Angle-Dependent Magnetoresistance Induced by Interface-Generated Spin Current in RuO_2/Permalloy Heterostructures

Altermagnets, a recently discovered class of magnetic materials exhibiting ferromagnetic-likespin-split bands and antiferromagnetic-like compensated magnetic order, have attracted signifi-cant interest for next-generation spintronic applications. Ruthenium dioxide (RuO2) has emergedas a promising altermagnetic candidate due to its compensated antiparallel magnetic order andstrong spin-split electronic bands. However, recent experimental and theoretical reports also sug-gest that RuO2 may be non-magnetic in its ground state, underscoring the need for deeper in-vestigations into its magnetic character. Specifically, the (100)-oriented RuO2 films are expectedto generate spin currents with transverse spin polarization parallel to the N´eel vector. Here, weinvestigate magnetotransport in epitaxial RuO2/Permalloy (Py) heterostructures to examine spinHall magnetoresistance and interfacial effects generated in such systems. Our measurements re-veal a pronounced negative angular-dependent magnetoresistance for variation of magnetic fielddirection perpendicular to the charge current direction. Detailed temperature-, magnetic field-,and crystallographic orientation-dependent measurements indicate that interface-generated spincurrent (IGSC) at the RuO2/Py interface predominantly governs the observed magnetoresistance.In addition, the role of IGSC contribution to the observed magnetoresistance was demonstratedthrough drift-diffusion calculations. This shows that strong interface effects dominate over possiblealtermagnetic contributions from RuO2. Our results show that the role of interface-generated spincurrents is crucial and should not be overlooked in studies of altermagnetic systems. A criticalstep in this direction is disentangling interfacial from altermagnetic contributions. The insight intointerfacial contributions from altermagnetic influences is essential for the advancement of RuO2-based spintronic memory and sensing applications.