoresistance for variation of magnetic field direction perpendicular to the charge current direction. Detailed measurements dependent on temperature, magnetic field, and crystallographic orientation indicate that interface-generated spin current (IGSC) at the ${\mathrm{Ru}\mathrm{O}}_2/$Py interface predominantly governs the observed magnetoresistance. In addition, the role of the IGSC contribution to the observed magnetoresistance was demonstrated through drift-diffusion calculations. This shows that strong interface effects predominate over possible altermagnetic contributions from ${\mathrm{Ru}\mathrm{O}}_2$. Our results show that the role of IGSCs is crucial and should not be overlooked in studies of altermagnetic systems. A critical step in this direction is disentangling interfacial from altermagnetic contributions. The insight into interfacial contributions from altermagnetic influences is essential for the advancement of ${\mathrm{Ru}\mathrm{O}}_2$-based spintronic memory and sensing applications.

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• Magnetoresistance
• Spin current
• Surface & interfacial phenomena
• Altermagnets
• Ferromagnets
• Magnetic thin films
• Transition metal alloys
• Transition metal oxides